operator[]() [3/8]

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>>

reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::operator[] ( const typename object_t::key_type &  key )

inline

access specified object element

Returns a reference to the element at with specified key key.

Note

If key is not found in the object, then it is silently added to the object and filled with a null value to make key a valid reference. In case the value was null before, it is converted to an object.

Parameters

[in]

key

key of the element to access

Returns

reference to the element at key key

Exceptions

type_error.305

if the JSON value is not an object or null; in that cases, using the [] operator with a key makes no sense.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}

See also

see at(const typename object_t::key_type&) for access by reference with range checking

see value() for access by value with a default value

Since

version 1.0.0

Definition at line 21475 of file json.hpp.

    {
        // implicitly convert null value to an empty object
        if (is_null())
        {
            m_type = value_t::object;
            m_value.object = create<object_t>();
            assert_invariant();
        }
 
        // operator[] only works for objects
        if (JSON_HEDLEY_LIKELY(is_object()))
        {
            return set_parent(m_value.object->operator[](key));
        }
 
        JSON_THROW(type_error::create(305, "cannot use operator[] with a string argument with " + std::string(type_name()), *this));
    }