JSON for Modern C++ 2.1.1

allocator_type
array
array_t
at
at
at
at
at
at
back
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basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
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~basic_json
| ## ◆ basic_json() [3/8] 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 CompatibleType , typename U = detail::uncvref_t<CompatibleType>, detail::enable_if_t< not std::is_base_of< std::istream, U >::value and not std::is_same< U, basic_json_t >::value and not detail::is_basic_json_nested_type< basic_json_t, U >::value and detail::has_to_json< basic_json, U >::value, int > = 0>
nlohmann::basic_json::basic_json | ( | CompatibleType && | val | ) |
| inline noexcept
  This is a "catch all" constructor for all compatible JSON types; that is, types for which a `to_json()` method exsits. The constructor forwards the parameter val to that method (to `json_serializer<U>to_json` method with `U = uncvref_t<CompatibleType>`, to be exact). Template type CompatibleType includes, but is not limited to, the following types: arrays: array_t and all kinds of compatible containers such as `std::vector`, `std::deque`, `std::list`, `std::forward_list`, `std::array`, `std::set`, `std::unordered_set`, `std::multiset`, and `unordered_multiset` with a `value_type` from which a basic_json value can be constructed. objects: object_t and all kinds of compatible associative containers such as `std::map`, `std::unordered_map`, `std::multimap`, and `std::unordered_multimap` with a `key_type` compatible to string_t and a `value_type` from which a basic_json value can be constructed. strings: string_t, string literals, and all compatible string containers can be used. numbers: number_integer_t, number_unsigned_t, number_float_t, and all convertible number types such as `int`, `size_t`, `int64_t`, `float` or `double` can be used. boolean: boolean_t / `bool` can be used. See the examples below. Template Parameters
  CompatibleType | a type such that: CompatibleType is not derived from `std::istream`, CompatibleType is not basic_json (to avoid hijacking copy/move constructors), CompatibleType is not a basic_json nested type (e.g., json_pointer, iterator, etc ...) json_serializer<U> has a `to_json(basic_json_t&, CompatibleType&&)` method
  U | = `uncvref_t<CompatibleType>`
  Parameters
  [in] | val | the value to be forwarded
  Complexity Usually linear in the size of the passed val, also depending on the implementation of the called `to_json()` method. Exceptions
  what | `json_serializer<U>to_json()` throws
  Example The following code shows the constructor with several compatible types. 1 #include "json.hpp" 2 #include <deque> 3 #include <list> 4 #include <forward_list> 5 #include <set> 6 #include <unordered_map> 7 #include <unordered_set> 8 9 using json = nlohmann::json; 10 11 int main() 12 { 13 // ============ 14 // object types 15 // ============ 16 17 // create an object from an object_t value 18 json::object_t object_value = { {"one", 1}, {"two", 2} }; 19 json j_object_t(object_value); 20 21 // create an object from std::map 22 std::map<std::string, int> c_map 23 { 24 {"one", 1}, {"two", 2}, {"three", 3} 25 }; 26 json j_map(c_map); 27 28 // create an object from std::unordered_map 29 std::unordered_map<const char*, double> c_umap 30 { 31 {"one", 1.2}, {"two", 2.3}, {"three", 3.4} 32 }; 33 json j_umap(c_umap); 34 35 // create an object from std::multimap 36 std::multimap<std::string, bool> c_mmap 37 { 38 {"one", true}, {"two", true}, {"three", false}, {"three", true} 39 }; 40 json j_mmap(c_mmap); // only one entry for key "three" is used 41 42 // create an object from std::unordered_multimap 43 std::unordered_multimap<std::string, bool> c_ummap 44 { 45 {"one", true}, {"two", true}, {"three", false}, {"three", true} 46 }; 47 json j_ummap(c_ummap); // only one entry for key "three" is used 48 49 // serialize the JSON objects 50 std::cout << j_object_t << '\n'; 51 std::cout << j_map << '\n'; 52 std::cout << j_umap << '\n'; 53 std::cout << j_mmap << '\n'; 54 std::cout << j_ummap << "\n\n"; 55 56 57 // =========== 58 // array types 59 // =========== 60 61 // create an array from an array_t value 62 json::array_t array_value = {"one", "two", 3, 4.5, false}; 63 json j_array_t(array_value); 64 65 // create an array from std::vector 66 std::vector<int> c_vector {1, 2, 3, 4}; 67 json j_vec(c_vector); 68 69 // create an array from std::deque 70 std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6}; 71 json j_deque(c_deque); 72 73 // create an array from std::list 74 std::list<bool> c_list {true, true, false, true}; 75 json j_list(c_list); 76 77 // create an array from std::forward_list 78 std::forward_list<int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543}; 79 json j_flist(c_flist); 80 81 // create an array from std::array 82 std::array<unsigned long, 4> c_array {{1, 2, 3, 4}}; 83 json j_array(c_array); 84 85 // create an array from std::set 86 std::set<std::string> c_set {"one", "two", "three", "four", "one"}; 87 json j_set(c_set); // only one entry for "one" is used 88 89 // create an array from std::unordered_set 90 std::unordered_set<std::string> c_uset {"one", "two", "three", "four", "one"}; 91 json j_uset(c_uset); // only one entry for "one" is used 92 93 // create an array from std::multiset 94 std::multiset<std::string> c_mset {"one", "two", "one", "four"}; 95 json j_mset(c_mset); // both entries for "one" are used 96 97 // create an array from std::unordered_multiset 98 std::unordered_multiset<std::string> c_umset {"one", "two", "one", "four"}; 99 json j_umset(c_umset); // both entries for "one" are used 100 101 // serialize the JSON arrays 102 std::cout << j_array_t << '\n'; 103 std::cout << j_vec << '\n'; 104 std::cout << j_deque << '\n'; 105 std::cout << j_list << '\n'; 106 std::cout << j_flist << '\n'; 107 std::cout << j_array << '\n'; 108 std::cout << j_set << '\n'; 109 std::cout << j_uset << '\n'; 110 std::cout << j_mset << '\n'; 111 std::cout << j_umset << "\n\n"; 112 113 114 // ============ 115 // string types 116 // ============ 117 118 // create string from a string_t value 119 json::string_t string_value = "The quick brown fox jumps over the lazy dog."; 120 json j_string_t(string_value); 121 122 // create a JSON string directly from a string literal 123 json j_string_literal("The quick brown fox jumps over the lazy dog."); 124 125 // create string from std::string 126 std::string s_stdstring = "The quick brown fox jumps over the lazy dog."; 127 json j_stdstring(s_stdstring); 128 129 // serialize the JSON strings 130 std::cout << j_string_t << '\n'; 131 std::cout << j_string_literal << '\n'; 132 std::cout << j_stdstring << "\n\n"; 133 134 135 // ============ 136 // number types 137 // ============ 138 139 // create a JSON number from number_integer_t 140 json::number_integer_t value_integer_t = -42; 141 json j_integer_t(value_integer_t); 142 143 // create a JSON number from number_unsigned_t 144 json::number_integer_t value_unsigned_t = 17; 145 json j_unsigned_t(value_unsigned_t); 146 147 // create a JSON number from an anonymous enum 148 enum { enum_value = 17 }; 149 json j_enum(enum_value); 150 151 // create values of different integer types 152 short n_short = 42; 153 int n_int = -23; 154 long n_long = 1024; 155 int_least32_t n_int_least32_t = -17; 156 uint8_t n_uint8_t = 8; 157 158 // create (integer) JSON numbers 159 json j_short(n_short); 160 json j_int(n_int); 161 json j_long(n_long); 162 json j_int_least32_t(n_int_least32_t); 163 json j_uint8_t(n_uint8_t); 164 165 // create values of different floating-point types 166 json::number_float_t v_ok = 3.141592653589793; 167 json::number_float_t v_nan = NAN; 168 json::number_float_t v_infinity = INFINITY; 169 170 // create values of different floating-point types 171 float n_float = 42.23; 172 float n_float_nan = 1.0f / 0.0f; 173 double n_double = 23.42; 174 175 // create (floating point) JSON numbers 176 json j_ok(v_ok); 177 json j_nan(v_nan); 178 json j_infinity(v_infinity); 179 json j_float(n_float); 180 json j_float_nan(n_float_nan); 181 json j_double(n_double); 182 183 // serialize the JSON numbers 184 std::cout << j_integer_t << '\n'; 185 std::cout << j_unsigned_t << '\n'; 186 std::cout << j_enum << '\n'; 187 std::cout << j_short << '\n'; 188 std::cout << j_int << '\n'; 189 std::cout << j_long << '\n'; 190 std::cout << j_int_least32_t << '\n'; 191 std::cout << j_uint8_t << '\n'; 192 std::cout << j_ok << '\n'; 193 std::cout << j_nan << '\n'; 194 std::cout << j_infinity << '\n'; 195 std::cout << j_float << '\n'; 196 std::cout << j_float_nan << '\n'; 197 std::cout << j_double << "\n\n"; 198 199 200 // ============= 201 // boolean types 202 // ============= 203 204 // create boolean values 205 json j_truth = true; 206 json j_falsity = false; 207 208 // serialize the JSON booleans 209 std::cout << j_truth << '\n'; 210 std::cout << j_falsity << '\n'; 211 } nlohmann::basic_json::number_float_t NumberFloatType number_float_t a type for a number (floating-point) Definition: json.hpp:1889 nlohmann::json basic_json<> json default JSON class Definition: json.hpp:13933 nlohmann::basic_json::object_t ObjectType< StringType, basic_json, std::less< StringType >, AllocatorType< std::pair< const StringType, basic_json > >> object_t a type for an object Definition: json.hpp:1553 nlohmann::basic_json::number_integer_t NumberIntegerType number_integer_t a type for a number (integer) Definition: json.hpp:1750 nlohmann::basic_json::array_t ArrayType< basic_json, AllocatorType< basic_json > > array_t a type for an array Definition: json.hpp:1599 nlohmann::basic_json::string_t StringType string_t a type for a string Definition: json.hpp:1652 Output (play with this example online):
      {"one":1,"two":2}
      {"one":1,"three":3,"two":2}
      {"one":1.2,"three":3.4,"two":2.3}
      {"one":true,"three":false,"two":true}
      {"one":true,"three":false,"two":true}

      ["one","two",3,4.5,false]
      [1,2,3,4]
      [1.2,2.3,3.4,5.6]
      [true,true,false,true]
      [12345678909876,23456789098765,34567890987654,45678909876543]
      [1,2,3,4]
      ["four","one","three","two"]
      ["four","three","two","one"]
      ["four","one","one","two"]
      ["four","two","one","one"]

      "The quick brown fox jumps over the lazy dog."
      "The quick brown fox jumps over the lazy dog."
      "The quick brown fox jumps over the lazy dog."

      -42
      17
      17
      42
      -23
      1024
      -17
      8
      3.14159265358979
      null
      null
      42.2299995422363
      null
      23.42

      true
      false
  The example code above can be translated with
      g++ -std=c++11 -Isrc doc/examples/basic_json__CompatibleType.cpp -o basic_json__CompatibleType
Since version 2.1.0 Definition at line 2274 of file json.hpp.