nlohmann::basic_json_document::parse_copy¶

template<typename InputType>
static basic_json_document parse_copy(InputType&& input,
                                      const bool allow_exceptions = true,
                                      const bool ignore_comments = false,
                                      const bool ignore_trailing_commas = false);

Deserialize from a compatible input, always taking the document's own copy of it, regardless of the value category or type of input. Unlike parse(), the returned document never depends on input staying alive.

Template parameters¶

InputType: A compatible input; see parse.

Parameters¶

input (in): Input to parse from.
allow_exceptions (in): whether to throw exceptions in case of a parse error (optional, true by default)
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¶

The parsed document, with owns_source() true. If allow_exceptions is false and the input is not valid JSON, the returned document is discarded; see is_discarded.

Exceptions¶

Same as parse.

Complexity¶

Linear in the length of the input.

Notes¶

parse_copy() accepts and rejects exactly what parse() does, and classifies numbers the same way; it only differs in that the input is always copied rather than sometimes borrowed. Prefer parse() when the input's lifetime already covers the document's, since it avoids the copy for borrowed inputs.

An integer argument that is not a bool where the flags are expected, such as parse_copy(ptr, len), does not compile; see parse.

Examples¶

Example

The example below returns a document from a function whose local buffer would otherwise not outlive it.

#include <iostream>
#include <nlohmann/json_view.hpp>

using json_document = nlohmann::json_document;

json_document parse_from_temporary_buffer()
{
    char buffer[] = R"({"a": 1})";
    // parse() would borrow `buffer`, which is about to go out of scope;
    // parse_copy() takes its own copy instead, so the returned document does
    // not depend on `buffer` afterward
    return json_document::parse_copy(buffer);
}

int main()
{
    std::cout << std::boolalpha;

    json_document doc = parse_from_temporary_buffer();
    std::cout << doc.owns_source() << '\n';
    std::cout << doc.root().is_object() << '\n';
}

Output:

true
true

Version history¶

Added in version 3.13.0 unreleased.