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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 >
Implict type conversion between the JSON value and a compatible value. The call is realized by calling get() const.
- Template Parameters
-
ValueType | 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, thrown by get() const |
- 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 bool v1 = json_types[ "boolean"];
25 int v2 = json_types[ "number"][ "integer"];
26 short v3 = json_types[ "number"][ "integer"];
27 float v4 = json_types[ "number"][ "floating-point"];
28 int v5 = json_types[ "number"][ "floating-point"];
29 std::string v6 = json_types[ "string"];
30 std::vector<short> v7 = json_types[ "array"];
31 std::unordered_map<std::string, json> v8 = json_types;
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:121
namespace for Niels Lohmann Definition: json.hpp:56
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 withg++ -std=c++11 -Isrc doc/examples/operator__ValueType.cpp -o operator__ValueType .
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