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◆ operator ValueType()
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 , typename std::enable_if< not std::is_pointer< ValueType >::value and not std::is_same< ValueType, detail::json_ref< basic_json >>::value and not std::is_same< ValueType, typename string_t::value_type >::value and not detail::is_basic_json< ValueType >::value and not std::is_same< ValueType, std::initializer_list< typename string_t::value_type >>::value and detail::is_detected< detail::get_template_function, const basic_json_t &, ValueType >::value, int >::type = 0>
Implicit type conversion between the JSON value and a compatible value. The call is realized by calling get() const.
- 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. The character type of string_t as well as an initializer list of this type is excluded to avoid ambiguities as these types implicitly convert to std::string . |
- Returns
- copy of the JSON value, converted to type ValueType
- Exceptions
-
type_error.302 | in case passed type ValueType is incompatible to the JSON value type (e.g., the JSON value is of type boolean, but a string is requested); see example below |
- 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> . ^^ 2 #include <unordered_map> 3 #include <nlohmann/json.hpp> 16 { "floating-point", 17.23} 19 { "string", "Hello, world!"}, 20 { "array", {1, 2, 3, 4, 5}}, 25 bool v1 = json_types[ "boolean"]; 26 int v2 = json_types[ "number"][ "integer"]; 27 short v3 = json_types[ "number"][ "integer"]; 28 float v4 = json_types[ "number"][ "floating-point"]; 29 int v5 = json_types[ "number"][ "floating-point"]; 30 std::string v6 = json_types[ "string"]; 31 std::vector<short> v7 = json_types[ "array"]; 32 std::unordered_map<std::string, json> v8 = json_types; 35 std::cout << v1 << '\n'; 36 std::cout << v2 << ' ' << v3 << '\n'; 37 std::cout << v4 << ' ' << v5 << '\n'; 38 std::cout << v6 << '\n'; 42 std::cout << i << ' '; 48 std::cout << i.first << ": " << i.second << '\n'; 54 bool v1 = json_types[ "string"]; 58 std::cout << e.what() << '\n'; basic_json<> json default JSON class
detail::type_error type_error exception indicating executing a member function with a wrong type
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]
[json.exception.type_error.302] type must be boolean, but is string
^^ The example code above can be translated withg++ -std=c++11 -Isingle_include doc/examples/operator__ValueType.cpp -o operator__ValueType
- Since
- version 1.0.0
Definition at line 15250 of file json.hpp.
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