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◆ operator ValueType()
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 not std::is_same< ValueType, typename std::string_view >::value and detail::is_detected< detail::get_template_function, const basic_json_t &, ValueType >::value, int >::type = 0>
nlohmann::basic_json::operator ValueType |
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const |
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inline |
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';
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 17476 of file json.hpp.
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