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>
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. ^^
2 #include <nlohmann/json.hpp> 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";
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';
basic_json<> json
default JSON class
Output (play with this example online):^^ false
false
false
false
false
false
false
false
^^ The example code above can be translated withg++ -std=c++11 -Isingle_include doc/examples/is_discarded.cpp -o is_discarded
- Since
- version 1.0.0
Definition at line 14708 of file json.hpp.