JSON for Modern C++ 3.9.1

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~basic_json
| ## ◆ items() [2/2] 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, class BinaryType = std::vector<std::uint8_t>>
iteration_proxy<iterator> nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::items | ( |  | ) |
| inline noexcept
  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. Warning Using `items()` on temporary objects is dangerous. Make sure the object's lifetime exeeds the iteration. See https://github.com/nlohmann/json/issues/2040 for more information. 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. 1 #include <iostream> 2 #include <nlohmann/json.hpp> 3 4 using json = nlohmann::json; 5 6 int main() 7 { 8 // create JSON values 9 json j_object = {{"one", 1}, {"two", 2}}; 10 json j_array = {1, 2, 4, 8, 16}; 11 12 // example for an object 13 for (auto& x : j_object.items()) 14 { 15 std::cout << "key: " << x.key() << ", value: " << x.value() << '\n'; 16 } 17 18 // example for an array 19 for (auto& x : j_array.items()) 20 { 21 std::cout << "key: " << x.key() << ", value: " << x.value() << '\n'; 22 } 23 } 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 21389 of file json.hpp.

nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2940