JSON for Modern C++ 3.0

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~basic_json
| 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 = int64_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
  ValueType | non-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_error | in case passed type ValueType is incompatible to JSON
  Complexity Linear in the size of the JSON value. Example The example below shows serveral 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++ assiciative containers such as `std::unordered_map<std::string, json>`. 1 #include <json.hpp> 2 #include <unordered_map> 3 4 using namespace nlohmann; 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 } nlohmann::basic_json a class to store JSON values Definition: json.hpp:121 nlohmann namespace for Niels Lohmann Definition: json.hpp:56 nlohmann::basic_json::get ValueType get() const get a value (explicit) Definition: json.hpp:1938 Output:
      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