nlohmann::basic_json::get_ref

template<typename ReferenceType>
ReferenceType get_ref();

template<typename ReferenceType>
const ReferenceType get_ref() const;

Implicit reference access to the internally stored JSON value. No copies are made.

Template parameters

ReferenceType : reference type; must be a reference to array_t, object_t, string_t, boolean_t, number_integer_t, or number_unsigned_t, number_float_t, or binary_t. Enforced by a static assertion.

Return value

reference to the internally stored JSON value if the requested reference type fits to the JSON value; throws type_error.303 otherwise

Exception safety

Strong exception safety: if an exception occurs, the original value stays intact.

Exceptions

Throws type_error.303 if the requested reference type does not match the stored JSON value type; example: "incompatible ReferenceType for get_ref, actual type is binary".

Complexity

Constant.

Notes

Undefined behavior

The reference becomes invalid if the underlying JSON object changes.

Examples

Example

The example shows several calls to get_ref().

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

using json = nlohmann::json;

int main()
{
    // create a JSON number
    json value = 17;

    // explicitly getting references
    auto r1 = value.get_ref<const json::number_integer_t&>();
    auto r2 = value.get_ref<json::number_integer_t&>();

    // print the values
    std::cout << r1 << ' ' << r2 << '\n';

    // incompatible type throws exception
    try
    {
        auto r3 = value.get_ref<json::number_float_t&>();
    }
    catch (const json::type_error& ex)
    {
        std::cout << ex.what() << '\n';
    }
}

Output:

17 17
[json.exception.type_error.303] incompatible ReferenceType for get_ref, actual type is number

Version history

Added in version 1.1.0.
Extended to binary types in version 3.8.0.

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