Skip to content

# 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

Writing data to the referee of the result yields an undefined state.

## 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 (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.

Last update: May 1, 2022
Back to top