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nlohmann::basic_json_document::accept

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() does, with the same options. Unlike parse(), this function never throws an exception for invalid input, and the returned 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() 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.

Parameters

input (in)
Input to check.
ignore_comments (in)
whether comments should be ignored and treated like whitespace (true) or yield a parse error (false); (optional, false by default)
ignore_trailing_commas (in)
whether trailing commas in arrays or objects should be ignored and treated like whitespace (true) or yield a parse error (false); (optional, 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 bool where the flags are expected, such as accept(ptr, len), does not compile; see parse.

Examples

Example 
#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:

true
false
true
true

See also

Version history

  • Added in version 3.13.0 unreleased.