# Standard library header <cstdbool> (C++11)(until C++20), <stdbool.h> (C++11)

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This header was originally in the C standard library as `<stdbool.h>`.

Compatibility header. true, false and bool are keywords in C++, but they were not keywords in C until C23.

### Macros

__bool_true_false_are_defined (C++11)(deprecated) | C compatibility macro constant, expands to integer literal 1 (macro constant)

### Notes

`<cstdbool>` is deprecated in C++17 and removed in C++20. Corresponding `<stdbool.h>` is still available in C++20.

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 3827 | C++11 | C programs no longer need the compatibility macro `__bool_true_false_are_defined` since C23 | deprecated this macro in C++

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