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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>
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> .
2 #include <unordered_map>
15 { "floating-point", 17.23}
18 { "string", "Hello, world!"},
19 { "array", {1, 2, 3, 4, 5}},
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>>();
34 std::cout << v1 << '\n';
35 std::cout << v2 << ' ' << v3 << '\n';
36 std::cout << v4 << ' ' << v5 << '\n';
37 std::cout << v6 << '\n';
41 std::cout << i << ' ';
47 std::cout << i.first << ": " << i.second << '\n';
a class to store JSON values Definition: json.hpp:130
namespace for Niels Lohmann Definition: json.hpp:55
ValueType get() const get a value (explicit) Definition: json.hpp:2247
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 withg++ -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
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