nlohmann::basic_json_document::is_discarded¶

bool is_discarded() const noexcept;

Returns whether the document holds no value, either because it was default-constructed or because the last call to parse(), parse_copy(), or read() failed with allow_exceptions set to false.

Return value¶

true if the document is discarded, false otherwise.

Exception safety¶

No-throw guarantee: this function never throws exceptions.

Complexity¶

Constant.

Notes¶

When the document is discarded, root() returns a discarded view (its is_discarded() is also true).

Examples¶

Example

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

using json_document = nlohmann::json_document;

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

    // with allow_exceptions == false, a parse error produces a discarded
    // document instead of throwing -- exactly like basic_json::parse()
    json_document doc = json_document::parse(R"({"a": )", /* allow_exceptions */ false);
    std::cout << doc.is_discarded() << '\n';
    std::cout << doc.root().is_discarded() << '\n';

    // a successful parse is never discarded
    json_document ok = json_document::parse(R"({"a": 1})", false);
    std::cout << ok.is_discarded() << '\n';
}

Output:

true
true
false

Version history¶

Added in version 3.13.0 unreleased.