JSON for Modern C++  3.5.0

◆ items() [1/2]

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>
iteration_proxy<iterator> nlohmann::basic_json::items ( )
inlinenoexcept

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without items() function:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without items() function:

for (auto it : j_object)
{
// "it" is of type json::reference and has no key() member
std::cout << "value: " << it << '\n';
}

Range-based for loop with items() function:

for (auto& el : j_object.items())
{
std::cout << "key: " << el.key() << ", value:" << el.value() << '\n';
}

The items() function also allows to use structured bindings (C++17):

for (auto& [key, val] : j_object.items())
{
std::cout << "key: " << key << ", value:" << val << '\n';
}
Note
When iterating over an array, key() will return the index of the element as string (see example). For primitive types (e.g., numbers), key() returns an empty string.
Returns
iteration proxy object wrapping ref with an interface to use in range-based for loops
Example^^ The following code shows how the function is used. ^^ items.cpp
Output (play with this example online):^^
key: one, value: 1
key: two, value: 2
key: 0, value: 1
key: 1, value: 2
key: 2, value: 4
key: 3, value: 8
key: 4, value: 16
^^ The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/items.cpp -o items 
Exception safety^^ Strong guarantee: if an exception is thrown, there are no
changes in the JSON value.
Complexity^^ Constant.
Since
version 3.1.0, structured bindings support since 3.5.0.

Definition at line 16771 of file json.hpp.