1# basic_json::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 a 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 33 - a C-style array of characters 34 - a pointer to a null-terminated string of single byte characters 35 - an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators. 36 37`IteratorType` 38: a compatible iterator type 39 40## Parameters 41 42`i` (in) 43: Input to parse from. 44 45`ignore_comments` (in) 46: whether comments should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error 47 (`#!cpp false`); (optional, `#!cpp false` by default) 48 49`first` (in) 50: iterator to start of character range 51 52`last` (in) 53: iterator to end of character range 54 55## Return value 56 57Whether the input is valid JSON. 58 59## Exception safety 60 61Strong guarantee: if an exception is thrown, there are no changes in the JSON value. 62 63## Complexity 64 65Linear in the length of the input. The parser is a predictive LL(1) parser. 66 67## Notes 68 69(1) A UTF-8 byte order mark is silently ignored. 70 71## Examples 72 73??? example 74 75 The example below demonstrates the `accept()` function reading from a string. 76 77 ```cpp 78 --8<-- "examples/accept__string.cpp" 79 ``` 80 81 Output: 82 83 ```json 84 --8<-- "examples/accept__string.output" 85 ``` 86 87## Version history 88 89- Added in version 3.0.0. 90- Ignoring comments via `ignore_comments` added in version 3.9.0. 91