1# <small>nlohmann::basic_json::</small>accept 2 3```cpp 4// (1) 5template<typename InputType> 6static bool accept(InputType&& i, 7 const bool ignore_comments = false); 8 9// (2) 10template<typename IteratorType> 11static bool accept(IteratorType first, IteratorType last, 12 const bool ignore_comments = false); 13``` 14 15Checks whether the input is valid JSON. 16 171. Reads from a compatible input. 182. Reads from a pair of character iterators 19 20 The value_type of the iterator must be an integral type with size of 1, 2 or 4 bytes, which will be interpreted 21 respectively as UTF-8, UTF-16 and UTF-32. 22 23Unlike the [`parse`](parse.md) function, this function neither throws an exception in case of invalid JSON input 24(i.e., a parse error) nor creates diagnostic information. 25 26## Template parameters 27 28`InputType` 29: A compatible input, for instance: 30 31 - an `std::istream` object 32 - a `FILE` pointer (must not be null) 33 - a C-style array of characters 34 - a pointer to a null-terminated string of single byte characters 35 - a `std::string` 36 - an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators. 37 38`IteratorType` 39: a compatible iterator type, for instance. 40 41 - a pair of `std::string::iterator` or `std::vector<std::uint8_t>::iterator` 42 - a pair of pointers such as `ptr` and `ptr + len` 43 44## Parameters 45 46`i` (in) 47: Input to parse from. 48 49`ignore_comments` (in) 50: whether comments should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error 51 (`#!cpp false`); (optional, `#!cpp false` by default) 52 53`first` (in) 54: iterator to start of character range 55 56`last` (in) 57: iterator to end of character range 58 59## Return value 60 61Whether the input is valid JSON. 62 63## Exception safety 64 65Strong guarantee: if an exception is thrown, there are no changes in the JSON value. 66 67## Complexity 68 69Linear in the length of the input. The parser is a predictive LL(1) parser. 70 71## Notes 72 73(1) A UTF-8 byte order mark is silently ignored. 74 75!!! danger "Runtime assertion" 76 77 The precondition that a passed `#!cpp FILE` pointer must not be null is enforced with a 78 [runtime assertion](../../features/assertions.md). 79 80## Examples 81 82??? example 83 84 The example below demonstrates the `accept()` function reading from a string. 85 86 ```cpp 87 --8<-- "examples/accept__string.cpp" 88 ``` 89 90 Output: 91 92 ```json 93 --8<-- "examples/accept__string.output" 94 ``` 95 96## See also 97 98- [parse](parse.md) - deserialize from a compatible input 99- [operator>>](../operator_gtgt.md) - deserialize from stream 100 101## Version history 102 103- Added in version 3.0.0. 104- Ignoring comments via `ignore_comments` added in version 3.9.0. 105 106!!! warning "Deprecation" 107 108 Overload (2) replaces calls to `accept` with a pair of iterators as their first parameter which has been 109 deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like 110 `#!cpp accept({ptr, ptr+len}, ...);` with `#!cpp accept(ptr, ptr+len, ...);`. 111 112 You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated 113 function. 114