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1# basic_json::get
2
3```cpp
4// (1)
5template<typename ValueType>
6ValueType get() const noexcept(
7    noexcept(JSONSerializer<ValueType>::from_json(
8        std::declval<const basic_json_t&>(), std::declval<ValueType&>())));
9
10// (2)
11template<typename BasicJsonType>
12BasicJsonType get() const;
13
14// (3)
15template<typename PointerType>
16PointerType get_ptr();
17
18template<typename PointerType>
19constexpr const PointerType get_ptr() const noexcept;
20```
21
221. Explicit type conversion between the JSON value and a compatible value which is
23   [CopyConstructible](https://en.cppreference.com/w/cpp/named_req/CopyConstructible) and
24   [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible). The value is converted by
25   calling the `json_serializer<ValueType>` `from_json()` method.
26
27    The function is equivalent to executing
28    ```cpp
29    ValueType ret;
30    JSONSerializer<ValueType>::from_json(*this, ret);
31    return ret;
32    ```
33
34    This overloads is chosen if:
35
36    - `ValueType` is not `basic_json`,
37    - `json_serializer<ValueType>` has a `from_json()` method of the form
38      `void from_json(const basic_json&, ValueType&)`, and
39    - `json_serializer<ValueType>` does not have a `from_json()` method of the form
40      `ValueType from_json(const basic_json&)`
41
42    If the type is **not** [CopyConstructible](https://en.cppreference.com/w/cpp/named_req/CopyConstructible) and
43    **not** [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible), the value is
44    converted by calling the `json_serializer<ValueType>` `from_json()` method.
45
46    The function is then equivalent to executing
47    ```cpp
48    return JSONSerializer<ValueTypeCV>::from_json(*this);
49    ```
50
51    This overloads is chosen if:
52
53    - `ValueType` is not `basic_json` and
54    - `json_serializer<ValueType>` has a `from_json()` method of the form
55     `ValueType from_json(const basic_json&)`
56
57    If `json_serializer<ValueType>` has both overloads of `from_json()`, the latter one is chosen.
58
592. Overload for `basic_json` specializations. The function is equivalent to executing
60    ```cpp
61    return *this;
62    ```
63
643. Explicit pointer access to the internally stored JSON value. No copies are made.
65
66## Template parameters
67
68`ValueType`
69:   the value type to return
70
71`BasicJsonType`
72:   a specialization of `basic_json`
73
74`PointerType`
75:   pointer type; must be a pointer to [`array_t`](array_t.md), [`object_t`](object_t.md), [`string_t`](string_t.md),
76    [`boolean_t`](boolean_t.md), [`number_integer_t`](number_integer_t.md), or
77    [`number_unsigned_t`](number_unsigned_t.md), [`number_float_t`](number_float_t.md), or [`binary_t`](binary_t.md).
78    Other types will not compile.
79
80## Return value
81
821. copy of the JSON value, converted to `ValueType`
832. a copy of `#!cpp *this`, converted into `BasicJsonType`
843. pointer to the internally stored JSON value if the requested pointer type fits to the JSON value; `#!cpp nullptr`
85   otherwise
86
87## Exceptions
88
89Depends on what `json_serializer<ValueType>` `from_json()` method throws
90
91## Notes
92
93!!! warning
94
95    Writing data to the pointee (overload 3) of the result yields an undefined state.
96
97## Example
98
99??? example
100
101    The example below shows several conversions from JSON values
102    to other types. There a few things to note: (1) Floating-point numbers can
103    be converted to integers, (2) A JSON array can be converted to a standard
104    `std::vector<short>`, (3) A JSON object can be converted to C++
105    associative containers such as `std::unordered_map<std::string, json>`.
106
107    ```cpp
108    --8<-- "examples/get__ValueType_const.cpp"
109    ```
110
111    Output:
112
113    ```json
114    --8<-- "examples/get__ValueType_const.output"
115    ```
116
117??? example
118
119    The example below shows how pointers to internal values of a JSON value can be requested. Note that no type
120    conversions are made and a `#cpp nullptr` is returned if the value and the requested pointer type does not match.
121
122    ```cpp
123    --8<-- "examples/get__PointerType.cpp"
124    ```
125
126    Output:
127
128    ```json
129    --8<-- "examples/get__PointerType.output"
130    ```
131
132## Version history
133
1341. Since version 2.1.0.
1352. Since version 2.1.0. Extended to work with other specializations of `basic_json` in version 3.2.0.
1363. Since version 1.0.0.
137