json/doc/mkdocs/docs/api/basic_json/accept.md

# basic_json::accept

```cpp
// (1)
template<typename InputType>
static bool accept(InputType&& i,
                   const bool ignore_comments = false);

// (2)
template<typename IteratorType>
static bool accept(IteratorType first, IteratorType last,
                   const bool ignore_comments = false);
```

Checks whether the input is valid JSON.

1. Reads from a compatible input.
2. Reads from a pair of character iterators
    
    The value_type of the iterator must be a integral type with size of 1, 2 or 4 bytes, which will be interpreted
    respectively as UTF-8, UTF-16 and UTF-32.
    
Unlike the [`parse`](parse.md) function, this function neither throws an exception in case of invalid JSON input
(i.e., a parse error) nor creates diagnostic information.

## Template parameters

`InputType`
:   A compatible input, for instance:
    
    - an `std::istream` object
    - a `FILE` pointer
    - a C-style array of characters
    - a pointer to a null-terminated string of single byte characters
    - an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators.

`IteratorType`
:   a compatible iterator type

## Parameters

`i` (in)
:   Input to parse from.

`ignore_comments` (in)
:   whether comments should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error
    (`#!cpp false`); (optional, `#!cpp false` by default)

`first` (in)
:   iterator to start of character range

`last` (in)
:   iterator to end of character range

## Return value

Whether the input is valid JSON.

## Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

## Complexity

Linear in the length of the input. The parser is a predictive LL(1) parser.

## Notes

(1) A UTF-8 byte order mark is silently ignored.

## Examples

??? example

    The example below demonstrates the `accept()` function reading from a string.

    ```cpp
    --8<-- "examples/accept__string.cpp"
    ```
    
    Output:
    
    ```json
    --8<-- "examples/accept__string.output"
    ```

## Version history

- Added in version 3.0.0.
- Ignoring comments via `ignore_comments` added in version 3.9.0.