1[](https://github.com/nlohmann/json/releases) 2 3[](https://app.travis-ci.com/nlohmann/json) 4[](https://ci.appveyor.com/project/nlohmann/json) 5[](https://github.com/nlohmann/json/actions?query=workflow%3AUbuntu) 6[](https://github.com/nlohmann/json/actions?query=workflow%3AmacOS) 7[](https://github.com/nlohmann/json/actions?query=workflow%3AWindows) 8[](https://coveralls.io/github/nlohmann/json?branch=develop) 9[](https://scan.coverity.com/projects/nlohmann-json) 10[](https://www.codacy.com/gh/nlohmann/json/dashboard?utm_source=github.com&utm_medium=referral&utm_content=nlohmann/json&utm_campaign=Badge_Grade) 11[](https://lgtm.com/projects/g/nlohmann/json/context:cpp) 12[](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:json) 13[](https://wandbox.org/permlink/3lCHrFUZANONKv7a) 14[](https://nlohmann.github.io/json/doxygen/index.html) 15[](https://raw.githubusercontent.com/nlohmann/json/master/LICENSE.MIT) 16[](https://github.com/nlohmann/json/releases) 17[](https://github.com/nlohmann/json/releases) 18[](https://github.com/nlohmann/json/issues) 19[](https://isitmaintained.com/project/nlohmann/json "Average time to resolve an issue") 20[](https://bestpractices.coreinfrastructure.org/projects/289) 21[](https://github.com/sponsors/nlohmann) 22 23- [Design goals](#design-goals) 24- [Sponsors](#sponsors) 25- [Support](#support) ([documentation](https://json.nlohmann.me), [FAQ](http://127.0.0.1:8000/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)) 26- [Examples](#examples) 27 - [JSON as first-class data type](#json-as-first-class-data-type) 28 - [Serialization / Deserialization](#serialization--deserialization) 29 - [STL-like access](#stl-like-access) 30 - [Conversion from STL containers](#conversion-from-stl-containers) 31 - [JSON Pointer and JSON Patch](#json-pointer-and-json-patch) 32 - [JSON Merge Patch](#json-merge-patch) 33 - [Implicit conversions](#implicit-conversions) 34 - [Conversions to/from arbitrary types](#arbitrary-types-conversions) 35 - [Specializing enum conversion](#specializing-enum-conversion) 36 - [Binary formats (BSON, CBOR, MessagePack, and UBJSON)](#binary-formats-bson-cbor-messagepack-and-ubjson) 37- [Supported compilers](#supported-compilers) 38- [Integration](#integration) 39 - [CMake](#cmake) 40 - [Package Managers](#package-managers) 41 - [Pkg-config](#pkg-config) 42- [License](#license) 43- [Contact](#contact) 44- [Thanks](#thanks) 45- [Used third-party tools](#used-third-party-tools) 46- [Projects using JSON for Modern C++](#projects-using-json-for-modern-c) 47- [Notes](#notes) 48- [Execute unit tests](#execute-unit-tests) 49 50## Design goals 51 52There 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: 53 54- **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. 55 56- **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. 57 58- **Serious testing**. Our class is heavily [unit-tested](https://github.com/nlohmann/json/tree/develop/test/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). 59 60Other aspects were not so important to us: 61 62- **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. 63 64- **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. 65 66See the [contribution guidelines](https://github.com/nlohmann/json/blob/master/.github/CONTRIBUTING.md#please-dont) for more information. 67 68 69## Sponsors 70 71You can sponsor this library at [GitHub Sponsors](https://github.com/sponsors/nlohmann). 72 73### :label: Named Sponsors 74 75- [Michael Hartmann](https://github.com/reFX-Mike) 76- [Stefan Hagen](https://github.com/sthagen) 77- [Steve Sperandeo](https://github.com/homer6) 78- [Robert Jefe Lindstädt](https://github.com/eljefedelrodeodeljefe) 79- [Steve Wagner](https://github.com/ciroque) 80 81Thanks everyone! 82 83## Support 84 85: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. 86 87: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/doc/examples), or browse through the [**help pages**](https://json.nlohmann.me). 88 89:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/) or the [**Doxygen documentation**](https://json.nlohmann.me/doxygen/index.html). 90 91: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 many information as possible to help us understand and reproduce your issue. 92 93 94## Examples 95 96Beside the examples below, you may want to check the [documentation](https://nlohmann.github.io/json/) where each function contains a separate code example (e.g., check out [`emplace()`](https://nlohmann.github.io/json/api/basic_json/emplace/)). All [example files](https://github.com/nlohmann/json/tree/develop/doc/examples) can be compiled and executed on their own (e.g., file [emplace.cpp](https://github.com/nlohmann/json/blob/develop/doc/examples/emplace.cpp)). 97 98### JSON as first-class data type 99 100Here are some examples to give you an idea how to use the class. 101 102Assume you want to create the JSON object 103 104```json 105{ 106 "pi": 3.141, 107 "happy": true, 108 "name": "Niels", 109 "nothing": null, 110 "answer": { 111 "everything": 42 112 }, 113 "list": [1, 0, 2], 114 "object": { 115 "currency": "USD", 116 "value": 42.99 117 } 118} 119``` 120 121With this library, you could write: 122 123```cpp 124// create an empty structure (null) 125json j; 126 127// add a number that is stored as double (note the implicit conversion of j to an object) 128j["pi"] = 3.141; 129 130// add a Boolean that is stored as bool 131j["happy"] = true; 132 133// add a string that is stored as std::string 134j["name"] = "Niels"; 135 136// add another null object by passing nullptr 137j["nothing"] = nullptr; 138 139// add an object inside the object 140j["answer"]["everything"] = 42; 141 142// add an array that is stored as std::vector (using an initializer list) 143j["list"] = { 1, 0, 2 }; 144 145// add another object (using an initializer list of pairs) 146j["object"] = { {"currency", "USD"}, {"value", 42.99} }; 147 148// instead, you could also write (which looks very similar to the JSON above) 149json j2 = { 150 {"pi", 3.141}, 151 {"happy", true}, 152 {"name", "Niels"}, 153 {"nothing", nullptr}, 154 {"answer", { 155 {"everything", 42} 156 }}, 157 {"list", {1, 0, 2}}, 158 {"object", { 159 {"currency", "USD"}, 160 {"value", 42.99} 161 }} 162}; 163``` 164 165Note 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://nlohmann.github.io/json/api/basic_json/array/) and [`json::object()`](https://nlohmann.github.io/json/api/basic_json/object/) will help: 166 167```cpp 168// a way to express the empty array [] 169json empty_array_explicit = json::array(); 170 171// ways to express the empty object {} 172json empty_object_implicit = json({}); 173json empty_object_explicit = json::object(); 174 175// a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]] 176json array_not_object = json::array({ {"currency", "USD"}, {"value", 42.99} }); 177``` 178 179### Serialization / Deserialization 180 181#### To/from strings 182 183You can create a JSON value (deserialization) by appending `_json` to a string literal: 184 185```cpp 186// create object from string literal 187json j = "{ \"happy\": true, \"pi\": 3.141 }"_json; 188 189// or even nicer with a raw string literal 190auto j2 = R"( 191 { 192 "happy": true, 193 "pi": 3.141 194 } 195)"_json; 196``` 197 198Note that without appending the `_json` suffix, the passed string literal is not parsed, but just used as JSON string value. That is, `json j = "{ \"happy\": true, \"pi\": 3.141 }"` would just store the string `"{ "happy": true, "pi": 3.141 }"` rather than parsing the actual object. 199 200The above example can also be expressed explicitly using [`json::parse()`](https://nlohmann.github.io/json/api/basic_json/parse/): 201 202```cpp 203// parse explicitly 204auto j3 = json::parse(R"({"happy": true, "pi": 3.141})"); 205``` 206 207You can also get a string representation of a JSON value (serialize): 208 209```cpp 210// explicit conversion to string 211std::string s = j.dump(); // {"happy":true,"pi":3.141} 212 213// serialization with pretty printing 214// pass in the amount of spaces to indent 215std::cout << j.dump(4) << std::endl; 216// { 217// "happy": true, 218// "pi": 3.141 219// } 220``` 221 222Note the difference between serialization and assignment: 223 224```cpp 225// store a string in a JSON value 226json j_string = "this is a string"; 227 228// retrieve the string value 229auto cpp_string = j_string.get<std::string>(); 230// retrieve the string value (alternative when an variable already exists) 231std::string cpp_string2; 232j_string.get_to(cpp_string2); 233 234// retrieve the serialized value (explicit JSON serialization) 235std::string serialized_string = j_string.dump(); 236 237// output of original string 238std::cout << cpp_string << " == " << cpp_string2 << " == " << j_string.get<std::string>() << '\n'; 239// output of serialized value 240std::cout << j_string << " == " << serialized_string << std::endl; 241``` 242 243[`.dump()`](https://nlohmann.github.io/json/api/basic_json/dump/) returns the originally stored string value. 244 245Note the library only supports UTF-8. When you store strings with different encodings in the library, calling [`dump()`](https://nlohmann.github.io/json/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. 246 247#### To/from streams (e.g. files, string streams) 248 249You can also use streams to serialize and deserialize: 250 251```cpp 252// deserialize from standard input 253json j; 254std::cin >> j; 255 256// serialize to standard output 257std::cout << j; 258 259// the setw manipulator was overloaded to set the indentation for pretty printing 260std::cout << std::setw(4) << j << std::endl; 261``` 262 263These operators work for any subclasses of `std::istream` or `std::ostream`. Here is the same example with files: 264 265```cpp 266// read a JSON file 267std::ifstream i("file.json"); 268json j; 269i >> j; 270 271// write prettified JSON to another file 272std::ofstream o("pretty.json"); 273o << std::setw(4) << j << std::endl; 274``` 275 276Please 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. 277 278#### Read from iterator range 279 280You 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>`: 281 282```cpp 283std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'}; 284json j = json::parse(v.begin(), v.end()); 285``` 286 287You may leave the iterators for the range [begin, end): 288 289```cpp 290std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'}; 291json j = json::parse(v); 292``` 293 294#### Custom data source 295 296Since the parse function accepts arbitrary iterator ranges, you can provide your own data sources by implementing the `LegacyInputIterator` concept. 297 298```cpp 299struct MyContainer { 300 void advance(); 301 const char& get_current(); 302}; 303 304struct MyIterator { 305 using difference_type = std::ptrdiff_t; 306 using value_type = char; 307 using pointer = const char*; 308 using reference = const char&; 309 using iterator_category = std::input_iterator_tag; 310 311 MyIterator& operator++() { 312 MyContainer.advance(); 313 return *this; 314 } 315 316 bool operator!=(const MyIterator& rhs) const { 317 return rhs.target != target; 318 } 319 320 reference operator*() const { 321 return target.get_current(); 322 } 323 324 MyContainer* target = nullptr; 325}; 326 327MyIterator begin(MyContainer& tgt) { 328 return MyIterator{&tgt}; 329} 330 331MyIterator end(const MyContainer&) { 332 return {}; 333} 334 335void foo() { 336 MyContainer c; 337 json j = json::parse(c); 338} 339``` 340 341#### SAX interface 342 343The library uses a SAX-like interface with the following functions: 344 345```cpp 346// called when null is parsed 347bool null(); 348 349// called when a boolean is parsed; value is passed 350bool boolean(bool val); 351 352// called when a signed or unsigned integer number is parsed; value is passed 353bool number_integer(number_integer_t val); 354bool number_unsigned(number_unsigned_t val); 355 356// called when a floating-point number is parsed; value and original string is passed 357bool number_float(number_float_t val, const string_t& s); 358 359// called when a string is parsed; value is passed and can be safely moved away 360bool string(string_t& val); 361// called when a binary value is parsed; value is passed and can be safely moved away 362bool binary(binary_t& val); 363 364// called when an object or array begins or ends, resp. The number of elements is passed (or -1 if not known) 365bool start_object(std::size_t elements); 366bool end_object(); 367bool start_array(std::size_t elements); 368bool end_array(); 369// called when an object key is parsed; value is passed and can be safely moved away 370bool key(string_t& val); 371 372// called when a parse error occurs; byte position, the last token, and an exception is passed 373bool parse_error(std::size_t position, const std::string& last_token, const detail::exception& ex); 374``` 375 376The return value of each function determines whether parsing should proceed. 377 378To implement your own SAX handler, proceed as follows: 379 3801. 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. 3812. Create an object of your SAX interface class, e.g. `my_sax`. 3823. 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. 383 384Note 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). 385 386### STL-like access 387 388We 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. 389 390```cpp 391// create an array using push_back 392json j; 393j.push_back("foo"); 394j.push_back(1); 395j.push_back(true); 396 397// also use emplace_back 398j.emplace_back(1.78); 399 400// iterate the array 401for (json::iterator it = j.begin(); it != j.end(); ++it) { 402 std::cout << *it << '\n'; 403} 404 405// range-based for 406for (auto& element : j) { 407 std::cout << element << '\n'; 408} 409 410// getter/setter 411const auto tmp = j[0].get<std::string>(); 412j[1] = 42; 413bool foo = j.at(2); 414 415// comparison 416j == R"(["foo", 1, true, 1.78])"_json; // true 417 418// other stuff 419j.size(); // 4 entries 420j.empty(); // false 421j.type(); // json::value_t::array 422j.clear(); // the array is empty again 423 424// convenience type checkers 425j.is_null(); 426j.is_boolean(); 427j.is_number(); 428j.is_object(); 429j.is_array(); 430j.is_string(); 431 432// create an object 433json o; 434o["foo"] = 23; 435o["bar"] = false; 436o["baz"] = 3.141; 437 438// also use emplace 439o.emplace("weather", "sunny"); 440 441// special iterator member functions for objects 442for (json::iterator it = o.begin(); it != o.end(); ++it) { 443 std::cout << it.key() << " : " << it.value() << "\n"; 444} 445 446// the same code as range for 447for (auto& el : o.items()) { 448 std::cout << el.key() << " : " << el.value() << "\n"; 449} 450 451// even easier with structured bindings (C++17) 452for (auto& [key, value] : o.items()) { 453 std::cout << key << " : " << value << "\n"; 454} 455 456// find an entry 457if (o.contains("foo")) { 458 // there is an entry with key "foo" 459} 460 461// or via find and an iterator 462if (o.find("foo") != o.end()) { 463 // there is an entry with key "foo" 464} 465 466// or simpler using count() 467int foo_present = o.count("foo"); // 1 468int fob_present = o.count("fob"); // 0 469 470// delete an entry 471o.erase("foo"); 472``` 473 474 475### Conversion from STL containers 476 477Any 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. 478 479```cpp 480std::vector<int> c_vector {1, 2, 3, 4}; 481json j_vec(c_vector); 482// [1, 2, 3, 4] 483 484std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6}; 485json j_deque(c_deque); 486// [1.2, 2.3, 3.4, 5.6] 487 488std::list<bool> c_list {true, true, false, true}; 489json j_list(c_list); 490// [true, true, false, true] 491 492std::forward_list<int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543}; 493json j_flist(c_flist); 494// [12345678909876, 23456789098765, 34567890987654, 45678909876543] 495 496std::array<unsigned long, 4> c_array {{1, 2, 3, 4}}; 497json j_array(c_array); 498// [1, 2, 3, 4] 499 500std::set<std::string> c_set {"one", "two", "three", "four", "one"}; 501json j_set(c_set); // only one entry for "one" is used 502// ["four", "one", "three", "two"] 503 504std::unordered_set<std::string> c_uset {"one", "two", "three", "four", "one"}; 505json j_uset(c_uset); // only one entry for "one" is used 506// maybe ["two", "three", "four", "one"] 507 508std::multiset<std::string> c_mset {"one", "two", "one", "four"}; 509json j_mset(c_mset); // both entries for "one" are used 510// maybe ["one", "two", "one", "four"] 511 512std::unordered_multiset<std::string> c_umset {"one", "two", "one", "four"}; 513json j_umset(c_umset); // both entries for "one" are used 514// maybe ["one", "two", "one", "four"] 515``` 516 517Likewise, 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. 518 519```cpp 520std::map<std::string, int> c_map { {"one", 1}, {"two", 2}, {"three", 3} }; 521json j_map(c_map); 522// {"one": 1, "three": 3, "two": 2 } 523 524std::unordered_map<const char*, double> c_umap { {"one", 1.2}, {"two", 2.3}, {"three", 3.4} }; 525json j_umap(c_umap); 526// {"one": 1.2, "two": 2.3, "three": 3.4} 527 528std::multimap<std::string, bool> c_mmap { {"one", true}, {"two", true}, {"three", false}, {"three", true} }; 529json j_mmap(c_mmap); // only one entry for key "three" is used 530// maybe {"one": true, "two": true, "three": true} 531 532std::unordered_multimap<std::string, bool> c_ummap { {"one", true}, {"two", true}, {"three", false}, {"three", true} }; 533json j_ummap(c_ummap); // only one entry for key "three" is used 534// maybe {"one": true, "two": true, "three": true} 535``` 536 537### JSON Pointer and JSON Patch 538 539The 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 to describe differences between two JSON values - effectively allowing patch and diff operations known from Unix. 540 541```cpp 542// a JSON value 543json j_original = R"({ 544 "baz": ["one", "two", "three"], 545 "foo": "bar" 546})"_json; 547 548// access members with a JSON pointer (RFC 6901) 549j_original["/baz/1"_json_pointer]; 550// "two" 551 552// a JSON patch (RFC 6902) 553json j_patch = R"([ 554 { "op": "replace", "path": "/baz", "value": "boo" }, 555 { "op": "add", "path": "/hello", "value": ["world"] }, 556 { "op": "remove", "path": "/foo"} 557])"_json; 558 559// apply the patch 560json j_result = j_original.patch(j_patch); 561// { 562// "baz": "boo", 563// "hello": ["world"] 564// } 565 566// calculate a JSON patch from two JSON values 567json::diff(j_result, j_original); 568// [ 569// { "op":" replace", "path": "/baz", "value": ["one", "two", "three"] }, 570// { "op": "remove","path": "/hello" }, 571// { "op": "add", "path": "/foo", "value": "bar" } 572// ] 573``` 574 575### JSON Merge Patch 576 577The 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. 578 579```cpp 580// a JSON value 581json j_document = R"({ 582 "a": "b", 583 "c": { 584 "d": "e", 585 "f": "g" 586 } 587})"_json; 588 589// a patch 590json j_patch = R"({ 591 "a":"z", 592 "c": { 593 "f": null 594 } 595})"_json; 596 597// apply the patch 598j_document.merge_patch(j_patch); 599// { 600// "a": "z", 601// "c": { 602// "d": "e" 603// } 604// } 605``` 606 607### Implicit conversions 608 609Supported types can be implicitly converted to JSON values. 610 611It is recommended to **NOT USE** implicit conversions **FROM** a JSON value. 612You can find more details about this recommendation [here](https://www.github.com/nlohmann/json/issues/958). 613You 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`. 614 615```cpp 616// strings 617std::string s1 = "Hello, world!"; 618json js = s1; 619auto s2 = js.get<std::string>(); 620// NOT RECOMMENDED 621std::string s3 = js; 622std::string s4; 623s4 = js; 624 625// Booleans 626bool b1 = true; 627json jb = b1; 628auto b2 = jb.get<bool>(); 629// NOT RECOMMENDED 630bool b3 = jb; 631bool b4; 632b4 = jb; 633 634// numbers 635int i = 42; 636json jn = i; 637auto f = jn.get<double>(); 638// NOT RECOMMENDED 639double f2 = jb; 640double f3; 641f3 = jb; 642 643// etc. 644``` 645 646Note that `char` types are not automatically converted to JSON strings, but to integer numbers. A conversion to a string must be specified explicitly: 647 648```cpp 649char ch = 'A'; // ASCII value 65 650json j_default = ch; // stores integer number 65 651json j_string = std::string(1, ch); // stores string "A" 652``` 653 654### Arbitrary types conversions 655 656Every type can be serialized in JSON, not just STL containers and scalar types. Usually, you would do something along those lines: 657 658```cpp 659namespace ns { 660 // a simple struct to model a person 661 struct person { 662 std::string name; 663 std::string address; 664 int age; 665 }; 666} 667 668ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60}; 669 670// convert to JSON: copy each value into the JSON object 671json j; 672j["name"] = p.name; 673j["address"] = p.address; 674j["age"] = p.age; 675 676// ... 677 678// convert from JSON: copy each value from the JSON object 679ns::person p { 680 j["name"].get<std::string>(), 681 j["address"].get<std::string>(), 682 j["age"].get<int>() 683}; 684``` 685 686It works, but that's quite a lot of boilerplate... Fortunately, there's a better way: 687 688```cpp 689// create a person 690ns::person p {"Ned Flanders", "744 Evergreen Terrace", 60}; 691 692// conversion: person -> json 693json j = p; 694 695std::cout << j << std::endl; 696// {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"} 697 698// conversion: json -> person 699auto p2 = j.get<ns::person>(); 700 701// that's it 702assert(p == p2); 703``` 704 705#### Basic usage 706 707To make this work with one of your types, you only need to provide two functions: 708 709```cpp 710using json = nlohmann::json; 711 712namespace ns { 713 void to_json(json& j, const person& p) { 714 j = json{{"name", p.name}, {"address", p.address}, {"age", p.age}}; 715 } 716 717 void from_json(const json& j, person& p) { 718 j.at("name").get_to(p.name); 719 j.at("address").get_to(p.address); 720 j.at("age").get_to(p.age); 721 } 722} // namespace ns 723``` 724 725That's all! When calling the `json` constructor with your type, your custom `to_json` method will be automatically called. 726Likewise, when calling `get<your_type>()` or `get_to(your_type&)`, the `from_json` method will be called. 727 728Some important things: 729 730* 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). 731* 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. 732* 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.) 733* In function `from_json`, use function [`at()`](https://nlohmann.github.io/json/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. 734* You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these. 735 736#### Simplify your life with macros 737 738If you just want to serialize/deserialize some structs, the `to_json`/`from_json` functions can be a lot of boilerplate. 739 740There 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: 741 742- `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)` is to be defined inside of the namespace of the class/struct to create code for. 743- `NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)` is to be defined inside of the class/struct to create code for. This macro can also access private members. 744 745In both macros, the first parameter is the name of the class/struct, and all remaining parameters name the members. 746 747##### Examples 748 749The `to_json`/`from_json` functions for the `person` struct above can be created with: 750 751```cpp 752namespace ns { 753 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, address, age) 754} 755``` 756 757Here is an example with private members, where `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is needed: 758 759```cpp 760namespace ns { 761 class address { 762 private: 763 std::string street; 764 int housenumber; 765 int postcode; 766 767 public: 768 NLOHMANN_DEFINE_TYPE_INTRUSIVE(address, street, housenumber, postcode) 769 }; 770} 771``` 772 773#### How do I convert third-party types? 774 775This requires a bit more advanced technique. But first, let's see how this conversion mechanism works: 776 777The library uses **JSON Serializers** to convert types to json. 778The default serializer for `nlohmann::json` is `nlohmann::adl_serializer` (ADL means [Argument-Dependent Lookup](https://en.cppreference.com/w/cpp/language/adl)). 779 780It is implemented like this (simplified): 781 782```cpp 783template <typename T> 784struct adl_serializer { 785 static void to_json(json& j, const T& value) { 786 // calls the "to_json" method in T's namespace 787 } 788 789 static void from_json(const json& j, T& value) { 790 // same thing, but with the "from_json" method 791 } 792}; 793``` 794 795This 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`... 796 797To solve this, you need to add a specialization of `adl_serializer` to the `nlohmann` namespace, here's an example: 798 799```cpp 800// partial specialization (full specialization works too) 801namespace nlohmann { 802 template <typename T> 803 struct adl_serializer<boost::optional<T>> { 804 static void to_json(json& j, const boost::optional<T>& opt) { 805 if (opt == boost::none) { 806 j = nullptr; 807 } else { 808 j = *opt; // this will call adl_serializer<T>::to_json which will 809 // find the free function to_json in T's namespace! 810 } 811 } 812 813 static void from_json(const json& j, boost::optional<T>& opt) { 814 if (j.is_null()) { 815 opt = boost::none; 816 } else { 817 opt = j.get<T>(); // same as above, but with 818 // adl_serializer<T>::from_json 819 } 820 } 821 }; 822} 823``` 824 825#### How can I use `get()` for non-default constructible/non-copyable types? 826 827There 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: 828 829```cpp 830struct move_only_type { 831 move_only_type() = delete; 832 move_only_type(int ii): i(ii) {} 833 move_only_type(const move_only_type&) = delete; 834 move_only_type(move_only_type&&) = default; 835 836 int i; 837}; 838 839namespace nlohmann { 840 template <> 841 struct adl_serializer<move_only_type> { 842 // note: the return type is no longer 'void', and the method only takes 843 // one argument 844 static move_only_type from_json(const json& j) { 845 return {j.get<int>()}; 846 } 847 848 // Here's the catch! You must provide a to_json method! Otherwise you 849 // will not be able to convert move_only_type to json, since you fully 850 // specialized adl_serializer on that type 851 static void to_json(json& j, move_only_type t) { 852 j = t.i; 853 } 854 }; 855} 856``` 857 858#### Can I write my own serializer? (Advanced use) 859 860Yes. You might want to take a look at [`unit-udt.cpp`](https://github.com/nlohmann/json/blob/develop/test/src/unit-udt.cpp) in the test suite, to see a few examples. 861 862If you write your own serializer, you'll need to do a few things: 863 864- use a different `basic_json` alias than `nlohmann::json` (the last template parameter of `basic_json` is the `JSONSerializer`) 865- use your `basic_json` alias (or a template parameter) in all your `to_json`/`from_json` methods 866- use `nlohmann::to_json` and `nlohmann::from_json` when you need ADL 867 868Here is an example, without simplifications, that only accepts types with a size <= 32, and uses ADL. 869 870```cpp 871// You should use void as a second template argument 872// if you don't need compile-time checks on T 873template<typename T, typename SFINAE = typename std::enable_if<sizeof(T) <= 32>::type> 874struct less_than_32_serializer { 875 template <typename BasicJsonType> 876 static void to_json(BasicJsonType& j, T value) { 877 // we want to use ADL, and call the correct to_json overload 878 using nlohmann::to_json; // this method is called by adl_serializer, 879 // this is where the magic happens 880 to_json(j, value); 881 } 882 883 template <typename BasicJsonType> 884 static void from_json(const BasicJsonType& j, T& value) { 885 // same thing here 886 using nlohmann::from_json; 887 from_json(j, value); 888 } 889}; 890``` 891 892Be **very** careful when reimplementing your serializer, you can stack overflow if you don't pay attention: 893 894```cpp 895template <typename T, void> 896struct bad_serializer 897{ 898 template <typename BasicJsonType> 899 static void to_json(BasicJsonType& j, const T& value) { 900 // this calls BasicJsonType::json_serializer<T>::to_json(j, value); 901 // if BasicJsonType::json_serializer == bad_serializer ... oops! 902 j = value; 903 } 904 905 template <typename BasicJsonType> 906 static void to_json(const BasicJsonType& j, T& value) { 907 // this calls BasicJsonType::json_serializer<T>::from_json(j, value); 908 // if BasicJsonType::json_serializer == bad_serializer ... oops! 909 value = j.template get<T>(); // oops! 910 } 911}; 912``` 913 914### Specializing enum conversion 915 916By 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. 917 918It is possible to more precisely specify how a given enum is mapped to and from JSON as shown below: 919 920```cpp 921// example enum type declaration 922enum TaskState { 923 TS_STOPPED, 924 TS_RUNNING, 925 TS_COMPLETED, 926 TS_INVALID=-1, 927}; 928 929// map TaskState values to JSON as strings 930NLOHMANN_JSON_SERIALIZE_ENUM( TaskState, { 931 {TS_INVALID, nullptr}, 932 {TS_STOPPED, "stopped"}, 933 {TS_RUNNING, "running"}, 934 {TS_COMPLETED, "completed"}, 935}) 936``` 937 938The `NLOHMANN_JSON_SERIALIZE_ENUM()` macro declares a set of `to_json()` / `from_json()` functions for type `TaskState` while avoiding repetition and boilerplate serialization code. 939 940**Usage:** 941 942```cpp 943// enum to JSON as string 944json j = TS_STOPPED; 945assert(j == "stopped"); 946 947// json string to enum 948json j3 = "running"; 949assert(j3.get<TaskState>() == TS_RUNNING); 950 951// undefined json value to enum (where the first map entry above is the default) 952json jPi = 3.14; 953assert(jPi.get<TaskState>() == TS_INVALID ); 954``` 955 956Just as in [Arbitrary Type Conversions](#arbitrary-types-conversions) above, 957- `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. 958- It MUST be available (e.g., proper headers must be included) everywhere you use the conversions. 959 960Other Important points: 961- When using `get<ENUM_TYPE>()`, undefined JSON values will default to the first pair specified in your map. Select this default pair carefully. 962- 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. 963 964### Binary formats (BSON, CBOR, MessagePack, and UBJSON) 965 966Though 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), and [UBJSON](https://ubjson.org) (Universal Binary JSON Specification) to efficiently encode JSON values to byte vectors and to decode such vectors. 967 968```cpp 969// create a JSON value 970json j = R"({"compact": true, "schema": 0})"_json; 971 972// serialize to BSON 973std::vector<std::uint8_t> v_bson = json::to_bson(j); 974 975// 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 976 977// roundtrip 978json j_from_bson = json::from_bson(v_bson); 979 980// serialize to CBOR 981std::vector<std::uint8_t> v_cbor = json::to_cbor(j); 982 983// 0xA2, 0x67, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xF5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00 984 985// roundtrip 986json j_from_cbor = json::from_cbor(v_cbor); 987 988// serialize to MessagePack 989std::vector<std::uint8_t> v_msgpack = json::to_msgpack(j); 990 991// 0x82, 0xA7, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xC3, 0xA6, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00 992 993// roundtrip 994json j_from_msgpack = json::from_msgpack(v_msgpack); 995 996// serialize to UBJSON 997std::vector<std::uint8_t> v_ubjson = json::to_ubjson(j); 998 999// 0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D 1000 1001// roundtrip 1002json j_from_ubjson = json::from_ubjson(v_ubjson); 1003``` 1004 1005The 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 of the library. 1006 1007```cpp 1008// CBOR byte string with payload 0xCAFE 1009std::vector<std::uint8_t> v = {0x42, 0xCA, 0xFE}; 1010 1011// read value 1012json j = json::from_cbor(v); 1013 1014// the JSON value has type binary 1015j.is_binary(); // true 1016 1017// get reference to stored binary value 1018auto& binary = j.get_binary(); 1019 1020// the binary value has no subtype (CBOR has no binary subtypes) 1021binary.has_subtype(); // false 1022 1023// access std::vector<std::uint8_t> member functions 1024binary.size(); // 2 1025binary[0]; // 0xCA 1026binary[1]; // 0xFE 1027 1028// set subtype to 0x10 1029binary.set_subtype(0x10); 1030 1031// serialize to MessagePack 1032auto cbor = json::to_msgpack(j); // 0xD5 (fixext2), 0x10, 0xCA, 0xFE 1033``` 1034 1035 1036## Supported compilers 1037 1038Though it's 2021 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work: 1039 1040- GCC 4.8 - 11.0 (and possibly later) 1041- Clang 3.4 - 12.0 (and possibly later) 1042- Apple Clang 9.1 - 12.4 (and possibly later) 1043- Intel C++ Compiler 17.0.2 (and possibly later) 1044- Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later) 1045- Microsoft Visual C++ 2017 / Build Tools 15.5.180.51428 (and possibly later) 1046- Microsoft Visual C++ 2019 / Build Tools 16.3.1+1def00d3d (and possibly later) 1047 1048I would be happy to learn about other compilers/versions. 1049 1050Please note: 1051 1052- 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. 1053- 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. 1054 1055 ``` 1056 APP_STL := c++_shared 1057 NDK_TOOLCHAIN_VERSION := clang3.6 1058 APP_CPPFLAGS += -frtti -fexceptions 1059 ``` 1060 1061 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. 1062 1063- 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). 1064 1065- 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. 1066 1067The following compilers are currently used in continuous integration at [Travis](https://travis-ci.org/nlohmann/json), [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): 1068 1069| Compiler | Operating System | CI Provider | 1070|-------------------------------------------------------------------|--------------------|----------------| 1071| Apple Clang 10.0.1 (clang-1001.0.46.4); Xcode 10.2.1 | macOS 10.14.4 | Travis | 1072| Apple Clang 10.0.1 (clang-1001.0.46.4); Xcode 10.3 | macOS 10.15.7 | GitHub Actions | 1073| Apple Clang 11.0.0 (clang-1100.0.33.12); Xcode 11.2.1 | macOS 10.15.7 | GitHub Actions | 1074| Apple Clang 11.0.0 (clang-1100.0.33.17); Xcode 11.3.1 | macOS 10.15.7 | GitHub Actions | 1075| Apple Clang 11.0.3 (clang-1103.0.32.59); Xcode 11.4.1 | macOS 10.15.7 | GitHub Actions | 1076| Apple Clang 11.0.3 (clang-1103.0.32.62); Xcode 11.5 | macOS 10.15.7 | GitHub Actions | 1077| Apple Clang 11.0.3 (clang-1103.0.32.62); Xcode 11.6 | macOS 10.15.7 | GitHub Actions | 1078| Apple Clang 11.0.3 (clang-1103.0.32.62); Xcode 11.7 | macOS 10.15.7 | GitHub Actions | 1079| Apple Clang 12.0.0 (clang-1200.0.32.2); Xcode 12 | macOS 10.15.7 | GitHub Actions | 1080| Apple Clang 12.0.0 (clang-1200.0.32.21); Xcode 12.1 | macOS 10.15.7 | GitHub Actions | 1081| Apple Clang 12.0.0 (clang-1200.0.32.21); Xcode 12.1.1 | macOS 10.15.7 | GitHub Actions | 1082| Apple Clang 12.0.0 (clang-1200.0.32.27); Xcode 12.2 | macOS 10.15.7 | GitHub Actions | 1083| Apple Clang 12.0.0 (clang-1200.0.32.28); Xcode 12.3 | macOS 10.15.7 | GitHub Actions | 1084| Apple Clang 12.0.0 (clang-1200.0.32.29); Xcode 12.4 | macOS 10.15.7 | GitHub Actions | 1085| GCC 4.8.5 (Ubuntu 4.8.5-4ubuntu2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1086| GCC 4.9.3 (Ubuntu 4.9.3-13ubuntu2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1087| GCC 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.12) | Ubuntu 20.04.2 LTS | GitHub Actions | 1088| GCC 6.5.0 (Ubuntu 6.5.0-2ubuntu1~14.04.1) | Ubuntu 14.04.5 LTS | Travis | 1089| GCC 7.5.0 (Ubuntu 7.5.0-6ubuntu2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1090| GCC 8.1.0 (x86_64-posix-seh-rev0, Built by MinGW-W64 project) | Windows-10.0.17763 | GitHub Actions | 1091| GCC 8.1.0 (i686-posix-dwarf-rev0, Built by MinGW-W64 project) | Windows-10.0.17763 | GitHub Actions | 1092| GCC 8.4.0 (Ubuntu 8.4.0-3ubuntu2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1093| GCC 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) | Ubuntu 20.04.2 LTS | GitHub Actions | 1094| GCC 10.2.0 (Ubuntu 10.2.0-5ubuntu1~20.04) | Ubuntu 20.04.2 LTS | GitHub Actions | 1095| GCC 11.0.1 20210321 (experimental) | Ubuntu 20.04.2 LTS | GitHub Actions | 1096| GCC 11.1.0 | Ubuntu (aarch64) | Drone CI | 1097| Clang 3.5.2 (3.5.2-3ubuntu1) | Ubuntu 20.04.2 LTS | GitHub Actions | 1098| Clang 3.6.2 (3.6.2-3ubuntu2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1099| Clang 3.7.1 (3.7.1-2ubuntu2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1100| Clang 3.8.0 (3.8.0-2ubuntu4) | Ubuntu 20.04.2 LTS | GitHub Actions | 1101| Clang 3.9.1 (3.9.1-4ubuntu3\~16.04.2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1102| Clang 4.0.0 (4.0.0-1ubuntu1\~16.04.2) | Ubuntu 20.04.2 LTS | GitHub Actions | 1103| Clang 5.0.0 (5.0.0-3\~16.04.1) | Ubuntu 20.04.2 LTS | GitHub Actions | 1104| Clang 6.0.1 (6.0.1-14) | Ubuntu 20.04.2 LTS | GitHub Actions | 1105| Clang 7.0.1 (7.0.1-12) | Ubuntu 20.04.2 LTS | GitHub Actions | 1106| Clang 8.0.1 (8.0.1-9) | Ubuntu 20.04.2 LTS | GitHub Actions | 1107| Clang 9.0.1 (9.0.1-12) | Ubuntu 20.04.2 LTS | GitHub Actions | 1108| Clang 10.0.0 (10.0.0-4ubuntu1) | Ubuntu 20.04.2 LTS | GitHub Actions | 1109| Clang 10.0.0 with GNU-like command-line | Windows-10.0.17763 | GitHub Actions | 1110| Clang 11.0.0 with GNU-like command-line | Windows-10.0.17763 | GitHub Actions | 1111| Clang 11.0.0 with MSVC-like command-line | Windows-10.0.17763 | GitHub Actions | 1112| Clang 11.0.0 (11.0.0-2~ubuntu20.04.1) | Ubuntu 20.04.2 LTS | GitHub Actions | 1113| Clang 12.1.0 (12.0.1-++20210423082613+072c90a863aa-1~exp1~20210423063319.76 | Ubuntu 20.04.2 LTS | GitHub Actions | 1114| Visual Studio 14 2015 MSVC 19.0.24241.7 (Build Engine version 14.0.25420.1) | Windows-6.3.9600 | AppVeyor | 1115| Visual Studio 15 2017 MSVC 19.16.27035.0 (Build Engine version 15.9.21+g9802d43bc3 for .NET Framework) | Windows-10.0.14393 | AppVeyor | 1116| Visual Studio 15 2017 MSVC 19.16.27045.0 (Build Engine version 15.9.21+g9802d43bc3 for .NET Framework) | Windows-10.0.14393 | GitHub Actions | 1117| 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 | 1118| Visual Studio 16 2019 MSVC 19.28.29912.0 (Build Engine version 16.9.0+57a23d249 for .NET Framework) | Windows-10.0.17763 | AppVeyor | 1119 1120 1121## Integration 1122 1123[`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 1124 1125```cpp 1126#include <nlohmann/json.hpp> 1127 1128// for convenience 1129using json = nlohmann::json; 1130``` 1131 1132to 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). 1133 1134You 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`. 1135 1136### CMake 1137 1138You 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. 1139 1140#### External 1141 1142To 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: 1143 1144```cmake 1145# CMakeLists.txt 1146find_package(nlohmann_json 3.2.0 REQUIRED) 1147... 1148add_library(foo ...) 1149... 1150target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) 1151``` 1152 1153The package configuration file, `nlohmann_jsonConfig.cmake`, can be used either from an install tree or directly out of the build tree. 1154 1155#### Embedded 1156 1157To 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: 1158 1159```cmake 1160# Typically you don't care so much for a third party library's tests to be 1161# run from your own project's code. 1162set(JSON_BuildTests OFF CACHE INTERNAL "") 1163 1164# If you only include this third party in PRIVATE source files, you do not 1165# need to install it when your main project gets installed. 1166# set(JSON_Install OFF CACHE INTERNAL "") 1167 1168# Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it 1169# unintended consequences that will break the build. It's generally 1170# discouraged (although not necessarily well documented as such) to use 1171# include(...) for pulling in other CMake projects anyways. 1172add_subdirectory(nlohmann_json) 1173... 1174add_library(foo ...) 1175... 1176target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) 1177``` 1178 1179##### Embedded (FetchContent) 1180 1181Since CMake v3.11, 1182[FetchContent](https://cmake.org/cmake/help/v3.11/module/FetchContent.html) can 1183be used to automatically download the repository as a dependency at configure time. 1184 1185Example: 1186```cmake 1187include(FetchContent) 1188 1189FetchContent_Declare(json 1190 GIT_REPOSITORY https://github.com/nlohmann/json.git 1191 GIT_TAG v3.7.3) 1192 1193FetchContent_GetProperties(json) 1194if(NOT json_POPULATED) 1195 FetchContent_Populate(json) 1196 add_subdirectory(${json_SOURCE_DIR} ${json_BINARY_DIR} EXCLUDE_FROM_ALL) 1197endif() 1198 1199target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) 1200``` 1201 1202**Note**: The repository https://github.com/nlohmann/json download size is huge. 1203It contains all the dataset used for the benchmarks. You might want to depend on 1204a smaller repository. For instance, you might want to replace the URL above by 1205https://github.com/ArthurSonzogni/nlohmann_json_cmake_fetchcontent 1206 1207#### Supporting Both 1208 1209To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin to the following: 1210 1211``` cmake 1212# Top level CMakeLists.txt 1213project(FOO) 1214... 1215option(FOO_USE_EXTERNAL_JSON "Use an external JSON library" OFF) 1216... 1217add_subdirectory(thirdparty) 1218... 1219add_library(foo ...) 1220... 1221# Note that the namespaced target will always be available regardless of the 1222# import method 1223target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json) 1224``` 1225```cmake 1226# thirdparty/CMakeLists.txt 1227... 1228if(FOO_USE_EXTERNAL_JSON) 1229 find_package(nlohmann_json 3.2.0 REQUIRED) 1230else() 1231 set(JSON_BuildTests OFF CACHE INTERNAL "") 1232 add_subdirectory(nlohmann_json) 1233endif() 1234... 1235``` 1236 1237`thirdparty/nlohmann_json` is then a complete copy of this source tree. 1238 1239### Package Managers 1240 1241: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. 1242 1243If 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. 1244 1245The 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. 1246 1247If 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. 1248 1249If 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. 1250 1251If 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. 1252 1253If 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). 1254 1255If 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. 1256 1257If 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`). 1258 1259If 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). 1260 1261If 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 files issues [here](https://github.com/hnkb/nlohmann-json-nuget/issues). 1262 1263If 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). 1264 1265If you are using [MSYS2](https://www.msys2.org/), your 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. 1266 1267If 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). 1268Please file issues [here](https://github.com/build2-packaging/nlohmann-json) if you experience problems with the packages. 1269 1270If 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. 1271 1272If 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: 1273 1274```cmake 1275CPMAddPackage( 1276 NAME nlohmann_json 1277 GITHUB_REPOSITORY nlohmann/json 1278 VERSION 3.9.1) 1279``` 1280 1281### Pkg-config 1282 1283If you are using bare Makefiles, you can use `pkg-config` to generate the include flags that point to where the library is installed: 1284 1285```sh 1286pkg-config nlohmann_json --cflags 1287``` 1288 1289Users of the Meson build system will also be able to use a system wide library, which will be found by `pkg-config`: 1290 1291```meson 1292json = dependency('nlohmann_json', required: true) 1293``` 1294 1295 1296## License 1297 1298<img align="right" src="https://opensource.org/trademarks/opensource/OSI-Approved-License-100x137.png"> 1299 1300The class is licensed under the [MIT License](https://opensource.org/licenses/MIT): 1301 1302Copyright © 2013-2021 [Niels Lohmann](https://nlohmann.me) 1303 1304Permission 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: 1305 1306The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. 1307 1308THE 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. 1309 1310* * * 1311 1312The 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> 1313 1314The 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/) 1315 1316The 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/). 1317 1318The 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). 1319 1320## Contact 1321 1322If 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. 1323 1324Only 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). 1325 1326## Security 1327 1328[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). 1329 1330## Thanks 1331 1332I deeply appreciate the help of the following people. 1333 1334<img src="https://raw.githubusercontent.com/nlohmann/json/develop/doc/avatars.png" align="right"> 1335 1336- [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. 1337- [elliotgoodrich](https://github.com/elliotgoodrich) fixed an issue with double deletion in the iterator classes. 1338- [kirkshoop](https://github.com/kirkshoop) made the iterators of the class composable to other libraries. 1339- [wancw](https://github.com/wanwc) fixed a bug that hindered the class to compile with Clang. 1340- Tomas Åblad found a bug in the iterator implementation. 1341- [Joshua C. Randall](https://github.com/jrandall) fixed a bug in the floating-point serialization. 1342- [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. 1343- [Daniel Kopeček](https://github.com/dkopecek) fixed a bug in the compilation with GCC 5.0. 1344- [Florian Weber](https://github.com/Florianjw) fixed a bug in and improved the performance of the comparison operators. 1345- [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. 1346- [易思龙](https://github.com/likebeta) implemented a conversion from anonymous enums. 1347- [kepkin](https://github.com/kepkin) patiently pushed forward the support for Microsoft Visual studio. 1348- [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. 1349- [Caio Luppi](https://github.com/caiovlp) fixed a bug in the Unicode handling. 1350- [dariomt](https://github.com/dariomt) fixed some typos in the examples. 1351- [Daniel Frey](https://github.com/d-frey) cleaned up some pointers and implemented exception-safe memory allocation. 1352- [Colin Hirsch](https://github.com/ColinH) took care of a small namespace issue. 1353- [Huu Nguyen](https://github.com/whoshuu) correct a variable name in the documentation. 1354- [Silverweed](https://github.com/silverweed) overloaded `parse()` to accept an rvalue reference. 1355- [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. 1356- [ZahlGraf](https://github.com/ZahlGraf) added a workaround that allows compilation using Android NDK. 1357- [whackashoe](https://github.com/whackashoe) replaced a function that was marked as unsafe by Visual Studio. 1358- [406345](https://github.com/406345) fixed two small warnings. 1359- [Glen Fernandes](https://github.com/glenfe) noted a potential portability problem in the `has_mapped_type` function. 1360- [Corbin Hughes](https://github.com/nibroc) fixed some typos in the contribution guidelines. 1361- [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. 1362- [Volker Diels-Grabsch](https://github.com/vog) fixed a link in the README file. 1363- [msm-](https://github.com/msm-) added support for American Fuzzy Lop. 1364- [Annihil](https://github.com/Annihil) fixed an example in the README file. 1365- [Themercee](https://github.com/Themercee) noted a wrong URL in the README file. 1366- [Lv Zheng](https://github.com/lv-zheng) fixed a namespace issue with `int64_t` and `uint64_t`. 1367- [abc100m](https://github.com/abc100m) analyzed the issues with GCC 4.8 and proposed a [partial solution](https://github.com/nlohmann/json/pull/212). 1368- [zewt](https://github.com/zewt) added useful notes to the README file about Android. 1369- [Róbert Márki](https://github.com/robertmrk) added a fix to use move iterators and improved the integration via CMake. 1370- [Chris Kitching](https://github.com/ChrisKitching) cleaned up the CMake files. 1371- [Tom Needham](https://github.com/06needhamt) fixed a subtle bug with MSVC 2015 which was also proposed by [Michael K.](https://github.com/Epidal). 1372- [Mário Feroldi](https://github.com/thelostt) fixed a small typo. 1373- [duncanwerner](https://github.com/duncanwerner) found a really embarrassing performance regression in the 2.0.0 release. 1374- [Damien](https://github.com/dtoma) fixed one of the last conversion warnings. 1375- [Thomas Braun](https://github.com/t-b) fixed a warning in a test case and adjusted MSVC calls in the CI. 1376- [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. 1377- [Stefan](https://github.com/5tefan) fixed a minor issue in the documentation. 1378- [Vasil Dimov](https://github.com/vasild) fixed the documentation regarding conversions from `std::multiset`. 1379- [ChristophJud](https://github.com/ChristophJud) overworked the CMake files to ease project inclusion. 1380- [Vladimir Petrigo](https://github.com/vpetrigo) made a SFINAE hack more readable and added Visual Studio 17 to the build matrix. 1381- [Denis Andrejew](https://github.com/seeekr) fixed a grammar issue in the README file. 1382- [Pierre-Antoine Lacaze](https://github.com/palacaze) found a subtle bug in the `dump()` function. 1383- [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. 1384- [cgzones](https://github.com/cgzones) had an idea how to fix the Coverity scan. 1385- [Jared Grubb](https://github.com/jaredgrubb) silenced a nasty documentation warning. 1386- [Yixin Zhang](https://github.com/qwename) fixed an integer overflow check. 1387- [Bosswestfalen](https://github.com/Bosswestfalen) merged two iterator classes into a smaller one. 1388- [Daniel599](https://github.com/Daniel599) helped to get Travis execute the tests with Clang's sanitizers. 1389- [Jonathan Lee](https://github.com/vjon) fixed an example in the README file. 1390- [gnzlbg](https://github.com/gnzlbg) supported the implementation of user-defined types. 1391- [Alexej Harm](https://github.com/qis) helped to get the user-defined types working with Visual Studio. 1392- [Jared Grubb](https://github.com/jaredgrubb) supported the implementation of user-defined types. 1393- [EnricoBilla](https://github.com/EnricoBilla) noted a typo in an example. 1394- [Martin Hořeňovský](https://github.com/horenmar) found a way for a 2x speedup for the compilation time of the test suite. 1395- [ukhegg](https://github.com/ukhegg) found proposed an improvement for the examples section. 1396- [rswanson-ihi](https://github.com/rswanson-ihi) noted a typo in the README. 1397- [Mihai Stan](https://github.com/stanmihai4) fixed a bug in the comparison with `nullptr`s. 1398- [Tushar Maheshwari](https://github.com/tusharpm) added [cotire](https://github.com/sakra/cotire) support to speed up the compilation. 1399- [TedLyngmo](https://github.com/TedLyngmo) noted a typo in the README, removed unnecessary bit arithmetic, and fixed some `-Weffc++` warnings. 1400- [Krzysztof Woś](https://github.com/krzysztofwos) made exceptions more visible. 1401- [ftillier](https://github.com/ftillier) fixed a compiler warning. 1402- [tinloaf](https://github.com/tinloaf) made sure all pushed warnings are properly popped. 1403- [Fytch](https://github.com/Fytch) found a bug in the documentation. 1404- [Jay Sistar](https://github.com/Type1J) implemented a Meson build description. 1405- [Henry Lee](https://github.com/HenryRLee) fixed a warning in ICC and improved the iterator implementation. 1406- [Vincent Thiery](https://github.com/vthiery) maintains a package for the Conan package manager. 1407- [Steffen](https://github.com/koemeet) fixed a potential issue with MSVC and `std::min`. 1408- [Mike Tzou](https://github.com/Chocobo1) fixed some typos. 1409- [amrcode](https://github.com/amrcode) noted a misleading documentation about comparison of floats. 1410- [Oleg Endo](https://github.com/olegendo) reduced the memory consumption by replacing `<iostream>` with `<iosfwd>`. 1411- [dan-42](https://github.com/dan-42) cleaned up the CMake files to simplify including/reusing of the library. 1412- [Nikita Ofitserov](https://github.com/himikof) allowed for moving values from initializer lists. 1413- [Greg Hurrell](https://github.com/wincent) fixed a typo. 1414- [Dmitry Kukovinets](https://github.com/DmitryKuk) fixed a typo. 1415- [kbthomp1](https://github.com/kbthomp1) fixed an issue related to the Intel OSX compiler. 1416- [Markus Werle](https://github.com/daixtrose) fixed a typo. 1417- [WebProdPP](https://github.com/WebProdPP) fixed a subtle error in a precondition check. 1418- [Alex](https://github.com/leha-bot) noted an error in a code sample. 1419- [Tom de Geus](https://github.com/tdegeus) reported some warnings with ICC and helped fixing them. 1420- [Perry Kundert](https://github.com/pjkundert) simplified reading from input streams. 1421- [Sonu Lohani](https://github.com/sonulohani) fixed a small compilation error. 1422- [Jamie Seward](https://github.com/jseward) fixed all MSVC warnings. 1423- [Nate Vargas](https://github.com/eld00d) added a Doxygen tag file. 1424- [pvleuven](https://github.com/pvleuven) helped fixing a warning in ICC. 1425- [Pavel](https://github.com/crea7or) helped fixing some warnings in MSVC. 1426- [Jamie Seward](https://github.com/jseward) avoided unnecessary string copies in `find()` and `count()`. 1427- [Mitja](https://github.com/Itja) fixed some typos. 1428- [Jorrit Wronski](https://github.com/jowr) updated the Hunter package links. 1429- [Matthias Möller](https://github.com/TinyTinni) added a `.natvis` for the MSVC debug view. 1430- [bogemic](https://github.com/bogemic) fixed some C++17 deprecation warnings. 1431- [Eren Okka](https://github.com/erengy) fixed some MSVC warnings. 1432- [abolz](https://github.com/abolz) integrated the Grisu2 algorithm for proper floating-point formatting, allowing more roundtrip checks to succeed. 1433- [Vadim Evard](https://github.com/Pipeliner) fixed a Markdown issue in the README. 1434- [zerodefect](https://github.com/zerodefect) fixed a compiler warning. 1435- [Kert](https://github.com/kaidokert) allowed to template the string type in the serialization and added the possibility to override the exceptional behavior. 1436- [mark-99](https://github.com/mark-99) helped fixing an ICC error. 1437- [Patrik Huber](https://github.com/patrikhuber) fixed links in the README file. 1438- [johnfb](https://github.com/johnfb) found a bug in the implementation of CBOR's indefinite length strings. 1439- [Paul Fultz II](https://github.com/pfultz2) added a note on the cget package manager. 1440- [Wilson Lin](https://github.com/wla80) made the integration section of the README more concise. 1441- [RalfBielig](https://github.com/ralfbielig) detected and fixed a memory leak in the parser callback. 1442- [agrianius](https://github.com/agrianius) allowed to dump JSON to an alternative string type. 1443- [Kevin Tonon](https://github.com/ktonon) overworked the C++11 compiler checks in CMake. 1444- [Axel Huebl](https://github.com/ax3l) simplified a CMake check and added support for the [Spack package manager](https://spack.io). 1445- [Carlos O'Ryan](https://github.com/coryan) fixed a typo. 1446- [James Upjohn](https://github.com/jammehcow) fixed a version number in the compilers section. 1447- [Chuck Atkins](https://github.com/chuckatkins) adjusted the CMake files to the CMake packaging guidelines and provided documentation for the CMake integration. 1448- [Jan Schöppach](https://github.com/dns13) fixed a typo. 1449- [martin-mfg](https://github.com/martin-mfg) fixed a typo. 1450- [Matthias Möller](https://github.com/TinyTinni) removed the dependency from `std::stringstream`. 1451- [agrianius](https://github.com/agrianius) added code to use alternative string implementations. 1452- [Daniel599](https://github.com/Daniel599) allowed to use more algorithms with the `items()` function. 1453- [Julius Rakow](https://github.com/jrakow) fixed the Meson include directory and fixed the links to [cppreference.com](cppreference.com). 1454- [Sonu Lohani](https://github.com/sonulohani) fixed the compilation with MSVC 2015 in debug mode. 1455- [grembo](https://github.com/grembo) fixed the test suite and re-enabled several test cases. 1456- [Hyeon Kim](https://github.com/simnalamburt) introduced the macro `JSON_INTERNAL_CATCH` to control the exception handling inside the library. 1457- [thyu](https://github.com/thyu) fixed a compiler warning. 1458- [David Guthrie](https://github.com/LEgregius) fixed a subtle compilation error with Clang 3.4.2. 1459- [Dennis Fischer](https://github.com/dennisfischer) allowed to call `find_package` without installing the library. 1460- [Hyeon Kim](https://github.com/simnalamburt) fixed an issue with a double macro definition. 1461- [Ben Berman](https://github.com/rivertam) made some error messages more understandable. 1462- [zakalibit](https://github.com/zakalibit) fixed a compilation problem with the Intel C++ compiler. 1463- [mandreyel](https://github.com/mandreyel) fixed a compilation problem. 1464- [Kostiantyn Ponomarenko](https://github.com/koponomarenko) added version and license information to the Meson build file. 1465- [Henry Schreiner](https://github.com/henryiii) added support for GCC 4.8. 1466- [knilch](https://github.com/knilch0r) made sure the test suite does not stall when run in the wrong directory. 1467- [Antonio Borondo](https://github.com/antonioborondo) fixed an MSVC 2017 warning. 1468- [Dan Gendreau](https://github.com/dgendreau) implemented the `NLOHMANN_JSON_SERIALIZE_ENUM` macro to quickly define a enum/JSON mapping. 1469- [efp](https://github.com/efp) added line and column information to parse errors. 1470- [julian-becker](https://github.com/julian-becker) added BSON support. 1471- [Pratik Chowdhury](https://github.com/pratikpc) added support for structured bindings. 1472- [David Avedissian](https://github.com/davedissian) added support for Clang 5.0.1 (PS4 version). 1473- [Jonathan Dumaresq](https://github.com/dumarjo) implemented an input adapter to read from `FILE*`. 1474- [kjpus](https://github.com/kjpus) fixed a link in the documentation. 1475- [Manvendra Singh](https://github.com/manu-chroma) fixed a typo in the documentation. 1476- [ziggurat29](https://github.com/ziggurat29) fixed an MSVC warning. 1477- [Sylvain Corlay](https://github.com/SylvainCorlay) added code to avoid an issue with MSVC. 1478- [mefyl](https://github.com/mefyl) fixed a bug when JSON was parsed from an input stream. 1479- [Millian Poquet](https://github.com/mpoquet) allowed to install the library via Meson. 1480- [Michael Behrns-Miller](https://github.com/moodboom) found an issue with a missing namespace. 1481- [Nasztanovics Ferenc](https://github.com/naszta) fixed a compilation issue with libc 2.12. 1482- [Andreas Schwab](https://github.com/andreas-schwab) fixed the endian conversion. 1483- [Mark-Dunning](https://github.com/Mark-Dunning) fixed a warning in MSVC. 1484- [Gareth Sylvester-Bradley](https://github.com/garethsb-sony) added `operator/` for JSON Pointers. 1485- [John-Mark](https://github.com/johnmarkwayve) noted a missing header. 1486- [Vitaly Zaitsev](https://github.com/xvitaly) fixed compilation with GCC 9.0. 1487- [Laurent Stacul](https://github.com/stac47) fixed compilation with GCC 9.0. 1488- [Ivor Wanders](https://github.com/iwanders) helped reducing the CMake requirement to version 3.1. 1489- [njlr](https://github.com/njlr) updated the Buckaroo instructions. 1490- [Lion](https://github.com/lieff) fixed a compilation issue with GCC 7 on CentOS. 1491- [Isaac Nickaein](https://github.com/nickaein) improved the integer serialization performance and implemented the `contains()` function. 1492- [past-due](https://github.com/past-due) suppressed an unfixable warning. 1493- [Elvis Oric](https://github.com/elvisoric) improved Meson support. 1494- [Matěj Plch](https://github.com/Afforix) fixed an example in the README. 1495- [Mark Beckwith](https://github.com/wythe) fixed a typo. 1496- [scinart](https://github.com/scinart) fixed bug in the serializer. 1497- [Patrick Boettcher](https://github.com/pboettch) implemented `push_back()` and `pop_back()` for JSON Pointers. 1498- [Bruno Oliveira](https://github.com/nicoddemus) added support for Conda. 1499- [Michele Caini](https://github.com/skypjack) fixed links in the README. 1500- [Hani](https://github.com/hnkb) documented how to install the library with NuGet. 1501- [Mark Beckwith](https://github.com/wythe) fixed a typo. 1502- [yann-morin-1998](https://github.com/yann-morin-1998) helped reducing the CMake requirement to version 3.1. 1503- [Konstantin Podsvirov](https://github.com/podsvirov) maintains a package for the MSYS2 software distro. 1504- [remyabel](https://github.com/remyabel) added GNUInstallDirs to the CMake files. 1505- [Taylor Howard](https://github.com/taylorhoward92) fixed a unit test. 1506- [Gabe Ron](https://github.com/Macr0Nerd) implemented the `to_string` method. 1507- [Watal M. Iwasaki](https://github.com/heavywatal) fixed a Clang warning. 1508- [Viktor Kirilov](https://github.com/onqtam) switched the unit tests from [Catch](https://github.com/philsquared/Catch) to [doctest](https://github.com/onqtam/doctest) 1509- [Juncheng E](https://github.com/ejcjason) fixed a typo. 1510- [tete17](https://github.com/tete17) fixed a bug in the `contains` function. 1511- [Xav83](https://github.com/Xav83) fixed some cppcheck warnings. 1512- [0xflotus](https://github.com/0xflotus) fixed some typos. 1513- [Christian Deneke](https://github.com/chris0x44) added a const version of `json_pointer::back`. 1514- [Julien Hamaide](https://github.com/crazyjul) made the `items()` function work with custom string types. 1515- [Evan Nemerson](https://github.com/nemequ) updated fixed a bug in Hedley and updated this library accordingly. 1516- [Florian Pigorsch](https://github.com/flopp) fixed a lot of typos. 1517- [Camille Bégué](https://github.com/cbegue) fixed an issue in the conversion from `std::pair` and `std::tuple` to `json`. 1518- [Anthony VH](https://github.com/AnthonyVH) fixed a compile error in an enum deserialization. 1519- [Yuriy Vountesmery](https://github.com/ua-code-dragon) noted a subtle bug in a preprocessor check. 1520- [Chen](https://github.com/dota17) fixed numerous issues in the library. 1521- [Antony Kellermann](https://github.com/aokellermann) added a CI step for GCC 10.1. 1522- [Alex](https://github.com/gistrec) fixed an MSVC warning. 1523- [Rainer](https://github.com/rvjr) proposed an improvement in the floating-point serialization in CBOR. 1524- [Francois Chabot](https://github.com/FrancoisChabot) made performance improvements in the input adapters. 1525- [Arthur Sonzogni](https://github.com/ArthurSonzogni) documented how the library can be included via `FetchContent`. 1526- [Rimas Misevičius](https://github.com/rmisev) fixed an error message. 1527- [Alexander Myasnikov](https://github.com/alexandermyasnikov) fixed some examples and a link in the README. 1528- [Hubert Chathi](https://github.com/uhoreg) made CMake's version config file architecture-independent. 1529- [OmnipotentEntity](https://github.com/OmnipotentEntity) implemented the binary values for CBOR, MessagePack, BSON, and UBJSON. 1530- [ArtemSarmini](https://github.com/ArtemSarmini) fixed a compilation issue with GCC 10 and fixed a leak. 1531- [Evgenii Sopov](https://github.com/sea-kg) integrated the library to the wsjcpp package manager. 1532- [Sergey Linev](https://github.com/linev) fixed a compiler warning. 1533- [Miguel Magalhães](https://github.com/magamig) fixed the year in the copyright. 1534- [Gareth Sylvester-Bradley](https://github.com/garethsb-sony) fixed a compilation issue with MSVC. 1535- [Alexander “weej” Jones](https://github.com/alex-weej) fixed an example in the README. 1536- [Antoine Cœur](https://github.com/Coeur) fixed some typos in the documentation. 1537- [jothepro](https://github.com/jothepro) updated links to the Hunter package. 1538- [Dave Lee](https://github.com/kastiglione) fixed link in the README. 1539- [Joël Lamotte](https://github.com/Klaim) added instruction for using Build2's package manager. 1540- [Paul Jurczak](https://github.com/pauljurczak) fixed an example in the README. 1541- [Sonu Lohani](https://github.com/sonulohani) fixed a warning. 1542- [Carlos Gomes Martinho](https://github.com/gocarlos) updated the Conan package source. 1543- [Konstantin Podsvirov](https://github.com/podsvirov) fixed the MSYS2 package documentation. 1544- [Tridacnid](https://github.com/Tridacnid) improved the CMake tests. 1545- [Michael](https://github.com/MBalszun) fixed MSVC warnings. 1546- [Quentin Barbarat](https://github.com/quentin-dev) fixed an example in the documentation. 1547- [XyFreak](https://github.com/XyFreak) fixed a compiler warning. 1548- [TotalCaesar659](https://github.com/TotalCaesar659) fixed links in the README. 1549- [Tanuj Garg](https://github.com/tanuj208) improved the fuzzer coverage for UBSAN input. 1550- [AODQ](https://github.com/AODQ) fixed a compiler warning. 1551- [jwittbrodt](https://github.com/jwittbrodt) made `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` inline. 1552- [pfeatherstone](https://github.com/pfeatherstone) improved the upper bound of arguments of the `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`/`NLOHMANN_DEFINE_TYPE_INTRUSIVE` macros. 1553- [Jan Procházka](https://github.com/jprochazk) fixed a bug in the CBOR parser for binary and string values. 1554- [T0b1-iOS](https://github.com/T0b1-iOS) fixed a bug in the new hash implementation. 1555- [Matthew Bauer](https://github.com/matthewbauer) adjusted the CBOR writer to create tags for binary subtypes. 1556- [gatopeich](https://github.com/gatopeich) implemented an ordered map container for `nlohmann::ordered_json`. 1557- [Érico Nogueira Rolim](https://github.com/ericonr) added support for pkg-config. 1558- [KonanM](https://github.com/KonanM) proposed an implementation for the `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`/`NLOHMANN_DEFINE_TYPE_INTRUSIVE` macros. 1559- [Guillaume Racicot](https://github.com/gracicot) implemented `string_view` support and allowed C++20 support. 1560- [Alex Reinking](https://github.com/alexreinking) improved CMake support for `FetchContent`. 1561- [Hannes Domani](https://github.com/ssbssa) provided a GDB pretty printer. 1562- Lars Wirzenius reviewed the README file. 1563- [Jun Jie](https://github.com/ongjunjie) fixed a compiler path in the CMake scripts. 1564- [Ronak Buch](https://github.com/rbuch) fixed typos in the documentation. 1565- [Alexander Karzhenkov](https://github.com/karzhenkov) fixed a move constructor and the Travis builds. 1566- [Leonardo Lima](https://github.com/leozz37) added CPM.Cmake support. 1567- [Joseph Blackman](https://github.com/jbzdarkid) fixed a warning. 1568- [Yaroslav](https://github.com/YarikTH) updated doctest and implemented unit tests. 1569- [Martin Stump](https://github.com/globberwops) fixed a bug in the CMake files. 1570- [Jaakko Moisio](https://github.com/jasujm) fixed a bug in the input adapters. 1571- [bl-ue](https://github.com/bl-ue) fixed some Markdown issues in the README file. 1572- [William A. Wieselquist](https://github.com/wawiesel) fixed an example from the README. 1573- [abbaswasim](https://github.com/abbaswasim) fixed an example from the README. 1574- [Remy Jette](https://github.com/remyjette) fixed a warning. 1575- [Fraser](https://github.com/frasermarlow) fixed the documentation. 1576- [Ben Beasley](https://github.com/musicinmybrain) updated doctest. 1577- [Doron Behar](https://github.com/doronbehar) fixed pkg-config.pc. 1578- [raduteo](https://github.com/raduteo) fixed a warning. 1579- [David Pfahler](https://github.com/theShmoo) added the possibility to compile the library without I/O support. 1580- [Morten Fyhn Amundsen](https://github.com/mortenfyhn) fixed a typo. 1581- [jpl-mac](https://github.com/jpl-mac) allowed to treat the library as a system header in CMake. 1582- [Jason Dsouza](https://github.com/jasmcaus) fixed the indentation of the CMake file. 1583- [offa](https://github.com/offa) added a link to Conan Center to the documentation. 1584- [TotalCaesar659](https://github.com/TotalCaesar659) updated the links in the documentation to use HTTPS. 1585- [Rafail Giavrimis](https://github.com/grafail) fixed the Google Benchmark default branch. 1586- [Louis Dionne](https://github.com/ldionne) fixed a conversion operator. 1587- [justanotheranonymoususer](https://github.com/justanotheranonymoususer) made the examples in the README more consistent. 1588- [Finkman](https://github.com/Finkman) suppressed some `-Wfloat-equal` warnings. 1589- [Ferry Huberts](https://github.com/fhuberts) fixed `-Wswitch-enum` warnings. 1590 1591Thanks a lot for helping out! Please [let me know](mailto:mail@nlohmann.me) if I forgot someone. 1592 1593 1594## Used third-party tools 1595 1596The 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! 1597 1598- [**amalgamate.py - Amalgamate C source and header files**](https://github.com/edlund/amalgamate) to create a single header file 1599- [**American fuzzy lop**](https://lcamtuf.coredump.cx/afl/) for fuzz testing 1600- [**AppVeyor**](https://www.appveyor.com) for [continuous integration](https://ci.appveyor.com/project/nlohmann/json) on Windows 1601- [**Artistic Style**](http://astyle.sourceforge.net) for automatic source code indentation 1602- [**Clang**](https://clang.llvm.org) for compilation with code sanitizers 1603- [**CMake**](https://cmake.org) for build automation 1604- [**Codacity**](https://www.codacy.com) for further [code analysis](https://www.codacy.com/app/nlohmann/json) 1605- [**Coveralls**](https://coveralls.io) to measure [code coverage](https://coveralls.io/github/nlohmann/json) 1606- [**Coverity Scan**](https://scan.coverity.com) for [static analysis](https://scan.coverity.com/projects/nlohmann-json) 1607- [**cppcheck**](http://cppcheck.sourceforge.net) for static analysis 1608- [**doctest**](https://github.com/onqtam/doctest) for the unit tests 1609- [**Doxygen**](https://www.doxygen.nl/index.html) to generate [documentation](https://nlohmann.github.io/json/doxygen/index.html) 1610- [**git-update-ghpages**](https://github.com/rstacruz/git-update-ghpages) to upload the documentation to gh-pages 1611- [**GitHub Changelog Generator**](https://github.com/skywinder/github-changelog-generator) to generate the [ChangeLog](https://github.com/nlohmann/json/blob/develop/ChangeLog.md) 1612- [**Google Benchmark**](https://github.com/google/benchmark) to implement the benchmarks 1613- [**Hedley**](https://nemequ.github.io/hedley/) to avoid re-inventing several compiler-agnostic feature macros 1614- [**lcov**](http://ltp.sourceforge.net/coverage/lcov.php) to process coverage information and create a HTML view 1615- [**libFuzzer**](https://llvm.org/docs/LibFuzzer.html) to implement fuzz testing for OSS-Fuzz 1616- [**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)) 1617- [**Probot**](https://probot.github.io) for automating maintainer tasks such as closing stale issues, requesting missing information, or detecting toxic comments. 1618- [**send_to_wandbox**](https://github.com/nlohmann/json/blob/develop/doc/scripts/send_to_wandbox.py) to send code examples to [Wandbox](https://wandbox.org) 1619- [**Travis**](https://travis-ci.org) for [continuous integration](https://travis-ci.org/nlohmann/json) on Linux and macOS 1620- [**Valgrind**](https://valgrind.org) to check for correct memory management 1621- [**Wandbox**](https://wandbox.org) for [online examples](https://wandbox.org/permlink/3lCHrFUZANONKv7a) 1622 1623 1624## Projects using JSON for Modern C++ 1625 1626The library is currently used in Apple macOS Sierra and iOS 10. I am not sure what they are using the library for, but I am happy that it runs on so many devices. 1627 1628 1629## Notes 1630 1631### Character encoding 1632 1633The library supports **Unicode input** as follows: 1634 1635- 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). 1636- `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. 1637- Other encodings such as Latin-1 or ISO 8859-1 are **not** supported and will yield parse or serialization errors. 1638- [Unicode noncharacters](https://www.unicode.org/faq/private_use.html#nonchar1) will not be replaced by the library. 1639- Invalid surrogates (e.g., incomplete pairs such as `\uDEAD`) will yield parse errors. 1640- 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. 1641- When you store strings with different encodings in the library, calling [`dump()`](https://nlohmann.github.io/json/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. 1642- To store wide strings (e.g., `std::wstring`), you need to convert them to a a UTF-8 encoded `std::string` before, see [an example](https://json.nlohmann.me/home/faq/#wide-string-handling). 1643 1644### Comments in JSON 1645 1646This library does not support comments by default. It does so for three reasons: 1647 16481. 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. 16492. This was not an oversight: Douglas Crockford [wrote on this](https://plus.google.com/118095276221607585885/posts/RK8qyGVaGSr) in May 2012: 1650 1651 > 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. 1652 1653 > 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. 1654 16553. 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. 1656 1657However, you can pass set parameter `ignore_comments` to true in the `parse` function to ignore `//` or `/* */` comments. Comments will then be treated as whitespace. 1658 1659### Order of object keys 1660 1661By 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". 1662 1663If 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)). 1664 1665### Memory Release 1666 1667We checked with Valgrind and the Address Sanitizer (ASAN) that there are no memory leaks. 1668 1669If you find that a parsing program with this library does not release memory, please consider the following case and it maybe unrelated to this library. 1670 1671**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. 1672Here is a related issue [#1924](https://github.com/nlohmann/json/issues/1924). 1673 1674### Further notes 1675 1676- 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://nlohmann.github.io/json/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://nlohmann.github.io/json/api/basic_json/at/). Furthermore, you can define `JSON_ASSERT(x)` to replace calls to `assert(x)`. 1677- As the exact type of a number 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. 1678- The code can be compiled without C++ **runtime type identification** features; that is, you can use the `-fno-rtti` compiler flag. 1679- **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). 1680 1681## Execute unit tests 1682 1683To compile and run the tests, you need to execute 1684 1685```sh 1686$ mkdir build 1687$ cd build 1688$ cmake .. -DJSON_BuildTests=On 1689$ cmake --build . 1690$ ctest --output-on-failure 1691``` 1692 1693Note 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. 1694 1695In 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. 1696 1697Some 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. 1698 1699Note 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. 1700 1701As 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. 1702
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
