JSON for Modern C++  3.6.1

◆ is_discarded()

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>
constexpr bool nlohmann::basic_json::is_discarded ( ) const
inlinenoexcept

This function returns true if and only if the JSON value was discarded during parsing with a callback function (see parser_callback_t).

Note
This function will always be false for JSON values after parsing. That is, discarded values can only occur during parsing, but will be removed when inside a structured value or replaced by null in other cases.
Returns
true if type is discarded, false otherwise.
Complexity
Constant.
Exception safety
No-throw guarantee: this member function never throws exceptions.
Example
The following code exemplifies is_discarded() for all JSON types.
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_null;
10  json j_boolean = true;
11  json j_number_integer = 17;
12  json j_number_unsigned_integer = 12345678987654321u;
13  json j_number_float = 23.42;
14  json j_object = {{"one", 1}, {"two", 2}};
15  json j_array = {1, 2, 4, 8, 16};
16  json j_string = "Hello, world";
17 
18  // call is_discarded()
19  std::cout << std::boolalpha;
20  std::cout << j_null.is_discarded() << '\n';
21  std::cout << j_boolean.is_discarded() << '\n';
22  std::cout << j_number_integer.is_discarded() << '\n';
23  std::cout << j_number_unsigned_integer.is_discarded() << '\n';
24  std::cout << j_number_float.is_discarded() << '\n';
25  std::cout << j_object.is_discarded() << '\n';
26  std::cout << j_array.is_discarded() << '\n';
27  std::cout << j_string.is_discarded() << '\n';
28 }
basic_json<> json
default JSON class
Definition: json.hpp:871

Output (play with this example online):
false
false
false
false
false
false
false
false
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/is_discarded.cpp -o is_discarded 
Since
version 1.0.0

Definition at line 15095 of file json.hpp.