api/basic_json_document/accept.md

# <small>nlohmann::basic_json_document::</small>accept

```cpp
template<typename InputType>
static bool accept(InputType&& input,
                   const bool ignore_comments = false,
                   const bool ignore_trailing_commas = false);
```

Checks whether the input is valid JSON, accepting and rejecting exactly what
[`BasicJsonType::accept()`](../basic_json/accept.md) does, with the same options. Unlike [`parse()`](parse.md), this
function never throws an exception for invalid input, and the returned `#!cpp bool` is the only result -- no document
is returned.

The result is the same as that of `BasicJsonType::accept()` by design; the difference is how the check is made. This
function runs the document's index builder (and discards the index), while `BasicJsonType::accept()` runs the SAX
parser with a handler that ignores every event. Use this one if you go on to parse the same input with
[`parse()`](parse.md) anyway, so that both use the same code; either is fine for a plain yes/no answer.

## Template parameters

`InputType`
:   A compatible input; see [`parse`](parse.md#template-parameters).

## Parameters

`input` (in)
:   Input to check.

`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)

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

## Return value

Whether the input is valid JSON.

## Exception safety

Strong guarantee: this function itself never throws for an invalid input; it can only throw what allocating the
input's own copy (for inputs that are always read into a buffer) throws.

## Complexity

Linear in the length of the input.

## Notes

An integer argument that is not a `#!cpp bool` where the flags are expected, such as `#!cpp accept(ptr, len)`, does not
compile; see [`parse`](parse.md#notes).

## Examples

??? example

    ```cpp
    #include <iostream>
    #include <nlohmann/json.hpp>
    #include <nlohmann/json_view.hpp>
    
    using json_document = nlohmann::json_document;
    
    int main()
    {
        std::cout << std::boolalpha;
    
        // accept() behaves exactly like basic_json::accept(): the same inputs are
        // accepted or rejected, with the same ignore_comments/ignore_trailing_commas
        // options
        std::cout << json_document::accept(R"({"a": 1})") << '\n';
        std::cout << json_document::accept(R"({"a": 1,})") << '\n'; // trailing comma: rejected by default
        std::cout << json_document::accept(R"({"a": 1,})", false, true) << '\n'; // ignore_trailing_commas
    
        std::cout << (json_document::accept(R"({"a": 1})") == nlohmann::json::accept(R"({"a": 1})")) << '\n';
    }
    
    ```

    Output:

    ```json
    true
    false
    true
    true
    
    ```

## See also

- [parse](parse.md) - deserialize from a compatible input
- [`BasicJsonType::accept`](../basic_json/accept.md) - the corresponding function of `basic_json`

## Version history

- Added in version 3.13.0.