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106 lines
3.1 KiB
Markdown
106 lines
3.1 KiB
Markdown
# <small>nlohmann::basic_json::</small>operator value_t
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```cpp
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constexpr operator value_t() const noexcept;
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```
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Return the type of the JSON value as a value from the [`value_t`](value_t.md) enumeration.
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## Return value
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the type of the JSON value
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| Value type | return value |
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|---------------------------|----------------------------|
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| `#!json null` | `value_t::null` |
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| boolean | `value_t::boolean` |
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| string | `value_t::string` |
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| number (integer) | `value_t::number_integer` |
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| number (unsigned integer) | `value_t::number_unsigned` |
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| number (floating-point) | `value_t::number_float` |
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| object | `value_t::object` |
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| array | `value_t::array` |
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| binary | `value_t::binary` |
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| discarded | `value_t::discarded` |
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## Exception safety
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No-throw guarantee: this member function never throws exceptions.
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## Complexity
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Constant.
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## Examples
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??? example
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The following code exemplifies `operator value_t()` for all JSON types.
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```cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create JSON values
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json j_null;
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json j_boolean = true;
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json j_number_integer = -17;
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json j_number_unsigned = 42u;
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json j_number_float = 23.42;
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json j_object = {{"one", 1}, {"two", 2}};
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json j_array = {1, 2, 4, 8, 16};
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json j_string = "Hello, world";
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// call operator value_t()
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json::value_t t_null = j_null;
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json::value_t t_boolean = j_boolean;
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json::value_t t_number_integer = j_number_integer;
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json::value_t t_number_unsigned = j_number_unsigned;
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json::value_t t_number_float = j_number_float;
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json::value_t t_object = j_object;
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json::value_t t_array = j_array;
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json::value_t t_string = j_string;
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// print types
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std::cout << std::boolalpha;
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std::cout << (t_null == json::value_t::null) << '\n';
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std::cout << (t_boolean == json::value_t::boolean) << '\n';
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std::cout << (t_number_integer == json::value_t::number_integer) << '\n';
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std::cout << (t_number_unsigned == json::value_t::number_unsigned) << '\n';
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std::cout << (t_number_float == json::value_t::number_float) << '\n';
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std::cout << (t_object == json::value_t::object) << '\n';
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std::cout << (t_array == json::value_t::array) << '\n';
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std::cout << (t_string == json::value_t::string) << '\n';
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}
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```
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Output:
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```json
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true
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true
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true
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true
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true
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true
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true
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true
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```
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## See also
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- [type](type.md) named member function equivalent to this implicit conversion operator
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- [value_t](value_t.md) the enumeration of JSON types
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## Version history
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- Added in version 1.0.0.
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- Added unsigned integer type in version 2.0.0.
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- Added binary type in version 3.8.0.
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