push_back() [2/4]

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>>

void nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::push_back ( const basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType > &  val )

inline

add an object to an array

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

Parameters

[in]

val

the value to add to the JSON array

Exceptions

type_error.308

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

@complexity Amortized constant.

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

Since

version 1.0.0

Definition at line 23185 of file json.hpp.

    {
        // push_back only works for null objects or arrays
        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
        {
            JSON_THROW(type_error::create(308, "cannot use push_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
        const auto old_capacity = m_value.array->capacity();
        m_value.array->push_back(val);
        set_parent(m_value.array->back(), old_capacity);
    }