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nlohmann
104 lines
2.9 KiB
Markdown
104 lines
2.9 KiB
Markdown
# nlohmann::basic_json::is_primitive
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```
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constexpr bool is_primitive() const noexcept;
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```
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This function returns `true` if and only if the JSON type is primitive (string, number, boolean, `null`, binary).
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## Return value
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`true` if type is primitive (string, number, boolean, `null`, or binary), `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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## Possible implementation
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```
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constexpr bool is_primitive() const noexcept
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{
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return is_null() || is_string() || is_boolean() || is_number() || is_binary();
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}
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```
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## Notes
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The term *primitive* stems from [RFC 8259](https://tools.ietf.org/html/rfc8259):
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> JSON can represent four primitive types (strings, numbers, booleans, and null) and two structured types (objects and arrays).
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This library extends primitive types to binary types, because binary types are roughly comparable to strings. Hence, `is_primitive()` returns `true` for binary values.
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## Examples
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Example
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The following code exemplifies `is_primitive()` 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 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_float = 23.42;
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json j_number_unsigned_integer = 12345678987654321u;
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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_primitive()
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std::cout << std::boolalpha;
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std::cout << j_null.is_primitive() << '\n';
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std::cout << j_boolean.is_primitive() << '\n';
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std::cout << j_number_integer.is_primitive() << '\n';
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std::cout << j_number_unsigned_integer.is_primitive() << '\n';
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std::cout << j_number_float.is_primitive() << '\n';
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std::cout << j_object.is_primitive() << '\n';
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std::cout << j_array.is_primitive() << '\n';
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std::cout << j_string.is_primitive() << '\n';
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std::cout << j_binary.is_primitive() << '\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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true
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true
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true
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true
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false
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false
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true
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true
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```
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## See also
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- [is_structured()](https://json.nlohmann.me/api/basic_json/is_structured/index.md) returns whether the JSON value is structured
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- [is_null()](https://json.nlohmann.me/api/basic_json/is_null/index.md) returns whether the JSON value is `null`
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- [is_string()](https://json.nlohmann.me/api/basic_json/is_string/index.md) returns whether the JSON value is a string
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- [is_boolean()](https://json.nlohmann.me/api/basic_json/is_boolean/index.md) returns whether the JSON value is a boolean
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- [is_number()](https://json.nlohmann.me/api/basic_json/is_number/index.md) returns whether the JSON value is a number
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- [is_binary()](https://json.nlohmann.me/api/basic_json/is_binary/index.md) returns whether the JSON value is a binary array
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## Version history
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- Added in version 1.0.0.
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- Extended to return `true` for binary types in version 3.8.0.
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