JSON for Modern C++  2.0.6

§ get() [1/3]

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 ValueType , typename std::enable_if< not std::is_pointer< ValueType >::value, int >::type = 0>
ValueType nlohmann::basic_json::get ( ) const
inline

Explicit type conversion between the JSON value and a compatible value.

Template Parameters
ValueTypenon-pointer type compatible to the JSON value, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays
Returns
copy of the JSON value, converted to type ValueType
Exceptions
std::domain_errorin case passed type ValueType is incompatible to JSON; example: "type must be object, but is null"
Complexity
Linear in the size of the JSON value.
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 <json.hpp>
2 #include <unordered_map>
3 
4 using json = nlohmann::json;
5 
6 int main()
7 {
8  // create a JSON value with different types
9  json json_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<> json
default JSON class
Definition: json.hpp:10155
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 
See also
operator ValueType() const for implicit conversion
get() for pointer-member access
Since
version 1.0.0

Definition at line 2901 of file json.hpp.