emplace_back()

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer, class BinaryType = std::vector<std::uint8_t>>

template<class... Args>

reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::emplace_back ( Args &&...  args )

inline

add an object to an array

Creates a JSON value from the passed parameters args to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending the value created from args.

Parameters

[in]

args

arguments to forward to a constructor of basic_json

Template Parameters

Args	compatible types to create a basic_json object

Returns

reference to the inserted element

Exceptions

type_error.311

when called on a type other than JSON array or null; example: "cannot use emplace_back() with number"

@complexity Amortized constant.

@liveexample{The example shows how push_back() can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,emplace_back}

Since

version 2.0.8, returns reference since 3.7.0

Definition at line 23342 of file json.hpp.

    {
        // emplace_back only works for null objects or arrays
        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
        {
            JSON_THROW(type_error::create(311, "cannot use emplace_back() with " + std::string(type_name()), *this));
        }
 
        // transform null object into an array
        if (is_null())
        {
            m_type = value_t::array;
            m_value = value_t::array;
            assert_invariant();
        }
 
        // add element to array (perfect forwarding)
        const auto old_capacity = m_value.array->capacity();
        m_value.array->emplace_back(std::forward<Args>(args)...);
        return set_parent(m_value.array->back(), old_capacity);
    }