86 lines
2.1 KiB
Markdown
86 lines
2.1 KiB
Markdown
# nlohmann::basic_json::is_null
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```
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constexpr bool is_null() const noexcept;
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```
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This function returns `true` if and only if the JSON value is `null`.
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## Return value
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`true` if type is `null`, `false` otherwise.
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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 `is_null()` for all JSON types.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using 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_integer = 12345678987654321u;
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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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json j_binary = json::binary({1, 2, 3});
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// call is_null()
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std::cout << std::boolalpha;
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std::cout << j_null.is_null() << '\n';
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std::cout << j_boolean.is_null() << '\n';
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std::cout << j_number_integer.is_null() << '\n';
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std::cout << j_number_unsigned_integer.is_null() << '\n';
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std::cout << j_number_float.is_null() << '\n';
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std::cout << j_object.is_null() << '\n';
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std::cout << j_array.is_null() << '\n';
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std::cout << j_string.is_null() << '\n';
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std::cout << j_binary.is_null() << '\n';
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}
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```
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Output:
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```
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true
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false
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false
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false
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false
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false
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false
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false
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false
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```
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## See also
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- [`is_array`](https://json.nlohmann.me/api/basic_json/is_array/index.md) - checks whether the JSON value is an array
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- [`is_object`](https://json.nlohmann.me/api/basic_json/is_object/index.md) - checks whether the JSON value is an object
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- [`type`](https://json.nlohmann.me/api/basic_json/type/index.md) - returns the type of the JSON value
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- [`value_t`](https://json.nlohmann.me/api/basic_json/value_t/index.md) - the enumeration of JSON types
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- [`basic_json_view::is_null`](https://json.nlohmann.me/api/basic_json_view/is_null/index.md) - the same check on a zero-copy view
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- [Types](https://json.nlohmann.me/features/types/index.md) - the JSON value types and how they are stored
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## Version history
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- Added in version 1.0.0.
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