JSON for Modern C++  3.7.0

◆ get_to() [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>
template<typename ValueType , detail::enable_if_t< not detail::is_basic_json< ValueType >::value and detail::has_from_json< basic_json_t, ValueType >::value, int > = 0>
ValueType& nlohmann::basic_json::get_to ( ValueType &  v) const
inlinenoexcept

Explicit type conversion between the JSON value and a compatible value. The value is filled into the input parameter by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

ValueType v;
JSONSerializer<ValueType>::from_json(*this, v);

This overloads is chosen if:

Template Parameters
ValueTypethe input parameter type.
Returns
the input parameter, allowing chaining calls.
Exceptions
whatjson_serializer<ValueType> from_json() method throws
Example
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 <iostream>
2 #include <unordered_map>
3 #include <nlohmann/json.hpp>
4 
5 using json = nlohmann::json;
6 
7 int main()
8 {
9  // create a JSON value with different types
10  json json_types =
11  {
12  {"boolean", true},
13  {
14  "number", {
15  {"integer", 42},
16  {"floating-point", 17.23}
17  }
18  },
19  {"string", "Hello, world!"},
20  {"array", {1, 2, 3, 4, 5}},
21  {"null", nullptr}
22  };
23 
24  bool v1;
25  int v2;
26  short v3;
27  float v4;
28  int v5;
29  std::string v6;
30  std::vector<short> v7;
31  std::unordered_map<std::string, json> v8;
32 
33 
34  // use explicit conversions
35  json_types["boolean"].get_to(v1);
36  json_types["number"]["integer"].get_to(v2);
37  json_types["number"]["integer"].get_to(v3);
38  json_types["number"]["floating-point"].get_to(v4);
39  json_types["number"]["floating-point"].get_to(v5);
40  json_types["string"].get_to(v6);
41  json_types["array"].get_to(v7);
42  json_types.get_to(v8);
43 
44  // print the conversion results
45  std::cout << v1 << '\n';
46  std::cout << v2 << ' ' << v3 << '\n';
47  std::cout << v4 << ' ' << v5 << '\n';
48  std::cout << v6 << '\n';
49 
50  for (auto i : v7)
51  {
52  std::cout << i << ' ';
53  }
54  std::cout << "\n\n";
55 
56  for (auto i : v8)
57  {
58  std::cout << i.first << ": " << i.second << '\n';
59  }
60 }
basic_json<> json
default JSON class
Definition: json.hpp:2355

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 -Isingle_include doc/examples/get_to.cpp -o get_to 
Since
version 3.3.0

Definition at line 17087 of file json.hpp.