README.md
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24
25- [Design goals](#design-goals)
26- [Sponsors](#sponsors)
27- [Support](#support) ([documentation](https://json.nlohmann.me), [FAQ](https://json.nlohmann.me/home/faq/), [discussions](https://github.com/nlohmann/json/discussions), [API](https://json.nlohmann.me/api/basic_json/), [bug issues](https://github.com/nlohmann/json/issues))
28- [Examples](#examples)
29 - [Read JSON from a file](#read-json-from-a-file)
30 - [Creating `json` objects from JSON literals](#creating-json-objects-from-json-literals)
31 - [JSON as first-class data type](#json-as-first-class-data-type)
32 - [Serialization / Deserialization](#serialization--deserialization)
33 - [STL-like access](#stl-like-access)
34 - [Conversion from STL containers](#conversion-from-stl-containers)
35 - [JSON Pointer and JSON Patch](#json-pointer-and-json-patch)
36 - [JSON Merge Patch](#json-merge-patch)
37 - [Implicit conversions](#implicit-conversions)
38 - [Conversions to/from arbitrary types](#arbitrary-types-conversions)
39 - [Specializing enum conversion](#specializing-enum-conversion)
40 - [Binary formats (BSON, CBOR, MessagePack, UBJSON, and BJData)](#binary-formats-bson-cbor-messagepack-ubjson-and-bjdata)
41- [Supported compilers](#supported-compilers)
42- [Integration](#integration)
43 - [CMake](#cmake)
44 - [Package Managers](#package-managers)
45 - [Pkg-config](#pkg-config)
46- [License](#license)
47- [Contact](#contact)
48- [Thanks](#thanks)
49- [Used third-party tools](#used-third-party-tools)
50- [Projects using JSON for Modern C++](#projects-using-json-for-modern-c)
51- [Notes](#notes)
52- [Execute unit tests](#execute-unit-tests)
53
54## Design goals
55
56There are myriads of [JSON](https://json.org) libraries out there, and each may even have its reason to exist. Our class had these design goals:
57
58- **Intuitive syntax**. In languages such as Python, JSON feels like a first class data type. We used all the operator magic of modern C++ to achieve the same feeling in your code. Check out the [examples below](#examples) and you'll know what I mean.
59
60- **Trivial integration**. Our whole code consists of a single header file [`json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp). That's it. No library, no subproject, no dependencies, no complex build system. The class is written in vanilla C++11. All in all, everything should require no adjustment of your compiler flags or project settings.
61
62- **Serious testing**. Our code is heavily [unit-tested](https://github.com/nlohmann/json/tree/develop/tests/src) and covers [100%](https://coveralls.io/r/nlohmann/json) of the code, including all exceptional behavior. Furthermore, we checked with [Valgrind](https://valgrind.org) and the [Clang Sanitizers](https://clang.llvm.org/docs/index.html) that there are no memory leaks. [Google OSS-Fuzz](https://github.com/google/oss-fuzz/tree/master/projects/json) additionally runs fuzz tests against all parsers 24/7, effectively executing billions of tests so far. To maintain high quality, the project is following the [Core Infrastructure Initiative (CII) best practices](https://bestpractices.coreinfrastructure.org/projects/289).
63
64Other aspects were not so important to us:
65
66- **Memory efficiency**. Each JSON object has an overhead of one pointer (the maximal size of a union) and one enumeration element (1 byte). The default generalization uses the following C++ data types: `std::string` for strings, `int64_t`, `uint64_t` or `double` for numbers, `std::map` for objects, `std::vector` for arrays, and `bool` for Booleans. However, you can template the generalized class `basic_json` to your needs.
67
68- **Speed**. There are certainly [faster JSON libraries](https://github.com/miloyip/nativejson-benchmark#parsing-time) out there. However, if your goal is to speed up your development by adding JSON support with a single header, then this library is the way to go. If you know how to use a `std::vector` or `std::map`, you are already set.
69
70See the [contribution guidelines](https://github.com/nlohmann/json/blob/master/.github/CONTRIBUTING.md#please-dont) for more information.
71
72
73## Sponsors
74
75You can sponsor this library at [GitHub Sponsors](https://github.com/sponsors/nlohmann).
76
77### :office: Corporate Sponsor
78
79[](https://github.com/codacy)
80
81### :label: Named Sponsors
82
83- [Michael Hartmann](https://github.com/reFX-Mike)
84- [Stefan Hagen](https://github.com/sthagen)
85- [Steve Sperandeo](https://github.com/homer6)
86- [Robert Jefe Lindstädt](https://github.com/eljefedelrodeodeljefe)
87- [Steve Wagner](https://github.com/ciroque)
88
89Thanks everyone!
90
91## Support
92
93:question: If you have a **question**, please check if it is already answered in the [**FAQ**](https://json.nlohmann.me/home/faq/) or the [**Q&A**](https://github.com/nlohmann/json/discussions/categories/q-a) section. If not, please [**ask a new question**](https://github.com/nlohmann/json/discussions/new) there.
94
95:books: If you want to **learn more** about how to use the library, check out the rest of the [**README**](#examples), have a look at [**code examples**](https://github.com/nlohmann/json/tree/develop/docs/examples), or browse through the [**help pages**](https://json.nlohmann.me).
96
97:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/).
98
99:bug: If you found a **bug**, please check the [**FAQ**](https://json.nlohmann.me/home/faq/) if it is a known issue or the result of a design decision. Please also have a look at the [**issue list**](https://github.com/nlohmann/json/issues) before you [**create a new issue**](https://github.com/nlohmann/json/issues/new/choose). Please provide as much information as possible to help us understand and reproduce your issue.
100
101There is also a [**docset**](https://github.com/Kapeli/Dash-User-Contributions/tree/master/docsets/JSON_for_Modern_C%2B%2B) for the documentation browsers [Dash](https://kapeli.com/dash), [Velocity](https://velocity.silverlakesoftware.com), and [Zeal](https://zealdocs.org) that contains the full [documentation](https://json.nlohmann.me) as offline resource.
102
103## Examples
104
105Here are some examples to give you an idea how to use the class.
106
107Beside the examples below, you may want to:
108
109→ Check the [documentation](https://json.nlohmann.me/)\
110→ Browse the [standalone example files](https://github.com/nlohmann/json/tree/develop/docs/examples)
111
112Every API function (documented in the [API Documentation](https://json.nlohmann.me/api/basic_json/)) has a corresponding standalone example file. For example, the [`emplace()`](https://json.nlohmann.me/api/basic_json/emplace/) function has a matching [emplace.cpp](https://github.com/nlohmann/json/blob/develop/docs/examples/emplace.cpp) example file.
113
114### Read JSON from a file
115
116The `json` class provides an API for manipulating a JSON value. To create a `json` object by reading a JSON file:
117
118```cpp
119#include <fstream>
120#include <nlohmann/json.hpp>
121using json = nlohmann::json;
122
123// ...
124
125std::ifstream f("example.json");
126json data = json::parse(f);
127```
128
129### Creating `json` objects from JSON literals
130
131Assume you want to create hard-code this literal JSON value in a file, as a `json` object:
132
133```json
134{
135 "pi": 3.141,
136 "happy": true
137}
138```
139
140There are various options:
141
142```cpp
143// Using (raw) string literals and json::parse
144json ex1 = json::parse(R"(
145 {
146 "pi": 3.141,
147 "happy": true
148 }
149)");
150
151// Using user-defined (raw) string literals
152using namespace nlohmann::literals;
153json ex2 = R"(
154 {
155 "pi": 3.141,
156 "happy": true
157 }
158)"_json;
159
160// Using initializer lists
161json ex3 = {
162 {"happy", true},
163 {"pi", 3.141},
164};
165```
166
167### JSON as first-class data type
168
169Here are some examples to give you an idea how to use the class.
170
171Assume you want to create the JSON object
172
173```json
174{
175 "pi": 3.141,
176 "happy": true,
177 "name": "Niels",
178 "nothing": null,
179 "answer": {
180 "everything": 42
181 },
182 "list": [1, 0, 2],
183 "object": {
184 "currency": "USD",
185 "value": 42.99
186 }
187}
188```
189
190With this library, you could write:
191
192```cpp
193// create an empty structure (null)
194json j;
195
196// add a number that is stored as double (note the implicit conversion of j to an object)
197j["pi"] = 3.141;
198
199// add a Boolean that is stored as bool
200j["happy"] = true;
201
202// add a string that is stored as std::string
203j["name"] = "Niels";
204
205// add another null object by passing nullptr
206j["nothing"] = nullptr;
207
208// add an object inside the object
209j["answer"]["everything"] = 42;
210
211// add an array that is stored as std::vector (using an initializer list)
212j["list"] = { 1, 0, 2 };
213
214// add another object (using an initializer list of pairs)
215j["object"] = { {"currency", "USD"}, {"value", 42.99} };
216
217// instead, you could also write (which looks very similar to the JSON above)
218json j2 = {
219 {"pi", 3.141},
220 {"happy", true},
221 {"name", "Niels"},
222 {"nothing", nullptr},
223 {"answer", {
224 {"everything", 42}
225 }},
226 {"list", {1, 0, 2}},
227 {"object", {
228 {"currency", "USD"},
229 {"value", 42.99}
230 }}
231};
232```
233
234Note that in all these cases, you never need to "tell" the compiler which JSON value type you want to use. If you want to be explicit or express some edge cases, the functions [`json::array()`](https://json.nlohmann.me/api/basic_json/array/) and [`json::object()`](https://json.nlohmann.me/api/basic_json/object/) will help:
235
236```cpp
237// a way to express the empty array []
238json empty_array_explicit = json::array();
239
240// ways to express the empty object {}
241json empty_object_implicit = json({});
242json empty_object_explicit = json::object();
243
244// a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]]
245json array_not_object = json::array({ {"currency", "USD"}, {"value", 42.99} });
246```
247
248### Serialization / Deserialization
249
250#### To/from strings
251
252You can create a JSON value (deserialization) by appending `_json` to a string literal:
253
254```cpp
255// create object from string literal
256json j = "{ \"happy\": true, \"pi\": 3.141 }"_json;
257
258// or even nicer with a raw string literal
259auto j2 = R"(
260 {
261 "happy": true,
262 "pi": 3.141
263 }
264)"_json;
265```
266
267Note that without appending the `_json` suffix, the passed string literal is not parsed, but just used as JSON string
268value. That is, `json j = "{ \"happy\": true, \"pi\": 3.141 }"` would just store the string
269`"{ "happy": true, "pi": 3.141 }"` rather than parsing the actual object.
270
271The string literal should be brought into scope with with `using namespace nlohmann::literals;`
272(see [`json::parse()`](https://json.nlohmann.me/api/operator_literal_json/)).
273
274The above example can also be expressed explicitly using [`json::parse()`](https://json.nlohmann.me/api/basic_json/parse/):
275
276```cpp
277// parse explicitly
278auto j3 = json::parse(R"({"happy": true, "pi": 3.141})");
279```
280
281You can also get a string representation of a JSON value (serialize):
282
283```cpp
284// explicit conversion to string
285std::string s = j.dump(); // {"happy":true,"pi":3.141}
286
287// serialization with pretty printing
288// pass in the amount of spaces to indent
289std::cout << j.dump(4) << std::endl;
290// {
291// "happy": true,
292// "pi": 3.141
293// }
294```
295
296Note the difference between serialization and assignment:
297
298```cpp
299// store a string in a JSON value
300json j_string = "this is a string";
301
302// retrieve the string value
303auto cpp_string = j_string.get<std::string>();
304// retrieve the string value (alternative when a variable already exists)
305std::string cpp_string2;
306j_string.get_to(cpp_string2);
307
308// retrieve the serialized value (explicit JSON serialization)
309std::string serialized_string = j_string.dump();
310
311// output of original string
312std::cout << cpp_string << " == " << cpp_string2 << " == " << j_string.get<std::string>() << '\n';
313// output of serialized value
314std::cout << j_string << " == " << serialized_string << std::endl;
315```
316
317[`.dump()`](https://json.nlohmann.me/api/basic_json/dump/) returns the originally stored string value.
318
319Note the library only supports UTF-8. When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace` or `json::error_handler_t::ignore` are used as error handlers.
320
321#### To/from streams (e.g. files, string streams)
322
323You can also use streams to serialize and deserialize:
324
325```cpp
326// deserialize from standard input
327json j;
328std::cin >> j;
329
330// serialize to standard output
331std::cout << j;
332
333// the setw manipulator was overloaded to set the indentation for pretty printing
334std::cout << std::setw(4) << j << std::endl;
335```
336
337These operators work for any subclasses of `std::istream` or `std::ostream`. Here is the same example with files:
338
339```cpp
340// read a JSON file
341std::ifstream i("file.json");
342json j;
343i >> j;
344
345// write prettified JSON to another file
346std::ofstream o("pretty.json");
347o << std::setw(4) << j << std::endl;
348```
349
350Please note that setting the exception bit for `failbit` is inappropriate for this use case. It will result in program termination due to the `noexcept` specifier in use.
351
352#### Read from iterator range
353
354You can also parse JSON from an iterator range; that is, from any container accessible by iterators whose `value_type` is an integral type of 1, 2 or 4 bytes, which will be interpreted as UTF-8, UTF-16 and UTF-32 respectively. For instance, a `std::vector<std::uint8_t>`, or a `std::list<std::uint16_t>`:
355
356```cpp
357std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'};
358json j = json::parse(v.begin(), v.end());
359```
360
361You may leave the iterators for the range [begin, end):
362
363```cpp
364std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'};
365json j = json::parse(v);
366```
367
368#### Custom data source
369
370Since the parse function accepts arbitrary iterator ranges, you can provide your own data sources by implementing the `LegacyInputIterator` concept.
371
372```cpp
373struct MyContainer {
374 void advance();
375 const char& get_current();
376};
377
378struct MyIterator {
379 using difference_type = std::ptrdiff_t;
380 using value_type = char;
381 using pointer = const char*;
382 using reference = const char&;
383 using iterator_category = std::input_iterator_tag;
384
385 MyIterator& operator++() {
386 MyContainer.advance();
387 return *this;
388 }
389
390 bool operator!=(const MyIterator& rhs) const {
391 return rhs.target != target;
392 }
393
394 reference operator*() const {
395 return target.get_current();
396 }
397
398 MyContainer* target = nullptr;
399};
400
401MyIterator begin(MyContainer& tgt) {
402 return MyIterator{&tgt};
403}
404
405MyIterator end(const MyContainer&) {
406 return {};
407}
408
409void foo() {
410 MyContainer c;
411 json j = json::parse(c);
412}
413```
414
415#### SAX interface
416
417The library uses a SAX-like interface with the following functions:
418
419```cpp
420// called when null is parsed
421bool null();
422
423// called when a boolean is parsed; value is passed
424bool boolean(bool val);
425
426// called when a signed or unsigned integer number is parsed; value is passed
427bool number_integer(number_integer_t val);
428bool number_unsigned(number_unsigned_t val);
429
430// called when a floating-point number is parsed; value and original string is passed
431bool number_float(number_float_t val, const string_t& s);
432
433// called when a string is parsed; value is passed and can be safely moved away
434bool string(string_t& val);
435// called when a binary value is parsed; value is passed and can be safely moved away
436bool binary(binary_t& val);
437
438// called when an object or array begins or ends, resp. The number of elements is passed (or -1 if not known)
439bool start_object(std::size_t elements);
440bool end_object();
441bool start_array(std::size_t elements);
442bool end_array();
443// called when an object key is parsed; value is passed and can be safely moved away
444bool key(string_t& val);
445
446// called when a parse error occurs; byte position, the last token, and an exception is passed
447bool parse_error(std::size_t position, const std::string& last_token, const detail::exception& ex);
448```
449
450The return value of each function determines whether parsing should proceed.
451
452To implement your own SAX handler, proceed as follows:
453
4541. Implement the SAX interface in a class. You can use class `nlohmann::json_sax<json>` as base class, but you can also use any class where the functions described above are implemented and public.
4552. Create an object of your SAX interface class, e.g. `my_sax`.
4563. Call `bool json::sax_parse(input, &my_sax)`; where the first parameter can be any input like a string or an input stream and the second parameter is a pointer to your SAX interface.
457
458Note the `sax_parse` function only returns a `bool` indicating the result of the last executed SAX event. It does not return a `json` value - it is up to you to decide what to do with the SAX events. Furthermore, no exceptions are thrown in case of a parse error - it is up to you what to do with the exception object passed to your `parse_error` implementation. Internally, the SAX interface is used for the DOM parser (class `json_sax_dom_parser`) as well as the acceptor (`json_sax_acceptor`), see file [`json_sax.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/input/json_sax.hpp).
459
460### STL-like access
461
462We designed the JSON class to behave just like an STL container. In fact, it satisfies the [**ReversibleContainer**](https://en.cppreference.com/w/cpp/named_req/ReversibleContainer) requirement.
463
464```cpp
465// create an array using push_back
466json j;
467j.push_back("foo");
468j.push_back(1);
469j.push_back(true);
470
471// also use emplace_back
472j.emplace_back(1.78);
473
474// iterate the array
475for (json::iterator it = j.begin(); it != j.end(); ++it) {
476 std::cout << *it << '\n';
477}
478
479// range-based for
480for (auto& element : j) {
481 std::cout << element << '\n';
482}
483
484// getter/setter
485const auto tmp = j[0].get<std::string>();
486j[1] = 42;
487bool foo = j.at(2);
488
489// comparison
490j == R"(["foo", 1, true, 1.78])"_json; // true
491
492// other stuff
493j.size(); // 4 entries
494j.empty(); // false
495j.type(); // json::value_t::array
496j.clear(); // the array is empty again
497
498// convenience type checkers
499j.is_null();
500j.is_boolean();
501j.is_number();
502j.is_object();
503j.is_array();
504j.is_string();
505
506// create an object
507json o;
508o["foo"] = 23;
509o["bar"] = false;
510o["baz"] = 3.141;
511
512// also use emplace
513o.emplace("weather", "sunny");
514
515// special iterator member functions for objects
516for (json::iterator it = o.begin(); it != o.end(); ++it) {
517 std::cout << it.key() << " : " << it.value() << "\n";
518}
519
520// the same code as range for
521for (auto& el : o.items()) {
522 std::cout << el.key() << " : " << el.value() << "\n";
523}
524
525// even easier with structured bindings (C++17)
526for (auto& [key, value] : o.items()) {
527 std::cout << key << " : " << value << "\n";
528}
529
530// find an entry
531if (o.contains("foo")) {
532 // there is an entry with key "foo"
533}
534
535// or via find and an iterator
536if (o.find("foo") != o.end()) {
537 // there is an entry with key "foo"
538}
539
540// or simpler using count()
541int foo_present = o.count("foo"); // 1
542int fob_present = o.count("fob"); // 0
543
544// delete an entry
545o.erase("foo");
546```
547
548
549### Conversion from STL containers
550
551Any sequence container (`std::array`, `std::vector`, `std::deque`, `std::forward_list`, `std::list`) whose values can be used to construct JSON values (e.g., integers, floating point numbers, Booleans, string types, or again STL containers described in this section) can be used to create a JSON array. The same holds for similar associative containers (`std::set`, `std::multiset`, `std::unordered_set`, `std::unordered_multiset`), but in these cases the order of the elements of the array depends on how the elements are ordered in the respective STL container.
552
553```cpp
554std::vector<int> c_vector {1, 2, 3, 4};
555json j_vec(c_vector);
556// [1, 2, 3, 4]
557
558std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6};
559json j_deque(c_deque);
560// [1.2, 2.3, 3.4, 5.6]
561
562std::list<bool> c_list {true, true, false, true};
563json j_list(c_list);
564// [true, true, false, true]
565
566std::forward_list<int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543};
567json j_flist(c_flist);
568// [12345678909876, 23456789098765, 34567890987654, 45678909876543]
569
570std::array<unsigned long, 4> c_array {{1, 2, 3, 4}};
571json j_array(c_array);
572// [1, 2, 3, 4]
573
574std::set<std::string> c_set {"one", "two", "three", "four", "one"};
575json j_set(c_set); // only one entry for "one" is used
576// ["four", "one", "three", "two"]
577
578std::unordered_set<std::string> c_uset {"one", "two", "three", "four", "one"};
579json j_uset(c_uset); // only one entry for "one" is used
580// maybe ["two", "three", "four", "one"]
581
582std::multiset<std::string> c_mset {"one", "two", "one", "four"};
583json j_mset(c_mset); // both entries for "one" are used
584// maybe ["one", "two", "one", "four"]
585
586std::unordered_multiset<std::string> c_umset {"one", "two", "one", "four"};
587json j_umset(c_umset); // both entries for "one" are used
588// maybe ["one", "two", "one", "four"]
589```
590
591Likewise, any associative key-value containers (`std::map`, `std::multimap`, `std::unordered_map`, `std::unordered_multimap`) whose keys can construct an `std::string` and whose values can be used to construct JSON values (see examples above) can be used to create a JSON object. Note that in case of multimaps only one key is used in the JSON object and the value depends on the internal order of the STL container.
592
593```cpp
594std::map<std::string, int> c_map { {"one", 1}, {"two", 2}, {"three", 3} };
595json j_map(c_map);
596// {"one": 1, "three": 3, "two": 2 }
597
598std::unordered_map<const char*, double> c_umap { {"one", 1.2}, {"two", 2.3}, {"three", 3.4} };
599json j_umap(c_umap);
600// {"one": 1.2, "two": 2.3, "three": 3.4}
601
602std::multimap<std::string, bool> c_mmap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
603json j_mmap(c_mmap); // only one entry for key "three" is used
604// maybe {"one": true, "two": true, "three": true}
605
606std::unordered_multimap<std::string, bool> c_ummap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
607json j_ummap(c_ummap); // only one entry for key "three" is used
608// maybe {"one": true, "two": true, "three": true}
609```
610
611### JSON Pointer and JSON Patch
612
613The library supports **JSON Pointer** ([RFC 6901](https://tools.ietf.org/html/rfc6901)) as alternative means to address structured values. On top of this, **JSON Patch** ([RFC 6902](https://tools.ietf.org/html/rfc6902)) allows describing differences between two JSON values - effectively allowing patch and diff operations known from Unix.
614
615```cpp
616// a JSON value
617json j_original = R"({
618 "baz": ["one", "two", "three"],
619 "foo": "bar"
620})"_json;
621
622// access members with a JSON pointer (RFC 6901)
623j_original["/baz/1"_json_pointer];
624// "two"
625
626// a JSON patch (RFC 6902)
627json j_patch = R"([
628 { "op": "replace", "path": "/baz", "value": "boo" },
629 { "op": "add", "path": "/hello", "value": ["world"] },
630 { "op": "remove", "path": "/foo"}
631])"_json;
632
633// apply the patch
634json j_result = j_original.patch(j_patch);
635// {
636// "baz": "boo",
637// "hello": ["world"]
638// }
639
640// calculate a JSON patch from two JSON values
641json::diff(j_result, j_original);
642// [
643// { "op":" replace", "path": "/baz", "value": ["one", "two", "three"] },
644// { "op": "remove","path": "/hello" },
645// { "op": "add", "path": "/foo", "value": "bar" }
646// ]
647```
648
649### JSON Merge Patch
650
651The library supports **JSON Merge Patch** ([RFC 7386](https://tools.ietf.org/html/rfc7386)) as a patch format. Instead of using JSON Pointer (see above) to specify values to be manipulated, it describes the changes using a syntax that closely mimics the document being modified.
652
653```cpp
654// a JSON value
655json j_document = R"({
656 "a": "b",
657 "c": {
658 "d": "e",
659 "f": "g"
660 }
661})"_json;
662
663// a patch
664json j_patch = R"({
665 "a":"z",
666 "c": {
667 "f": null
668 }
669})"_json;
670
671// apply the patch
672j_document.merge_patch(j_patch);
673// {
674// "a": "z",
675// "c": {
676// "d": "e"
677// }
678// }
679```
680
681### Implicit conversions
682
683Supported types can be implicitly converted to JSON values.
684
685It is recommended to **NOT USE** implicit conversions **FROM** a JSON value.
686You can find more details about this recommendation [here](https://www.github.com/nlohmann/json/issues/958).
687You can switch off implicit conversions by defining `JSON_USE_IMPLICIT_CONVERSIONS` to `0` before including the `json.hpp` header. When using CMake, you can also achieve this by setting the option `JSON_ImplicitConversions` to `OFF`.
688
689```cpp
690// strings
691std::string s1 = "Hello, world!";
692json js = s1;
693auto s2 = js.get<std::string>();
694// NOT RECOMMENDED
695std::string s3 = js;
696std::string s4;
697s4 = js;
698
699// Booleans
700bool b1 = true;
701json jb = b1;
702auto b2 = jb.get<bool>();
703// NOT RECOMMENDED
704bool b3 = jb;
705bool b4;
706b4 = jb;
707
708// numbers
709int i = 42;
710json jn = i;
711auto f = jn.get<double>();
712// NOT RECOMMENDED
713double f2 = jb;
714double f3;
715f3 = jb;
716
717// etc.
718```
719
720Note that `char` types are not automatically converted to JSON strings, but to integer numbers. A conversion to a string must be specified explicitly:
721
722```cpp
723char ch = 'A'; // ASCII value 65
724json j_default = ch; // stores integer number 65
725json j_string = std::string(1, ch); // stores string "A"
726```
727
728### Arbitrary types conversions
729
730Every type can be serialized in JSON, not just STL containers and scalar types. Usually, you would do something along those lines:
731
732```cpp
733namespace ns {
734 // a simple struct to model a person
735 struct person {
736 std::string name;
737 std::string address;
738 int age;
739 };
740}
741
742ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
743
744// convert to JSON: copy each value into the JSON object
745json j;
746j["name"] = p.name;
747j["address"] = p.address;
748j["age"] = p.age;
749
750// ...
751
752// convert from JSON: copy each value from the JSON object
753ns::person p {
754 j["name"].get<std::string>(),
755 j["address"].get<std::string>(),
756 j["age"].get<int>()
757};
758```
759
760It works, but that's quite a lot of boilerplate... Fortunately, there's a better way:
761
762```cpp
763// create a person
764ns::person p {"Ned Flanders", "744 Evergreen Terrace", 60};
765
766// conversion: person -> json
767json j = p;
768
769std::cout << j << std::endl;
770// {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
771
772// conversion: json -> person
773auto p2 = j.get<ns::person>();
774
775// that's it
776assert(p == p2);
777```
778
779#### Basic usage
780
781To make this work with one of your types, you only need to provide two functions:
782
783```cpp
784using json = nlohmann::json;
785
786namespace ns {
787 void to_json(json& j, const person& p) {
788 j = json{{"name", p.name}, {"address", p.address}, {"age", p.age}};
789 }
790
791 void from_json(const json& j, person& p) {
792 j.at("name").get_to(p.name);
793 j.at("address").get_to(p.address);
794 j.at("age").get_to(p.age);
795 }
796} // namespace ns
797```
798
799That's all! When calling the `json` constructor with your type, your custom `to_json` method will be automatically called.
800Likewise, when calling `get<your_type>()` or `get_to(your_type&)`, the `from_json` method will be called.
801
802Some important things:
803
804* Those methods **MUST** be in your type's namespace (which can be the global namespace), or the library will not be able to locate them (in this example, they are in namespace `ns`, where `person` is defined).
805* Those methods **MUST** be available (e.g., proper headers must be included) everywhere you use these conversions. Look at [issue 1108](https://github.com/nlohmann/json/issues/1108) for errors that may occur otherwise.
806* When using `get<your_type>()`, `your_type` **MUST** be [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible). (There is a way to bypass this requirement described later.)
807* In function `from_json`, use function [`at()`](https://json.nlohmann.me/api/basic_json/at/) to access the object values rather than `operator[]`. In case a key does not exist, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior.
808* You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these.
809
810#### Simplify your life with macros
811
812If you just want to serialize/deserialize some structs, the `to_json`/`from_json` functions can be a lot of boilerplate.
813
814There are two macros to make your life easier as long as you (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object:
815
816- `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)` is to be defined inside the namespace of the class/struct to create code for.
817- `NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)` is to be defined inside the class/struct to create code for. This macro can also access private members.
818
819In both macros, the first parameter is the name of the class/struct, and all remaining parameters name the members.
820
821##### Examples
822
823The `to_json`/`from_json` functions for the `person` struct above can be created with:
824
825```cpp
826namespace ns {
827 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, address, age)
828}
829```
830
831Here is an example with private members, where `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is needed:
832
833```cpp
834namespace ns {
835 class address {
836 private:
837 std::string street;
838 int housenumber;
839 int postcode;
840
841 public:
842 NLOHMANN_DEFINE_TYPE_INTRUSIVE(address, street, housenumber, postcode)
843 };
844}
845```
846
847#### How do I convert third-party types?
848
849This requires a bit more advanced technique. But first, let's see how this conversion mechanism works:
850
851The library uses **JSON Serializers** to convert types to json.
852The default serializer for `nlohmann::json` is `nlohmann::adl_serializer` (ADL means [Argument-Dependent Lookup](https://en.cppreference.com/w/cpp/language/adl)).
853
854It is implemented like this (simplified):
855
856```cpp
857template <typename T>
858struct adl_serializer {
859 static void to_json(json& j, const T& value) {
860 // calls the "to_json" method in T's namespace
861 }
862
863 static void from_json(const json& j, T& value) {
864 // same thing, but with the "from_json" method
865 }
866};
867```
868
869This serializer works fine when you have control over the type's namespace. However, what about `boost::optional` or `std::filesystem::path` (C++17)? Hijacking the `boost` namespace is pretty bad, and it's illegal to add something other than template specializations to `std`...
870
871To solve this, you need to add a specialization of `adl_serializer` to the `nlohmann` namespace, here's an example:
872
873```cpp
874// partial specialization (full specialization works too)
875namespace nlohmann {
876 template <typename T>
877 struct adl_serializer<boost::optional<T>> {
878 static void to_json(json& j, const boost::optional<T>& opt) {
879 if (opt == boost::none) {
880 j = nullptr;
881 } else {
882 j = *opt; // this will call adl_serializer<T>::to_json which will
883 // find the free function to_json in T's namespace!
884 }
885 }
886
887 static void from_json(const json& j, boost::optional<T>& opt) {
888 if (j.is_null()) {
889 opt = boost::none;
890 } else {
891 opt = j.get<T>(); // same as above, but with
892 // adl_serializer<T>::from_json
893 }
894 }
895 };
896}
897```
898
899#### How can I use `get()` for non-default constructible/non-copyable types?
900
901There is a way, if your type is [MoveConstructible](https://en.cppreference.com/w/cpp/named_req/MoveConstructible). You will need to specialize the `adl_serializer` as well, but with a special `from_json` overload:
902
903```cpp
904struct move_only_type {
905 move_only_type() = delete;
906 move_only_type(int ii): i(ii) {}
907 move_only_type(const move_only_type&) = delete;
908 move_only_type(move_only_type&&) = default;
909
910 int i;
911};
912
913namespace nlohmann {
914 template <>
915 struct adl_serializer<move_only_type> {
916 // note: the return type is no longer 'void', and the method only takes
917 // one argument
918 static move_only_type from_json(const json& j) {
919 return {j.get<int>()};
920 }
921
922 // Here's the catch! You must provide a to_json method! Otherwise, you
923 // will not be able to convert move_only_type to json, since you fully
924 // specialized adl_serializer on that type
925 static void to_json(json& j, move_only_type t) {
926 j = t.i;
927 }
928 };
929}
930```
931
932#### Can I write my own serializer? (Advanced use)
933
934Yes. You might want to take a look at [`unit-udt.cpp`](https://github.com/nlohmann/json/blob/develop/tests/src/unit-udt.cpp) in the test suite, to see a few examples.
935
936If you write your own serializer, you'll need to do a few things:
937
938- use a different `basic_json` alias than `nlohmann::json` (the last template parameter of `basic_json` is the `JSONSerializer`)
939- use your `basic_json` alias (or a template parameter) in all your `to_json`/`from_json` methods
940- use `nlohmann::to_json` and `nlohmann::from_json` when you need ADL
941
942Here is an example, without simplifications, that only accepts types with a size <= 32, and uses ADL.
943
944```cpp
945// You should use void as a second template argument
946// if you don't need compile-time checks on T
947template<typename T, typename SFINAE = typename std::enable_if<sizeof(T) <= 32>::type>
948struct less_than_32_serializer {
949 template <typename BasicJsonType>
950 static void to_json(BasicJsonType& j, T value) {
951 // we want to use ADL, and call the correct to_json overload
952 using nlohmann::to_json; // this method is called by adl_serializer,
953 // this is where the magic happens
954 to_json(j, value);
955 }
956
957 template <typename BasicJsonType>
958 static void from_json(const BasicJsonType& j, T& value) {
959 // same thing here
960 using nlohmann::from_json;
961 from_json(j, value);
962 }
963};
964```
965
966Be **very** careful when reimplementing your serializer, you can stack overflow if you don't pay attention:
967
968```cpp
969template <typename T, void>
970struct bad_serializer
971{
972 template <typename BasicJsonType>
973 static void to_json(BasicJsonType& j, const T& value) {
974 // this calls BasicJsonType::json_serializer<T>::to_json(j, value);
975 // if BasicJsonType::json_serializer == bad_serializer ... oops!
976 j = value;
977 }
978
979 template <typename BasicJsonType>
980 static void to_json(const BasicJsonType& j, T& value) {
981 // this calls BasicJsonType::json_serializer<T>::from_json(j, value);
982 // if BasicJsonType::json_serializer == bad_serializer ... oops!
983 value = j.template get<T>(); // oops!
984 }
985};
986```
987
988### Specializing enum conversion
989
990By default, enum values are serialized to JSON as integers. In some cases this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to JSON, the later de-serialized JSON data may be undefined or a different enum value than was originally intended.
991
992It is possible to more precisely specify how a given enum is mapped to and from JSON as shown below:
993
994```cpp
995// example enum type declaration
996enum TaskState {
997 TS_STOPPED,
998 TS_RUNNING,
999 TS_COMPLETED,
1000 TS_INVALID=-1,
1001};
1002
1003// map TaskState values to JSON as strings
1004NLOHMANN_JSON_SERIALIZE_ENUM( TaskState, {
1005 {TS_INVALID, nullptr},
1006 {TS_STOPPED, "stopped"},
1007 {TS_RUNNING, "running"},
1008 {TS_COMPLETED, "completed"},
1009})
1010```
1011
1012The `NLOHMANN_JSON_SERIALIZE_ENUM()` macro declares a set of `to_json()` / `from_json()` functions for type `TaskState` while avoiding repetition and boilerplate serialization code.
1013
1014**Usage:**
1015
1016```cpp
1017// enum to JSON as string
1018json j = TS_STOPPED;
1019assert(j == "stopped");
1020
1021// json string to enum
1022json j3 = "running";
1023assert(j3.get<TaskState>() == TS_RUNNING);
1024
1025// undefined json value to enum (where the first map entry above is the default)
1026json jPi = 3.14;
1027assert(jPi.get<TaskState>() == TS_INVALID );
1028```
1029
1030Just as in [Arbitrary Type Conversions](#arbitrary-types-conversions) above,
1031- `NLOHMANN_JSON_SERIALIZE_ENUM()` MUST be declared in your enum type's namespace (which can be the global namespace), or the library will not be able to locate it, and it will default to integer serialization.
1032- It MUST be available (e.g., proper headers must be included) everywhere you use the conversions.
1033
1034Other Important points:
1035- When using `get<ENUM_TYPE>()`, undefined JSON values will default to the first pair specified in your map. Select this default pair carefully.
1036- If an enum or JSON value is specified more than once in your map, the first matching occurrence from the top of the map will be returned when converting to or from JSON.
1037
1038### Binary formats (BSON, CBOR, MessagePack, UBJSON, and BJData)
1039
1040Though JSON is a ubiquitous data format, it is not a very compact format suitable for data exchange, for instance over a network. Hence, the library supports [BSON](https://bsonspec.org) (Binary JSON), [CBOR](https://cbor.io) (Concise Binary Object Representation), [MessagePack](https://msgpack.org), [UBJSON](https://ubjson.org) (Universal Binary JSON Specification) and [BJData](https://neurojson.org/bjdata) (Binary JData) to efficiently encode JSON values to byte vectors and to decode such vectors.
1041
1042```cpp
1043// create a JSON value
1044json j = R"({"compact": true, "schema": 0})"_json;
1045
1046// serialize to BSON
1047std::vector<std::uint8_t> v_bson = json::to_bson(j);
1048
1049// 0x1B, 0x00, 0x00, 0x00, 0x08, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x00, 0x01, 0x10, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
1050
1051// roundtrip
1052json j_from_bson = json::from_bson(v_bson);
1053
1054// serialize to CBOR
1055std::vector<std::uint8_t> v_cbor = json::to_cbor(j);
1056
1057// 0xA2, 0x67, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xF5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00
1058
1059// roundtrip
1060json j_from_cbor = json::from_cbor(v_cbor);
1061
1062// serialize to MessagePack
1063std::vector<std::uint8_t> v_msgpack = json::to_msgpack(j);
1064
1065// 0x82, 0xA7, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xC3, 0xA6, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00
1066
1067// roundtrip
1068json j_from_msgpack = json::from_msgpack(v_msgpack);
1069
1070// serialize to UBJSON
1071std::vector<std::uint8_t> v_ubjson = json::to_ubjson(j);
1072
1073// 0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D
1074
1075// roundtrip
1076json j_from_ubjson = json::from_ubjson(v_ubjson);
1077```
1078
1079The library also supports binary types from BSON, CBOR (byte strings), and MessagePack (bin, ext, fixext). They are stored by default as `std::vector<std::uint8_t>` to be processed outside the library.
1080
1081```cpp
1082// CBOR byte string with payload 0xCAFE
1083std::vector<std::uint8_t> v = {0x42, 0xCA, 0xFE};
1084
1085// read value
1086json j = json::from_cbor(v);
1087
1088// the JSON value has type binary
1089j.is_binary(); // true
1090
1091// get reference to stored binary value
1092auto& binary = j.get_binary();
1093
1094// the binary value has no subtype (CBOR has no binary subtypes)
1095binary.has_subtype(); // false
1096
1097// access std::vector<std::uint8_t> member functions
1098binary.size(); // 2
1099binary[0]; // 0xCA
1100binary[1]; // 0xFE
1101
1102// set subtype to 0x10
1103binary.set_subtype(0x10);
1104
1105// serialize to MessagePack
1106auto cbor = json::to_msgpack(j); // 0xD5 (fixext2), 0x10, 0xCA, 0xFE
1107```
1108
1109
1110## Supported compilers
1111
1112Though it's 2022 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:
1113
1114- GCC 4.8 - 12.0 (and possibly later)
1115- Clang 3.4 - 15.0 (and possibly later)
1116- Apple Clang 9.1 - 13.1 (and possibly later)
1117- Intel C++ Compiler 17.0.2 (and possibly later)
1118- Nvidia CUDA Compiler 11.0.221 (and possibly later)
1119- Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later)
1120- Microsoft Visual C++ 2017 / Build Tools 15.5.180.51428 (and possibly later)
1121- Microsoft Visual C++ 2019 / Build Tools 16.3.1+1def00d3d (and possibly later)
1122- Microsoft Visual C++ 2022 / Build Tools 19.30.30709.0 (and possibly later)
1123
1124I would be happy to learn about other compilers/versions.
1125
1126Please note:
1127
1128- GCC 4.8 has a bug [57824](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57824)): multiline raw strings cannot be the arguments to macros. Don't use multiline raw strings directly in macros with this compiler.
1129- Android defaults to using very old compilers and C++ libraries. To fix this, add the following to your `Application.mk`. This will switch to the LLVM C++ library, the Clang compiler, and enable C++11 and other features disabled by default.
1130
1131 ```
1132 APP_STL := c++_shared
1133 NDK_TOOLCHAIN_VERSION := clang3.6
1134 APP_CPPFLAGS += -frtti -fexceptions
1135 ```
1136
1137 The code compiles successfully with [Android NDK](https://developer.android.com/ndk/index.html?hl=ml), Revision 9 - 11 (and possibly later) and [CrystaX's Android NDK](https://www.crystax.net/en/android/ndk) version 10.
1138
1139- For GCC running on MinGW or Android SDK, the error `'to_string' is not a member of 'std'` (or similarly, for `strtod` or `strtof`) may occur. Note this is not an issue with the code, but rather with the compiler itself. On Android, see above to build with a newer environment. For MinGW, please refer to [this site](https://tehsausage.com/mingw-to-string) and [this discussion](https://github.com/nlohmann/json/issues/136) for information on how to fix this bug. For Android NDK using `APP_STL := gnustl_static`, please refer to [this discussion](https://github.com/nlohmann/json/issues/219).
1140
1141- Unsupported versions of GCC and Clang are rejected by `#error` directives. This can be switched off by defining `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`. Note that you can expect no support in this case.
1142
1143The following compilers are currently used in continuous integration at [AppVeyor](https://ci.appveyor.com/project/nlohmann/json), [Drone CI](https://cloud.drone.io/nlohmann/json), and [GitHub Actions](https://github.com/nlohmann/json/actions):
1144
1145| Compiler | Operating System | CI Provider |
1146|--------------------------------------------------------------------------------------------------------|--------------------|----------------|
1147| Apple Clang 11.0.3 (clang-1103.0.32.62); Xcode 11.7 | macOS 11.6.8 | GitHub Actions |
1148| Apple Clang 12.0.0 (clang-1200.0.32.29); Xcode 12.4 | macOS 11.6.8 | GitHub Actions |
1149| Apple Clang 12.0.5 (clang-1205.0.22.11); Xcode 12.5.1 | macOS 11.6.8 | GitHub Actions |
1150| Apple Clang 13.0.0 (clang-1300.0.29.3); Xcode 13.0 | macOS 11.6.8 | GitHub Actions |
1151| Apple Clang 13.0.0 (clang-1300.0.29.3); Xcode 13.1 | macOS 12.4 | GitHub Actions |
1152| Apple Clang 13.0.0 (clang-1300.0.29.30); Xcode 13.2.1 | macOS 12.4 | GitHub Actions |
1153| Apple Clang 13.1.6 (clang-1316.0.21.2.3); Xcode 13.3.1 | macOS 12.4 | GitHub Actions |
1154| Apple Clang 13.1.6 (clang-1316.0.21.2.5); Xcode 13.4.1 | macOS 12.4 | GitHub Actions |
1155| Clang 3.5.2 (3.5.2-3ubuntu1) | Ubuntu 20.04.3 LTS | GitHub Actions |
1156| Clang 3.6.2 (3.6.2-3ubuntu2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1157| Clang 3.7.1 (3.7.1-2ubuntu2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1158| Clang 3.8.0 (3.8.0-2ubuntu4) | Ubuntu 20.04.3 LTS | GitHub Actions |
1159| Clang 3.9.1 (3.9.1-4ubuntu3\~16.04.2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1160| Clang 4.0.0 (4.0.0-1ubuntu1\~16.04.2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1161| Clang 5.0.0 (5.0.0-3\~16.04.1) | Ubuntu 20.04.3 LTS | GitHub Actions |
1162| Clang 6.0.1 (6.0.1-14) | Ubuntu 20.04.3 LTS | GitHub Actions |
1163| Clang 7.0.1 (7.0.1-12) | Ubuntu 20.04.3 LTS | GitHub Actions |
1164| Clang 8.0.1 (8.0.1-9) | Ubuntu 20.04.3 LTS | GitHub Actions |
1165| Clang 9.0.1 (9.0.1-12) | Ubuntu 20.04.3 LTS | GitHub Actions |
1166| Clang 10.0.0 (10.0.0-4ubuntu1) | Ubuntu 20.04.3 LTS | GitHub Actions |
1167| Clang 10.0.0 with GNU-like command-line | Windows-10.0.17763 | GitHub Actions |
1168| Clang 11.0.0 with GNU-like command-line | Windows-10.0.17763 | GitHub Actions |
1169| Clang 11.0.0 with MSVC-like command-line | Windows-10.0.17763 | GitHub Actions |
1170| Clang 11.0.0 (11.0.0-2~ubuntu20.04.1) | Ubuntu 20.04.3 LTS | GitHub Actions |
1171| Clang 12.0.0 (12.0.0-3ubuntu1~20.04.3) | Ubuntu 20.04.3 LTS | GitHub Actions |
1172| Clang 13.0.1 (13.0.1-++20211015123032+cf15ccdeb6d5-1exp120211015003613.5) | Ubuntu 20.04.3 LTS | GitHub Actions |
1173| Clang 14.0.5-++20220603124341+2f0a69c32a4c-1~exp1~20220603124352.149 | Ubuntu 20.04.3 LTS | GitHub Actions |
1174| Clang 15.0.0 (15.0.0-++20220530052901+b7d2b160c3ba-1~exp1~20220530172952.268) | Ubuntu 20.04.3 LTS | GitHub Actions |
1175| GCC 4.8.5 (Ubuntu 4.8.5-4ubuntu2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1176| GCC 4.9.3 (Ubuntu 4.9.3-13ubuntu2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1177| GCC 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.12) | Ubuntu 20.04.3 LTS | GitHub Actions |
1178| GCC 6.4.0 (Ubuntu 6.4.0-17ubuntu1) | Ubuntu 20.04.3 LTS | GitHub Actions |
1179| GCC 7.5.0 (Ubuntu 7.5.0-6ubuntu2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1180| GCC 8.1.0 (i686-posix-dwarf-rev0, Built by MinGW-W64 project) | Windows-10.0.17763 | GitHub Actions |
1181| GCC 8.1.0 (x86_64-posix-seh-rev0, Built by MinGW-W64 project) | Windows-10.0.17763 | GitHub Actions |
1182| GCC 8.4.0 (Ubuntu 8.4.0-3ubuntu2) | Ubuntu 20.04.3 LTS | GitHub Actions |
1183| GCC 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) | Ubuntu 20.04.3 LTS | GitHub Actions |
1184| GCC 10.2.0 (Ubuntu 10.2.0-5ubuntu1~20.04) | Ubuntu 20.04.3 LTS | GitHub Actions |
1185| GCC 11.1.0 | Ubuntu (aarch64) | Drone CI |
1186| GCC 11.1.0 (Ubuntu 11.1.0-1ubuntu1~20.04) | Ubuntu 20.04.3 LTS | GitHub Actions |
1187| GCC 13.0.0 13.0.0 20220605 (experimental) | Ubuntu 20.04.3 LTS | GitHub Actions |
1188| Intel C++ Compiler 2021.5.0.20211109 | Ubuntu 20.04.3 LTS | GitHub Actions |
1189| NVCC 11.0.221 | Ubuntu 20.04.3 LTS | GitHub Actions |
1190| Visual Studio 14 2015 MSVC 19.0.24241.7 (Build Engine version 14.0.25420.1) | Windows-6.3.9600 | AppVeyor |
1191| Visual Studio 15 2017 MSVC 19.16.27035.0 (Build Engine version 15.9.21+g9802d43bc3 for .NET Framework) | Windows-10.0.14393 | AppVeyor |
1192| Visual Studio 16 2019 MSVC 19.28.29912.0 (Build Engine version 16.9.0+57a23d249 for .NET Framework) | Windows-10.0.17763 | GitHub Actions |
1193| Visual Studio 16 2019 MSVC 19.28.29912.0 (Build Engine version 16.9.0+57a23d249 for .NET Framework) | Windows-10.0.17763 | AppVeyor |
1194| Visual Studio 17 2022 MSVC 19.30.30709.0 (Build Engine version 17.0.31804.368 for .NET Framework) | Windows-10.0.20348 | GitHub Actions |
1195
1196
1197## Integration
1198
1199[`json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) is the single required file in `single_include/nlohmann` or [released here](https://github.com/nlohmann/json/releases). You need to add
1200
1201```cpp
1202#include <nlohmann/json.hpp>
1203
1204// for convenience
1205using json = nlohmann::json;
1206```
1207
1208to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., `-std=c++11` for GCC and Clang).
1209
1210You can further use file [`include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/json_fwd.hpp) for forward-declarations. The installation of json_fwd.hpp (as part of cmake's install step), can be achieved by setting `-DJSON_MultipleHeaders=ON`.
1211
1212### CMake
1213
1214You can also use the `nlohmann_json::nlohmann_json` interface target in CMake. This target populates the appropriate usage requirements for `INTERFACE_INCLUDE_DIRECTORIES` to point to the appropriate include directories and `INTERFACE_COMPILE_FEATURES` for the necessary C++11 flags.
1215
1216#### External
1217
1218To use this library from a CMake project, you can locate it directly with `find_package()` and use the namespaced imported target from the generated package configuration:
1219
1220```cmake
1221# CMakeLists.txt
1222find_package(nlohmann_json 3.2.0 REQUIRED)
1223...
1224add_library(foo ...)
1225...
1226target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
1227```
1228
1229The package configuration file, `nlohmann_jsonConfig.cmake`, can be used either from an install tree or directly out of the build tree.
1230
1231#### Embedded
1232
1233To embed the library directly into an existing CMake project, place the entire source tree in a subdirectory and call `add_subdirectory()` in your `CMakeLists.txt` file:
1234
1235```cmake
1236# Typically you don't care so much for a third party library's tests to be
1237# run from your own project's code.
1238set(JSON_BuildTests OFF CACHE INTERNAL "")
1239
1240# If you only include this third party in PRIVATE source files, you do not
1241# need to install it when your main project gets installed.
1242# set(JSON_Install OFF CACHE INTERNAL "")
1243
1244# Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it
1245# unintended consequences that will break the build. It's generally
1246# discouraged (although not necessarily well documented as such) to use
1247# include(...) for pulling in other CMake projects anyways.
1248add_subdirectory(nlohmann_json)
1249...
1250add_library(foo ...)
1251...
1252target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
1253```
1254
1255##### Embedded (FetchContent)
1256
1257Since CMake v3.11,
1258[FetchContent](https://cmake.org/cmake/help/v3.11/module/FetchContent.html) can
1259be used to automatically download a release as a dependency at configure time.
1260
1261Example:
1262```cmake
1263include(FetchContent)
1264
1265FetchContent_Declare(json URL https://github.com/nlohmann/json/releases/download/v3.11.2/json.tar.xz)
1266FetchContent_MakeAvailable(json)
1267
1268target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
1269```
1270
1271**Note**: It is recommended to use the URL approach described above which is supported as of version 3.10.0. See
1272<https://json.nlohmann.me/integration/cmake/#fetchcontent> for more information.
1273
1274#### Supporting Both
1275
1276To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin to the following:
1277
1278``` cmake
1279# Top level CMakeLists.txt
1280project(FOO)
1281...
1282option(FOO_USE_EXTERNAL_JSON "Use an external JSON library" OFF)
1283...
1284add_subdirectory(thirdparty)
1285...
1286add_library(foo ...)
1287...
1288# Note that the namespaced target will always be available regardless of the
1289# import method
1290target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
1291```
1292```cmake
1293# thirdparty/CMakeLists.txt
1294...
1295if(FOO_USE_EXTERNAL_JSON)
1296 find_package(nlohmann_json 3.2.0 REQUIRED)
1297else()
1298 set(JSON_BuildTests OFF CACHE INTERNAL "")
1299 add_subdirectory(nlohmann_json)
1300endif()
1301...
1302```
1303
1304`thirdparty/nlohmann_json` is then a complete copy of this source tree.
1305
1306### Package Managers
1307
1308:beer: If you are using OS X and [Homebrew](https://brew.sh), just type `brew install nlohmann-json` and you're set. If you want the bleeding edge rather than the latest release, use `brew install nlohmann-json --HEAD`. See [nlohmann-json](https://formulae.brew.sh/formula/nlohmann-json) for more information.
1309
1310If you are using the [Meson Build System](https://mesonbuild.com), add this source tree as a [meson subproject](https://mesonbuild.com/Subprojects.html#using-a-subproject). You may also use the `include.zip` published in this project's [Releases](https://github.com/nlohmann/json/releases) to reduce the size of the vendored source tree. Alternatively, you can get a wrap file by downloading it from [Meson WrapDB](https://wrapdb.mesonbuild.com/nlohmann_json), or simply use `meson wrap install nlohmann_json`. Please see the meson project for any issues regarding the packaging.
1311
1312The provided `meson.build` can also be used as an alternative to cmake for installing `nlohmann_json` system-wide in which case a pkg-config file is installed. To use it, simply have your build system require the `nlohmann_json` pkg-config dependency. In Meson, it is preferred to use the [`dependency()`](https://mesonbuild.com/Reference-manual.html#dependency) object with a subproject fallback, rather than using the subproject directly.
1313
1314If you are using [Conan](https://www.conan.io/) to manage your dependencies, merely add [`nlohmann_json/x.y.z`](https://conan.io/center/nlohmann_json) to your `conanfile`'s requires, where `x.y.z` is the release version you want to use. Please file issues [here](https://github.com/conan-io/conan-center-index/issues) if you experience problems with the packages.
1315
1316If you are using [Spack](https://www.spack.io/) to manage your dependencies, you can use the [`nlohmann-json` package](https://spack.readthedocs.io/en/latest/package_list.html#nlohmann-json). Please see the [spack project](https://github.com/spack/spack) for any issues regarding the packaging.
1317
1318If you are using [hunter](https://github.com/cpp-pm/hunter) on your project for external dependencies, then you can use the [nlohmann_json package](https://hunter.readthedocs.io/en/latest/packages/pkg/nlohmann_json.html). Please see the hunter project for any issues regarding the packaging.
1319
1320If you are using [Buckaroo](https://buckaroo.pm), you can install this library's module with `buckaroo add github.com/buckaroo-pm/nlohmann-json`. Please file issues [here](https://github.com/buckaroo-pm/nlohmann-json). There is a demo repo [here](https://github.com/njlr/buckaroo-nholmann-json-example).
1321
1322If you are using [vcpkg](https://github.com/Microsoft/vcpkg/) on your project for external dependencies, then you can install the [nlohmann-json package](https://github.com/Microsoft/vcpkg/tree/master/ports/nlohmann-json) with `vcpkg install nlohmann-json` and follow the then displayed descriptions. Please see the vcpkg project for any issues regarding the packaging.
1323
1324If you are using [cget](https://cget.readthedocs.io/en/latest/), you can install the latest development version with `cget install nlohmann/json`. A specific version can be installed with `cget install nlohmann/json@v3.1.0`. Also, the multiple header version can be installed by adding the `-DJSON_MultipleHeaders=ON` flag (i.e., `cget install nlohmann/json -DJSON_MultipleHeaders=ON`).
1325
1326If you are using [CocoaPods](https://cocoapods.org), you can use the library by adding pod `"nlohmann_json", '~>3.1.2'` to your podfile (see [an example](https://bitbucket.org/benman/nlohmann_json-cocoapod/src/master/)). Please file issues [here](https://bitbucket.org/benman/nlohmann_json-cocoapod/issues?status=new&status=open).
1327
1328If you are using [NuGet](https://www.nuget.org), you can use the package [nlohmann.json](https://www.nuget.org/packages/nlohmann.json/). Please check [this extensive description](https://github.com/nlohmann/json/issues/1132#issuecomment-452250255) on how to use the package. Please file issues [here](https://github.com/hnkb/nlohmann-json-nuget/issues).
1329
1330If you are using [conda](https://conda.io/), you can use the package [nlohmann_json](https://github.com/conda-forge/nlohmann_json-feedstock) from [conda-forge](https://conda-forge.org) executing `conda install -c conda-forge nlohmann_json`. Please file issues [here](https://github.com/conda-forge/nlohmann_json-feedstock/issues).
1331
1332If you are using [MSYS2](https://www.msys2.org/), you can use the [mingw-w64-nlohmann-json](https://packages.msys2.org/base/mingw-w64-nlohmann-json) package, just type `pacman -S mingw-w64-i686-nlohmann-json` or `pacman -S mingw-w64-x86_64-nlohmann-json` for installation. Please file issues [here](https://github.com/msys2/MINGW-packages/issues/new?title=%5Bnlohmann-json%5D) if you experience problems with the packages.
1333
1334If you are using [MacPorts](https://ports.macports.org), execute `sudo port install nlohmann-json` to install the [nlohmann-json](https://ports.macports.org/port/nlohmann-json/) package.
1335
1336If you are using [`build2`](https://build2.org), you can use the [`nlohmann-json`](https://cppget.org/nlohmann-json) package from the public repository https://cppget.org or directly from the [package's sources repository](https://github.com/build2-packaging/nlohmann-json). In your project's `manifest` file, just add `depends: nlohmann-json` (probably with some [version constraints](https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml#guide-add-remove-deps)). If you are not familiar with using dependencies in `build2`, [please read this introduction](https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml).
1337Please file issues [here](https://github.com/build2-packaging/nlohmann-json) if you experience problems with the packages.
1338
1339If you are using [`wsjcpp`](https://wsjcpp.org), you can use the command `wsjcpp install "https://github.com/nlohmann/json:develop"` to get the latest version. Note you can change the branch ":develop" to an existing tag or another branch.
1340
1341If you are using [`CPM.cmake`](https://github.com/TheLartians/CPM.cmake), you can check this [`example`](https://github.com/TheLartians/CPM.cmake/tree/master/examples/json). After [adding CPM script](https://github.com/TheLartians/CPM.cmake#adding-cpm) to your project, implement the following snippet to your CMake:
1342
1343```cmake
1344CPMAddPackage(
1345 NAME nlohmann_json
1346 GITHUB_REPOSITORY nlohmann/json
1347 VERSION 3.9.1)
1348```
1349
1350### Pkg-config
1351
1352If you are using bare Makefiles, you can use `pkg-config` to generate the include flags that point to where the library is installed:
1353
1354```sh
1355pkg-config nlohmann_json --cflags
1356```
1357
1358Users of the Meson build system will also be able to use a system-wide library, which will be found by `pkg-config`:
1359
1360```meson
1361json = dependency('nlohmann_json', required: true)
1362```
1363
1364
1365## License
1366
1367<img align="right" src="https://opensource.org/trademarks/opensource/OSI-Approved-License-100x137.png">
1368
1369The class is licensed under the [MIT License](https://opensource.org/licenses/MIT):
1370
1371Copyright © 2013-2022 [Niels Lohmann](https://nlohmann.me)
1372
1373Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
1374
1375The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
1376
1377THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
1378
1379* * *
1380
1381The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2008-2009 [Björn Hoehrmann](https://bjoern.hoehrmann.de/) <bjoern@hoehrmann.de>
1382
1383The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2009 [Florian Loitsch](https://florian.loitsch.com/)
1384
1385The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).
1386
1387The class contains parts of [Google Abseil](https://github.com/abseil/abseil-cpp) which is licensed under the [Apache 2.0 License](https://opensource.org/licenses/Apache-2.0).
1388
1389## Contact
1390
1391If you have questions regarding the library, I would like to invite you to [open an issue at GitHub](https://github.com/nlohmann/json/issues/new/choose). Please describe your request, problem, or question as detailed as possible, and also mention the version of the library you are using as well as the version of your compiler and operating system. Opening an issue at GitHub allows other users and contributors to this library to collaborate. For instance, I have little experience with MSVC, and most issues in this regard have been solved by a growing community. If you have a look at the [closed issues](https://github.com/nlohmann/json/issues?q=is%3Aissue+is%3Aclosed), you will see that we react quite timely in most cases.
1392
1393Only if your request would contain confidential information, please [send me an email](mailto:mail@nlohmann.me). For encrypted messages, please use [this key](https://keybase.io/nlohmann/pgp_keys.asc).
1394
1395## Security
1396
1397[Commits by Niels Lohmann](https://github.com/nlohmann/json/commits) and [releases](https://github.com/nlohmann/json/releases) are signed with this [PGP Key](https://keybase.io/nlohmann/pgp_keys.asc?fingerprint=797167ae41c0a6d9232e48457f3cea63ae251b69).
1398
1399## Thanks
1400
1401I deeply appreciate the help of the following people.
1402
1403<img src="https://raw.githubusercontent.com/nlohmann/json/develop/docs/avatars.png" align="right">
1404
14051. [Teemperor](https://github.com/Teemperor) implemented CMake support and lcov integration, realized escape and Unicode handling in the string parser, and fixed the JSON serialization.
14062. [elliotgoodrich](https://github.com/elliotgoodrich) fixed an issue with double deletion in the iterator classes.
14073. [kirkshoop](https://github.com/kirkshoop) made the iterators of the class composable to other libraries.
14084. [wancw](https://github.com/wanwc) fixed a bug that hindered the class to compile with Clang.
14095. Tomas Åblad found a bug in the iterator implementation.
14106. [Joshua C. Randall](https://github.com/jrandall) fixed a bug in the floating-point serialization.
14117. [Aaron Burghardt](https://github.com/aburgh) implemented code to parse streams incrementally. Furthermore, he greatly improved the parser class by allowing the definition of a filter function to discard undesired elements while parsing.
14128. [Daniel Kopeček](https://github.com/dkopecek) fixed a bug in the compilation with GCC 5.0.
14139. [Florian Weber](https://github.com/Florianjw) fixed a bug in and improved the performance of the comparison operators.
141410. [Eric Cornelius](https://github.com/EricMCornelius) pointed out a bug in the handling with NaN and infinity values. He also improved the performance of the string escaping.
141511. [易思龙](https://github.com/likebeta) implemented a conversion from anonymous enums.
141612. [kepkin](https://github.com/kepkin) patiently pushed forward the support for Microsoft Visual studio.
141713. [gregmarr](https://github.com/gregmarr) simplified the implementation of reverse iterators and helped with numerous hints and improvements. In particular, he pushed forward the implementation of user-defined types.
141814. [Caio Luppi](https://github.com/caiovlp) fixed a bug in the Unicode handling.
141915. [dariomt](https://github.com/dariomt) fixed some typos in the examples.
142016. [Daniel Frey](https://github.com/d-frey) cleaned up some pointers and implemented exception-safe memory allocation.
142117. [Colin Hirsch](https://github.com/ColinH) took care of a small namespace issue.
142218. [Huu Nguyen](https://github.com/whoshuu) correct a variable name in the documentation.
142319. [Silverweed](https://github.com/silverweed) overloaded `parse()` to accept an rvalue reference.
142420. [dariomt](https://github.com/dariomt) fixed a subtlety in MSVC type support and implemented the `get_ref()` function to get a reference to stored values.
142521. [ZahlGraf](https://github.com/ZahlGraf) added a workaround that allows compilation using Android NDK.
142622. [whackashoe](https://github.com/whackashoe) replaced a function that was marked as unsafe by Visual Studio.
142723. [406345](https://github.com/406345) fixed two small warnings.
142824. [Glen Fernandes](https://github.com/glenfe) noted a potential portability problem in the `has_mapped_type` function.
142925. [Corbin Hughes](https://github.com/nibroc) fixed some typos in the contribution guidelines.
143026. [twelsby](https://github.com/twelsby) fixed the array subscript operator, an issue that failed the MSVC build, and floating-point parsing/dumping. He further added support for unsigned integer numbers and implemented better roundtrip support for parsed numbers.
143127. [Volker Diels-Grabsch](https://github.com/vog) fixed a link in the README file.
143228. [msm-](https://github.com/msm-) added support for American Fuzzy Lop.
143329. [Annihil](https://github.com/Annihil) fixed an example in the README file.
143430. [Themercee](https://github.com/Themercee) noted a wrong URL in the README file.
143531. [Lv Zheng](https://github.com/lv-zheng) fixed a namespace issue with `int64_t` and `uint64_t`.
143632. [abc100m](https://github.com/abc100m) analyzed the issues with GCC 4.8 and proposed a [partial solution](https://github.com/nlohmann/json/pull/212).
143733. [zewt](https://github.com/zewt) added useful notes to the README file about Android.
143834. [Róbert Márki](https://github.com/robertmrk) added a fix to use move iterators and improved the integration via CMake.
143935. [Chris Kitching](https://github.com/ChrisKitching) cleaned up the CMake files.
144036. [Tom Needham](https://github.com/06needhamt) fixed a subtle bug with MSVC 2015 which was also proposed by [Michael K.](https://github.com/Epidal).
144137. [Mário Feroldi](https://github.com/thelostt) fixed a small typo.
144238. [duncanwerner](https://github.com/duncanwerner) found a really embarrassing performance regression in the 2.0.0 release.
144339. [Damien](https://github.com/dtoma) fixed one of the last conversion warnings.
144440. [Thomas Braun](https://github.com/t-b) fixed a warning in a test case and adjusted MSVC calls in the CI.
144541. [Théo DELRIEU](https://github.com/theodelrieu) patiently and constructively oversaw the long way toward [iterator-range parsing](https://github.com/nlohmann/json/issues/290). He also implemented the magic behind the serialization/deserialization of user-defined types and split the single header file into smaller chunks.
144642. [Stefan](https://github.com/5tefan) fixed a minor issue in the documentation.
144743. [Vasil Dimov](https://github.com/vasild) fixed the documentation regarding conversions from `std::multiset`.
144844. [ChristophJud](https://github.com/ChristophJud) overworked the CMake files to ease project inclusion.
144945. [Vladimir Petrigo](https://github.com/vpetrigo) made a SFINAE hack more readable and added Visual Studio 17 to the build matrix.
145046. [Denis Andrejew](https://github.com/seeekr) fixed a grammar issue in the README file.
145147. [Pierre-Antoine Lacaze](https://github.com/palacaze) found a subtle bug in the `dump()` function.
145248. [TurpentineDistillery](https://github.com/TurpentineDistillery) pointed to [`std::locale::classic()`](https://en.cppreference.com/w/cpp/locale/locale/classic) to avoid too much locale joggling, found some nice performance improvements in the parser, improved the benchmarking code, and realized locale-independent number parsing and printing.
145349. [cgzones](https://github.com/cgzones) had an idea how to fix the Coverity scan.
145450. [Jared Grubb](https://github.com/jaredgrubb) silenced a nasty documentation warning.
145551. [Yixin Zhang](https://github.com/qwename) fixed an integer overflow check.
145652. [Bosswestfalen](https://github.com/Bosswestfalen) merged two iterator classes into a smaller one.
145753. [Daniel599](https://github.com/Daniel599) helped to get Travis execute the tests with Clang's sanitizers.
145854. [Jonathan Lee](https://github.com/vjon) fixed an example in the README file.
145955. [gnzlbg](https://github.com/gnzlbg) supported the implementation of user-defined types.
146056. [Alexej Harm](https://github.com/qis) helped to get the user-defined types working with Visual Studio.
146157. [Jared Grubb](https://github.com/jaredgrubb) supported the implementation of user-defined types.
146258. [EnricoBilla](https://github.com/EnricoBilla) noted a typo in an example.
146359. [Martin Hořeňovský](https://github.com/horenmar) found a way for a 2x speedup for the compilation time of the test suite.
146460. [ukhegg](https://github.com/ukhegg) found proposed an improvement for the examples section.
146561. [rswanson-ihi](https://github.com/rswanson-ihi) noted a typo in the README.
146662. [Mihai Stan](https://github.com/stanmihai4) fixed a bug in the comparison with `nullptr`s.
146763. [Tushar Maheshwari](https://github.com/tusharpm) added [cotire](https://github.com/sakra/cotire) support to speed up the compilation.
146864. [TedLyngmo](https://github.com/TedLyngmo) noted a typo in the README, removed unnecessary bit arithmetic, and fixed some `-Weffc++` warnings.
146965. [Krzysztof Woś](https://github.com/krzysztofwos) made exceptions more visible.
147066. [ftillier](https://github.com/ftillier) fixed a compiler warning.
147167. [tinloaf](https://github.com/tinloaf) made sure all pushed warnings are properly popped.
147268. [Fytch](https://github.com/Fytch) found a bug in the documentation.
147369. [Jay Sistar](https://github.com/Type1J) implemented a Meson build description.
147470. [Henry Lee](https://github.com/HenryRLee) fixed a warning in ICC and improved the iterator implementation.
147571. [Vincent Thiery](https://github.com/vthiery) maintains a package for the Conan package manager.
147672. [Steffen](https://github.com/koemeet) fixed a potential issue with MSVC and `std::min`.
147773. [Mike Tzou](https://github.com/Chocobo1) fixed some typos.
147874. [amrcode](https://github.com/amrcode) noted a misleading documentation about comparison of floats.
147975. [Oleg Endo](https://github.com/olegendo) reduced the memory consumption by replacing `<iostream>` with `<iosfwd>`.
148076. [dan-42](https://github.com/dan-42) cleaned up the CMake files to simplify including/reusing of the library.
148177. [Nikita Ofitserov](https://github.com/himikof) allowed for moving values from initializer lists.
148278. [Greg Hurrell](https://github.com/wincent) fixed a typo.
148379. [Dmitry Kukovinets](https://github.com/DmitryKuk) fixed a typo.
148480. [kbthomp1](https://github.com/kbthomp1) fixed an issue related to the Intel OSX compiler.
148581. [Markus Werle](https://github.com/daixtrose) fixed a typo.
148682. [WebProdPP](https://github.com/WebProdPP) fixed a subtle error in a precondition check.
148783. [Alex](https://github.com/leha-bot) noted an error in a code sample.
148884. [Tom de Geus](https://github.com/tdegeus) reported some warnings with ICC and helped to fix them.
148985. [Perry Kundert](https://github.com/pjkundert) simplified reading from input streams.
149086. [Sonu Lohani](https://github.com/sonulohani) fixed a small compilation error.
149187. [Jamie Seward](https://github.com/jseward) fixed all MSVC warnings.
149288. [Nate Vargas](https://github.com/eld00d) added a Doxygen tag file.
149389. [pvleuven](https://github.com/pvleuven) helped to fix a warning in ICC.
149490. [Pavel](https://github.com/crea7or) helped to fix some warnings in MSVC.
149591. [Jamie Seward](https://github.com/jseward) avoided unnecessary string copies in `find()` and `count()`.
149692. [Mitja](https://github.com/Itja) fixed some typos.
149793. [Jorrit Wronski](https://github.com/jowr) updated the Hunter package links.
149894. [Matthias Möller](https://github.com/TinyTinni) added a `.natvis` for the MSVC debug view.
149995. [bogemic](https://github.com/bogemic) fixed some C++17 deprecation warnings.
150096. [Eren Okka](https://github.com/erengy) fixed some MSVC warnings.
150197. [abolz](https://github.com/abolz) integrated the Grisu2 algorithm for proper floating-point formatting, allowing more roundtrip checks to succeed.
150298. [Vadim Evard](https://github.com/Pipeliner) fixed a Markdown issue in the README.
150399. [zerodefect](https://github.com/zerodefect) fixed a compiler warning.
1504100. [Kert](https://github.com/kaidokert) allowed to template the string type in the serialization and added the possibility to override the exceptional behavior.
1505101. [mark-99](https://github.com/mark-99) helped fixing an ICC error.
1506102. [Patrik Huber](https://github.com/patrikhuber) fixed links in the README file.
1507103. [johnfb](https://github.com/johnfb) found a bug in the implementation of CBOR's indefinite length strings.
1508104. [Paul Fultz II](https://github.com/pfultz2) added a note on the cget package manager.
1509105. [Wilson Lin](https://github.com/wla80) made the integration section of the README more concise.
1510106. [RalfBielig](https://github.com/ralfbielig) detected and fixed a memory leak in the parser callback.
1511107. [agrianius](https://github.com/agrianius) allowed to dump JSON to an alternative string type.
1512108. [Kevin Tonon](https://github.com/ktonon) overworked the C++11 compiler checks in CMake.
1513109. [Axel Huebl](https://github.com/ax3l) simplified a CMake check and added support for the [Spack package manager](https://spack.io).
1514110. [Carlos O'Ryan](https://github.com/coryan) fixed a typo.
1515111. [James Upjohn](https://github.com/jammehcow) fixed a version number in the compilers section.
1516112. [Chuck Atkins](https://github.com/chuckatkins) adjusted the CMake files to the CMake packaging guidelines and provided documentation for the CMake integration.
1517113. [Jan Schöppach](https://github.com/dns13) fixed a typo.
1518114. [martin-mfg](https://github.com/martin-mfg) fixed a typo.
1519115. [Matthias Möller](https://github.com/TinyTinni) removed the dependency from `std::stringstream`.
1520116. [agrianius](https://github.com/agrianius) added code to use alternative string implementations.
1521117. [Daniel599](https://github.com/Daniel599) allowed to use more algorithms with the `items()` function.
1522118. [Julius Rakow](https://github.com/jrakow) fixed the Meson include directory and fixed the links to [cppreference.com](cppreference.com).
1523119. [Sonu Lohani](https://github.com/sonulohani) fixed the compilation with MSVC 2015 in debug mode.
1524120. [grembo](https://github.com/grembo) fixed the test suite and re-enabled several test cases.
1525121. [Hyeon Kim](https://github.com/simnalamburt) introduced the macro `JSON_INTERNAL_CATCH` to control the exception handling inside the library.
1526122. [thyu](https://github.com/thyu) fixed a compiler warning.
1527123. [David Guthrie](https://github.com/LEgregius) fixed a subtle compilation error with Clang 3.4.2.
1528124. [Dennis Fischer](https://github.com/dennisfischer) allowed to call `find_package` without installing the library.
1529125. [Hyeon Kim](https://github.com/simnalamburt) fixed an issue with a double macro definition.
1530126. [Ben Berman](https://github.com/rivertam) made some error messages more understandable.
1531127. [zakalibit](https://github.com/zakalibit) fixed a compilation problem with the Intel C++ compiler.
1532128. [mandreyel](https://github.com/mandreyel) fixed a compilation problem.
1533129. [Kostiantyn Ponomarenko](https://github.com/koponomarenko) added version and license information to the Meson build file.
1534130. [Henry Schreiner](https://github.com/henryiii) added support for GCC 4.8.
1535131. [knilch](https://github.com/knilch0r) made sure the test suite does not stall when run in the wrong directory.
1536132. [Antonio Borondo](https://github.com/antonioborondo) fixed an MSVC 2017 warning.
1537133. [Dan Gendreau](https://github.com/dgendreau) implemented the `NLOHMANN_JSON_SERIALIZE_ENUM` macro to quickly define an enum/JSON mapping.
1538134. [efp](https://github.com/efp) added line and column information to parse errors.
1539135. [julian-becker](https://github.com/julian-becker) added BSON support.
1540136. [Pratik Chowdhury](https://github.com/pratikpc) added support for structured bindings.
1541137. [David Avedissian](https://github.com/davedissian) added support for Clang 5.0.1 (PS4 version).
1542138. [Jonathan Dumaresq](https://github.com/dumarjo) implemented an input adapter to read from `FILE*`.
1543139. [kjpus](https://github.com/kjpus) fixed a link in the documentation.
1544140. [Manvendra Singh](https://github.com/manu-chroma) fixed a typo in the documentation.
1545141. [ziggurat29](https://github.com/ziggurat29) fixed an MSVC warning.
1546142. [Sylvain Corlay](https://github.com/SylvainCorlay) added code to avoid an issue with MSVC.
1547143. [mefyl](https://github.com/mefyl) fixed a bug when JSON was parsed from an input stream.
1548144. [Millian Poquet](https://github.com/mpoquet) allowed to install the library via Meson.
1549145. [Michael Behrns-Miller](https://github.com/moodboom) found an issue with a missing namespace.
1550146. [Nasztanovics Ferenc](https://github.com/naszta) fixed a compilation issue with libc 2.12.
1551147. [Andreas Schwab](https://github.com/andreas-schwab) fixed the endian conversion.
1552148. [Mark-Dunning](https://github.com/Mark-Dunning) fixed a warning in MSVC.
1553149. [Gareth Sylvester-Bradley](https://github.com/garethsb-sony) added `operator/` for JSON Pointers.
1554150. [John-Mark](https://github.com/johnmarkwayve) noted a missing header.
1555151. [Vitaly Zaitsev](https://github.com/xvitaly) fixed compilation with GCC 9.0.
1556152. [Laurent Stacul](https://github.com/stac47) fixed compilation with GCC 9.0.
1557153. [Ivor Wanders](https://github.com/iwanders) helped to reduce the CMake requirement to version 3.1.
1558154. [njlr](https://github.com/njlr) updated the Buckaroo instructions.
1559155. [Lion](https://github.com/lieff) fixed a compilation issue with GCC 7 on CentOS.
1560156. [Isaac Nickaein](https://github.com/nickaein) improved the integer serialization performance and implemented the `contains()` function.
1561157. [past-due](https://github.com/past-due) suppressed an unfixable warning.
1562158. [Elvis Oric](https://github.com/elvisoric) improved Meson support.
1563159. [Matěj Plch](https://github.com/Afforix) fixed an example in the README.
1564160. [Mark Beckwith](https://github.com/wythe) fixed a typo.
1565161. [scinart](https://github.com/scinart) fixed bug in the serializer.
1566162. [Patrick Boettcher](https://github.com/pboettch) implemented `push_back()` and `pop_back()` for JSON Pointers.
1567163. [Bruno Oliveira](https://github.com/nicoddemus) added support for Conda.
1568164. [Michele Caini](https://github.com/skypjack) fixed links in the README.
1569165. [Hani](https://github.com/hnkb) documented how to install the library with NuGet.
1570166. [Mark Beckwith](https://github.com/wythe) fixed a typo.
1571167. [yann-morin-1998](https://github.com/yann-morin-1998) helped to reduce the CMake requirement to version 3.1.
1572168. [Konstantin Podsvirov](https://github.com/podsvirov) maintains a package for the MSYS2 software distro.
1573169. [remyabel](https://github.com/remyabel) added GNUInstallDirs to the CMake files.
1574170. [Taylor Howard](https://github.com/taylorhoward92) fixed a unit test.
1575171. [Gabe Ron](https://github.com/Macr0Nerd) implemented the `to_string` method.
1576172. [Watal M. Iwasaki](https://github.com/heavywatal) fixed a Clang warning.
1577173. [Viktor Kirilov](https://github.com/onqtam) switched the unit tests from [Catch](https://github.com/philsquared/Catch) to [doctest](https://github.com/onqtam/doctest)
1578174. [Juncheng E](https://github.com/ejcjason) fixed a typo.
1579175. [tete17](https://github.com/tete17) fixed a bug in the `contains` function.
1580176. [Xav83](https://github.com/Xav83) fixed some cppcheck warnings.
1581177. [0xflotus](https://github.com/0xflotus) fixed some typos.
1582178. [Christian Deneke](https://github.com/chris0x44) added a const version of `json_pointer::back`.
1583179. [Julien Hamaide](https://github.com/crazyjul) made the `items()` function work with custom string types.
1584180. [Evan Nemerson](https://github.com/nemequ) updated fixed a bug in Hedley and updated this library accordingly.
1585181. [Florian Pigorsch](https://github.com/flopp) fixed a lot of typos.
1586182. [Camille Bégué](https://github.com/cbegue) fixed an issue in the conversion from `std::pair` and `std::tuple` to `json`.
1587183. [Anthony VH](https://github.com/AnthonyVH) fixed a compile error in an enum deserialization.
1588184. [Yuriy Vountesmery](https://github.com/ua-code-dragon) noted a subtle bug in a preprocessor check.
1589185. [Chen](https://github.com/dota17) fixed numerous issues in the library.
1590186. [Antony Kellermann](https://github.com/aokellermann) added a CI step for GCC 10.1.
1591187. [Alex](https://github.com/gistrec) fixed an MSVC warning.
1592188. [Rainer](https://github.com/rvjr) proposed an improvement in the floating-point serialization in CBOR.
1593189. [Francois Chabot](https://github.com/FrancoisChabot) made performance improvements in the input adapters.
1594190. [Arthur Sonzogni](https://github.com/ArthurSonzogni) documented how the library can be included via `FetchContent`.
1595191. [Rimas Misevičius](https://github.com/rmisev) fixed an error message.
1596192. [Alexander Myasnikov](https://github.com/alexandermyasnikov) fixed some examples and a link in the README.
1597193. [Hubert Chathi](https://github.com/uhoreg) made CMake's version config file architecture-independent.
1598194. [OmnipotentEntity](https://github.com/OmnipotentEntity) implemented the binary values for CBOR, MessagePack, BSON, and UBJSON.
1599195. [ArtemSarmini](https://github.com/ArtemSarmini) fixed a compilation issue with GCC 10 and fixed a leak.
1600196. [Evgenii Sopov](https://github.com/sea-kg) integrated the library to the wsjcpp package manager.
1601197. [Sergey Linev](https://github.com/linev) fixed a compiler warning.
1602198. [Miguel Magalhães](https://github.com/magamig) fixed the year in the copyright.
1603199. [Gareth Sylvester-Bradley](https://github.com/garethsb-sony) fixed a compilation issue with MSVC.
1604200. [Alexander “weej” Jones](https://github.com/alex-weej) fixed an example in the README.
1605201. [Antoine Cœur](https://github.com/Coeur) fixed some typos in the documentation.
1606202. [jothepro](https://github.com/jothepro) updated links to the Hunter package.
1607203. [Dave Lee](https://github.com/kastiglione) fixed link in the README.
1608204. [Joël Lamotte](https://github.com/Klaim) added instruction for using Build2's package manager.
1609205. [Paul Jurczak](https://github.com/pauljurczak) fixed an example in the README.
1610206. [Sonu Lohani](https://github.com/sonulohani) fixed a warning.
1611207. [Carlos Gomes Martinho](https://github.com/gocarlos) updated the Conan package source.
1612208. [Konstantin Podsvirov](https://github.com/podsvirov) fixed the MSYS2 package documentation.
1613209. [Tridacnid](https://github.com/Tridacnid) improved the CMake tests.
1614210. [Michael](https://github.com/MBalszun) fixed MSVC warnings.
1615211. [Quentin Barbarat](https://github.com/quentin-dev) fixed an example in the documentation.
1616212. [XyFreak](https://github.com/XyFreak) fixed a compiler warning.
1617213. [TotalCaesar659](https://github.com/TotalCaesar659) fixed links in the README.
1618214. [Tanuj Garg](https://github.com/tanuj208) improved the fuzzer coverage for UBSAN input.
1619215. [AODQ](https://github.com/AODQ) fixed a compiler warning.
1620216. [jwittbrodt](https://github.com/jwittbrodt) made `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` inline.
1621217. [pfeatherstone](https://github.com/pfeatherstone) improved the upper bound of arguments of the `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`/`NLOHMANN_DEFINE_TYPE_INTRUSIVE` macros.
1622218. [Jan Procházka](https://github.com/jprochazk) fixed a bug in the CBOR parser for binary and string values.
1623219. [T0b1-iOS](https://github.com/T0b1-iOS) fixed a bug in the new hash implementation.
1624220. [Matthew Bauer](https://github.com/matthewbauer) adjusted the CBOR writer to create tags for binary subtypes.
1625221. [gatopeich](https://github.com/gatopeich) implemented an ordered map container for `nlohmann::ordered_json`.
1626222. [Érico Nogueira Rolim](https://github.com/ericonr) added support for pkg-config.
1627223. [KonanM](https://github.com/KonanM) proposed an implementation for the `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`/`NLOHMANN_DEFINE_TYPE_INTRUSIVE` macros.
1628224. [Guillaume Racicot](https://github.com/gracicot) implemented `string_view` support and allowed C++20 support.
1629225. [Alex Reinking](https://github.com/alexreinking) improved CMake support for `FetchContent`.
1630226. [Hannes Domani](https://github.com/ssbssa) provided a GDB pretty printer.
1631227. Lars Wirzenius reviewed the README file.
1632228. [Jun Jie](https://github.com/ongjunjie) fixed a compiler path in the CMake scripts.
1633229. [Ronak Buch](https://github.com/rbuch) fixed typos in the documentation.
1634230. [Alexander Karzhenkov](https://github.com/karzhenkov) fixed a move constructor and the Travis builds.
1635231. [Leonardo Lima](https://github.com/leozz37) added CPM.Cmake support.
1636232. [Joseph Blackman](https://github.com/jbzdarkid) fixed a warning.
1637233. [Yaroslav](https://github.com/YarikTH) updated doctest and implemented unit tests.
1638234. [Martin Stump](https://github.com/globberwops) fixed a bug in the CMake files.
1639235. [Jaakko Moisio](https://github.com/jasujm) fixed a bug in the input adapters.
1640236. [bl-ue](https://github.com/bl-ue) fixed some Markdown issues in the README file.
1641237. [William A. Wieselquist](https://github.com/wawiesel) fixed an example from the README.
1642238. [abbaswasim](https://github.com/abbaswasim) fixed an example from the README.
1643239. [Remy Jette](https://github.com/remyjette) fixed a warning.
1644240. [Fraser](https://github.com/frasermarlow) fixed the documentation.
1645241. [Ben Beasley](https://github.com/musicinmybrain) updated doctest.
1646242. [Doron Behar](https://github.com/doronbehar) fixed pkg-config.pc.
1647243. [raduteo](https://github.com/raduteo) fixed a warning.
1648244. [David Pfahler](https://github.com/theShmoo) added the possibility to compile the library without I/O support.
1649245. [Morten Fyhn Amundsen](https://github.com/mortenfyhn) fixed a typo.
1650246. [jpl-mac](https://github.com/jpl-mac) allowed to treat the library as a system header in CMake.
1651247. [Jason Dsouza](https://github.com/jasmcaus) fixed the indentation of the CMake file.
1652248. [offa](https://github.com/offa) added a link to Conan Center to the documentation.
1653249. [TotalCaesar659](https://github.com/TotalCaesar659) updated the links in the documentation to use HTTPS.
1654250. [Rafail Giavrimis](https://github.com/grafail) fixed the Google Benchmark default branch.
1655251. [Louis Dionne](https://github.com/ldionne) fixed a conversion operator.
1656252. [justanotheranonymoususer](https://github.com/justanotheranonymoususer) made the examples in the README more consistent.
1657253. [Finkman](https://github.com/Finkman) suppressed some `-Wfloat-equal` warnings.
1658254. [Ferry Huberts](https://github.com/fhuberts) fixed `-Wswitch-enum` warnings.
1659255. [Arseniy Terekhin](https://github.com/senyai) made the GDB pretty-printer robust against unset variable names.
1660256. [Amir Masoud Abdol](https://github.com/amirmasoudabdol) updated the Homebrew command as nlohmann/json is now in homebrew-core.
1661257. [Hallot](https://github.com/Hallot) fixed some `-Wextra-semi-stmt warnings`.
1662258. [Giovanni Cerretani](https://github.com/gcerretani) fixed `-Wunused` warnings on `JSON_DIAGNOSTICS`.
1663259. [Bogdan Popescu](https://github.com/Kapeli) hosts the [docset](https://github.com/Kapeli/Dash-User-Contributions/tree/master/docsets/JSON_for_Modern_C%2B%2B) for offline documentation viewers.
1664260. [Carl Smedstad](https://github.com/carlsmedstad) fixed an assertion error when using `JSON_DIAGNOSTICS`.
1665261. [miikka75](https://github.com/miikka75) provided an important fix to compile C++17 code with Clang 9.
1666262. [Maarten Becker](https://github.com/kernie) fixed a warning for shadowed variables.
1667263. [Cristi Vîjdea](https://github.com/axnsan12) fixed typos in the `operator[]` documentation.
1668264. [Alex Beregszaszi](https://github.com/axic) fixed spelling mistakes in comments.
1669265. [Dirk Stolle](https://github.com/striezel) fixed typos in documentation.
1670266. [Daniel Albuschat](https://github.com/daniel-kun) corrected the parameter name in the `parse` documentation.
1671267. [Prince Mendiratta](https://github.com/Prince-Mendiratta) fixed a link to the FAQ.
1672268. [Florian Albrechtskirchinger](https://github.com/falbrechtskirchinger) implemented `std::string_view` support for object keys and made dozens of other improvements.
1673269. [Qianqian Fang](https://github.com/fangq) implemented the Binary JData (BJData) format.
1674270. [pketelsen](https://github.com/pketelsen) added macros `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` and `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`.
1675271. [DarkZeros](https://github.com/DarkZeros) adjusted to code to not clash with Arduino defines.
1676272. [flagarde](https://github.com/flagarde) fixed the output of `meta()` for MSVC.
1677273. [Giovanni Cerretani](https://github.com/gcerretani) fixed a check for `std::filesystem`.
1678274. [Dimitris Apostolou](https://github.com/rex4539) fixed a typo.
1679275. [Ferry Huberts](https://github.com/fhuberts) fixed a typo.
1680276. [Michael Nosthoff](https://github.com/heinemml) fixed a typo.
1681277. [JungHoon Lee](https://github.com/jhnlee) fixed a typo.
1682278. [Faruk D.](https://github.com/fdiblen) fixed the CITATION.CFF file.
1683279. [Andrea Cocito](https://github.com/puffetto) added a clarification on macro usage to the documentation.
1684280. [Krzysiek Karbowiak](https://github.com/kkarbowiak) refactored the tests to use `CHECK_THROWS_WITH_AS`.
1685281. [Chaoqi Zhang](https://github.com/prncoprs) fixed a typo.
1686282. [ivanovmp](https://github.com/ivanovmp) fixed a whitespace error.
1687283. [KsaNL](https://github.com/KsaNL) fixed a build error when including `<windows.h>`.
1688284. [Andrea Pappacoda](https://github.com/Tachi107) moved `.pc` and `.cmake` files to `share` directory.
1689285. [Wolf Vollprecht](https://github.com/wolfv) added the `patch_inplace` function.
1690286. [Jake Zimmerman](https://github.com/jez) highlighted common usage patterns in the README file.
1691287. [NN](https://github.com/NN---) added the Visual Studio output directory to `.gitignore`.
1692288. [Romain Reignier](https://github.com/romainreignier) improved the performance the vector output adapter.
1693289. [Mike](https://github.com/Mike-Leo-Smith) fixed the `std::iterator_traits`.
1694290. [Richard Hozák](https://github.com/zxey) added macro `JSON_NO_ENUM` to disable default enum conversions.
1695291. [vakokako](https://github.com/vakokako) fixed tests when compiling with C++20.
1696292. [Alexander “weej” Jones](https://github.com/alexweej) fixed an example in the README.
1697293. [Eli Schwartz](https://github.com/eli-schwartz) added more files to the `include.zip` archive.
1698294. [Kevin Lu](https://github.com/kevinlul) fixed a compilation issue when typedefs with certain names were present.
1699295. [Trevor Hickey](https://github.com/luxe) improved the description of an example.
1700296. [Jef LeCompte](https://github.com/jef) updated the year in the README file.
1701297. [Alexandre Hamez](https://github.com/ahamez) fixed a warning.
1702298. [Maninderpal Badhan](https://github.com/mbadhan) fixed a typo.
1703299. [kevin--](https://github.com/kevin--) added a note to an example in the README file.
1704300. [I](https://github.com/wx257osn2) fixed a typo.
1705301. [Gregorio Litenstein](https://github.com/Lord-Kamina) fixed the Clang detection.
1706302. [Andreas Smas](https://github.com/andoma) added a Doozer badge.
1707303. [WanCW](https://github.com/wancw) fixed the string conversion with Clang.
1708304. [zhaohuaxishi](https://github.com/zhaohuaxishi) fixed a Doxygen error.
1709305. [emvivre](https://github.com/emvivre) removed an invalid parameter from CMake.
1710306. [Tobias Hermann](https://github.com/Dobiasd) fixed a link in the README file.
1711307. [Michael](https://github.com/traits) fixed a warning.
1712308. [Ryan Mulder](https://github.com/ryanjmulder) added `ensure_ascii` to the `dump` function.
1713309. [Muri Nicanor](https://github.com/murinicanor) fixed the `sed` discovery in the Makefile.
1714310. [David Avedissian](https://github.com/dgavedissian) implemented SFINAE-friendly `iterator_traits`.
1715311. [AQNOUCH Mohammed](https://github.com/aqnouch) fixed a typo in the README.
1716312. [Gareth Sylvester-Bradley](https://github.com/garethsb) added `operator/=` and `operator/` to construct JSON pointers.
1717313. [Michael Macnair](https://github.com/mykter) added support for afl-fuzz testing.
1718314. [Berkus Decker](https://github.com/berkus) fixed a typo in the README.
1719315. [Illia Polishchuk](https://github.com/effolkronium) improved the CMake testing.
1720316. [Ikko Ashimine](https://github.com/eltociear) fixed a typo.
1721
1722Thanks a lot for helping out! Please [let me know](mailto:mail@nlohmann.me) if I forgot someone.
1723
1724
1725## Used third-party tools
1726
1727The library itself consists of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of third-party tools and services. Thanks a lot!
1728
1729- [**amalgamate.py - Amalgamate C source and header files**](https://github.com/edlund/amalgamate) to create a single header file
1730- [**American fuzzy lop**](https://lcamtuf.coredump.cx/afl/) for fuzz testing
1731- [**AppVeyor**](https://www.appveyor.com) for [continuous integration](https://ci.appveyor.com/project/nlohmann/json) on Windows
1732- [**Artistic Style**](http://astyle.sourceforge.net) for automatic source code indentation
1733- [**Clang**](https://clang.llvm.org) for compilation with code sanitizers
1734- [**CMake**](https://cmake.org) for build automation
1735- [**Codacy**](https://www.codacy.com) for further [code analysis](https://www.codacy.com/app/nlohmann/json)
1736- [**Coveralls**](https://coveralls.io) to measure [code coverage](https://coveralls.io/github/nlohmann/json)
1737- [**Coverity Scan**](https://scan.coverity.com) for [static analysis](https://scan.coverity.com/projects/nlohmann-json)
1738- [**cppcheck**](http://cppcheck.sourceforge.net) for static analysis
1739- [**doctest**](https://github.com/onqtam/doctest) for the unit tests
1740- [**git-update-ghpages**](https://github.com/rstacruz/git-update-ghpages) to upload the documentation to gh-pages
1741- [**GitHub Changelog Generator**](https://github.com/skywinder/github-changelog-generator) to generate the [ChangeLog](https://github.com/nlohmann/json/blob/develop/ChangeLog.md)
1742- [**Google Benchmark**](https://github.com/google/benchmark) to implement the benchmarks
1743- [**Hedley**](https://nemequ.github.io/hedley/) to avoid re-inventing several compiler-agnostic feature macros
1744- [**lcov**](http://ltp.sourceforge.net/coverage/lcov.php) to process coverage information and create an HTML view
1745- [**libFuzzer**](https://llvm.org/docs/LibFuzzer.html) to implement fuzz testing for OSS-Fuzz
1746- [**Material for MkDocs**](https://squidfunk.github.io/mkdocs-material/) for the style of the documentation site
1747- [**MkDocs**](https://www.mkdocs.org) for the documentation site
1748- [**OSS-Fuzz**](https://github.com/google/oss-fuzz) for continuous fuzz testing of the library ([project repository](https://github.com/google/oss-fuzz/tree/master/projects/json))
1749- [**Probot**](https://probot.github.io) for automating maintainer tasks such as closing stale issues, requesting missing information, or detecting toxic comments.
1750- [**Valgrind**](https://valgrind.org) to check for correct memory management
1751
1752
1753## Projects using JSON for Modern C++
1754
1755The library is currently used in Apple macOS Sierra-Monterey and iOS 10-15. I am not sure what they are using the library for, but I am happy that it runs on so many devices.
1756
1757
1758## Notes
1759
1760### Character encoding
1761
1762The library supports **Unicode input** as follows:
1763
1764- Only **UTF-8** encoded input is supported which is the default encoding for JSON according to [RFC 8259](https://tools.ietf.org/html/rfc8259.html#section-8.1).
1765- `std::u16string` and `std::u32string` can be parsed, assuming UTF-16 and UTF-32 encoding, respectively. These encodings are not supported when reading from files or other input containers.
1766- Other encodings such as Latin-1 or ISO 8859-1 are **not** supported and will yield parse or serialization errors.
1767- [Unicode noncharacters](https://www.unicode.org/faq/private_use.html#nonchar1) will not be replaced by the library.
1768- Invalid surrogates (e.g., incomplete pairs such as `\uDEAD`) will yield parse errors.
1769- The strings stored in the library are UTF-8 encoded. When using the default string type (`std::string`), note that its length/size functions return the number of stored bytes rather than the number of characters or glyphs.
1770- When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace` or `json::error_handler_t::ignore` are used as error handlers.
1771- To store wide strings (e.g., `std::wstring`), you need to convert them to a UTF-8 encoded `std::string` before, see [an example](https://json.nlohmann.me/home/faq/#wide-string-handling).
1772
1773### Comments in JSON
1774
1775This library does not support comments by default. It does so for three reasons:
1776
17771. Comments are not part of the [JSON specification](https://tools.ietf.org/html/rfc8259). You may argue that `//` or `/* */` are allowed in JavaScript, but JSON is not JavaScript.
17782. This was not an oversight: Douglas Crockford [wrote on this](https://plus.google.com/118095276221607585885/posts/RK8qyGVaGSr) in May 2012:
1779
1780 > I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn't.
1781
1782 > Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin before handing it to your JSON parser.
1783
17843. It is dangerous for interoperability if some libraries would add comment support while others don't. Please check [The Harmful Consequences of the Robustness Principle](https://tools.ietf.org/html/draft-iab-protocol-maintenance-01) on this.
1785
1786However, you can pass set parameter `ignore_comments` to true in the `parse` function to ignore `//` or `/* */` comments. Comments will then be treated as whitespace.
1787
1788### Order of object keys
1789
1790By default, the library does not preserve the **insertion order of object elements**. This is standards-compliant, as the [JSON standard](https://tools.ietf.org/html/rfc8259.html) defines objects as "an unordered collection of zero or more name/value pairs".
1791
1792If you do want to preserve the insertion order, you can try the type [`nlohmann::ordered_json`](https://github.com/nlohmann/json/issues/2179). Alternatively, you can use a more sophisticated ordered map like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).
1793
1794### Memory Release
1795
1796We checked with Valgrind and the Address Sanitizer (ASAN) that there are no memory leaks.
1797
1798If you find that a parsing program with this library does not release memory, please consider the following case, and it may be unrelated to this library.
1799
1800**Your program is compiled with glibc.** There is a tunable threshold that glibc uses to decide whether to actually return memory to the system or whether to cache it for later reuse. If in your program you make lots of small allocations and those small allocations are not a contiguous block and are presumably below the threshold, then they will not get returned to the OS.
1801Here is a related issue [#1924](https://github.com/nlohmann/json/issues/1924).
1802
1803### Further notes
1804
1805- The code contains numerous debug **assertions** which can be switched off by defining the preprocessor macro `NDEBUG`, see the [documentation of `assert`](https://en.cppreference.com/w/cpp/error/assert). In particular, note [`operator[]`](https://json.nlohmann.me/api/basic_json/operator%5B%5D/) implements **unchecked access** for const objects: If the given key is not present, the behavior is undefined (think of a dereferenced null pointer) and yields an [assertion failure](https://github.com/nlohmann/json/issues/289) if assertions are switched on. If you are not sure whether an element in an object exists, use checked access with the [`at()` function](https://json.nlohmann.me/api/basic_json/at/). Furthermore, you can define `JSON_ASSERT(x)` to replace calls to `assert(x)`.
1806- As the exact number type is not defined in the [JSON specification](https://tools.ietf.org/html/rfc8259.html), this library tries to choose the best fitting C++ number type automatically. As a result, the type `double` may be used to store numbers which may yield [**floating-point exceptions**](https://github.com/nlohmann/json/issues/181) in certain rare situations if floating-point exceptions have been unmasked in the calling code. These exceptions are not caused by the library and need to be fixed in the calling code, such as by re-masking the exceptions prior to calling library functions.
1807- The code can be compiled without C++ **runtime type identification** features; that is, you can use the `-fno-rtti` compiler flag.
1808- **Exceptions** are used widely within the library. They can, however, be switched off with either using the compiler flag `-fno-exceptions` or by defining the symbol `JSON_NOEXCEPTION`. In this case, exceptions are replaced by `abort()` calls. You can further control this behavior by defining `JSON_THROW_USER` (overriding `throw`), `JSON_TRY_USER` (overriding `try`), and `JSON_CATCH_USER` (overriding `catch`). Note that `JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior. Note the explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not available for MSVC if exceptions are disabled, see [#2824](https://github.com/nlohmann/json/discussions/2824).
1809
1810## Execute unit tests
1811
1812To compile and run the tests, you need to execute
1813
1814```sh
1815$ mkdir build
1816$ cd build
1817$ cmake .. -DJSON_BuildTests=On
1818$ cmake --build .
1819$ ctest --output-on-failure
1820```
1821
1822Note that during the `ctest` stage, several JSON test files are downloaded from an [external repository](https://github.com/nlohmann/json_test_data). If policies forbid downloading artifacts during testing, you can download the files yourself and pass the directory with the test files via `-DJSON_TestDataDirectory=path` to CMake. Then, no Internet connectivity is required. See [issue #2189](https://github.com/nlohmann/json/issues/2189) for more information.
1823
1824If the test suite is not found, several test suites will fail like this:
1825
1826```
1827===============================================================================
1828json/tests/src/make_test_data_available.hpp:21:
1829TEST CASE: check test suite is downloaded
1830
1831json/tests/src/make_test_data_available.hpp:23: FATAL ERROR: REQUIRE( utils::check_testsuite_downloaded() ) is NOT correct!
1832 values: REQUIRE( false )
1833 logged: Test data not found in 'json/cmake-build-debug/json_test_data'.
1834 Please execute target 'download_test_data' before running this test suite.
1835 See <https://github.com/nlohmann/json#execute-unit-tests> for more information.
1836
1837===============================================================================
1838```
1839
1840In case you have downloaded the library rather than checked out the code via Git, test `cmake_fetch_content_configure` will fail. Please execute `ctest -LE git_required` to skip these tests. See [issue #2189](https://github.com/nlohmann/json/issues/2189) for more information.
1841
1842Some tests change the installed files and hence make the whole process not reproducible. Please execute `ctest -LE not_reproducible` to skip these tests. See [issue #2324](https://github.com/nlohmann/json/issues/2324) for more information.
1843
1844Note you need to call `cmake -LE "not_reproducible|git_required"` to exclude both labels. See [issue #2596](https://github.com/nlohmann/json/issues/2596) for more information.
1845
1846As Intel compilers use unsafe floating point optimization by default, the unit tests may fail. Use flag [`/fp:precise`](https://software.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/compiler-reference/compiler-options/compiler-option-details/floating-point-options/fp-model-fp.html) then.
1847
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