JSON for Modern C++ 2.1.1
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◆ get() [3/5]

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>
template<typename ValueTypeCV , typename ValueType = detail::uncvref_t<ValueTypeCV>, detail::enable_if_t< not std::is_same< basic_json_t, ValueType >::value and detail::has_from_json< basic_json_t, ValueType >::value and not detail::has_non_default_from_json< basic_json_t, ValueType >::value, int > = 0>
ValueType nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::get ( ) const
inlinenoexcept

Explicit type conversion between the JSON value and a compatible value which is CopyConstructible and DefaultConstructible. The value is converted by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

JSONSerializer<ValueType>::from_json(*this, ret);
return ret;
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Definition json.hpp:2165

This overloads is chosen if:

Template Parameters
ValueTypeCVthe provided value type
ValueTypethe returned value type
Returns
copy of the JSON value, converted to ValueType
Exceptions
whatjson_serializer<ValueType> from_json() method throws
Example\n The example below shows several conversions from JSON values
to other types. There a few things to note: (1) Floating-point numbers can be converted to integers, (2) A JSON array can be converted to a standard std::vector<short>, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string, json>.
1#include <json.hpp>
2#include <unordered_map>
3
4using json = nlohmann::json;
5
6int main()
7{
8 // create a JSON value with different types
10 {
11 {"boolean", true},
12 {
13 "number", {
14 {"integer", 42},
15 {"floating-point", 17.23}
16 }
17 },
18 {"string", "Hello, world!"},
19 {"array", {1, 2, 3, 4, 5}},
20 {"null", nullptr}
21 };
22
23 // use explicit conversions
24 auto v1 = json_types["boolean"].get<bool>();
25 auto v2 = json_types["number"]["integer"].get<int>();
26 auto v3 = json_types["number"]["integer"].get<short>();
27 auto v4 = json_types["number"]["floating-point"].get<float>();
28 auto v5 = json_types["number"]["floating-point"].get<int>();
29 auto v6 = json_types["string"].get<std::string>();
30 auto v7 = json_types["array"].get<std::vector<short>>();
31 auto v8 = json_types.get<std::unordered_map<std::string, json>>();
32
33 // print the conversion results
34 std::cout << v1 << '\n';
35 std::cout << v2 << ' ' << v3 << '\n';
36 std::cout << v4 << ' ' << v5 << '\n';
37 std::cout << v6 << '\n';
38
39 for (auto i : v7)
40 {
41 std::cout << i << ' ';
42 }
43 std::cout << "\n\n";
44
45 for (auto i : v8)
46 {
47 std::cout << i.first << ": " << i.second << '\n';
48 }
49}
basic_json get() const
get special-case overload
Definition json.hpp:3173
a class to store JSON values
Definition json.hpp:1040
basic_json<> json
default JSON class
Definition json.hpp:12369

Output (play with this example online):
1
42 42
17.23 17
Hello, world!
1 2 3 4 5 

string: "Hello, world!"
number: {"floating-point":17.23,"integer":42}
null: null
boolean: true
array: [1,2,3,4,5]

The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/get__ValueType_const.cpp -o get__ValueType_const 
Since
version 2.1.0

Definition at line 3225 of file json.hpp.