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Type support

See also type system overview and arithmetic types defined by the language.

Basic types

Additional basic types and convenience macros

Defined in header <stddef.h>
unsigned integer type returned by the sizeof operator
(typedef)
signed integer type returned when subtracting two pointers
(typedef)
(C23)
the type of the predefined null pointer constant nullptr
(typedef)
implementation-defined null pointer constant
(macro constant)
(C11)
a type with alignment requirement as great as any other scalar type
(typedef)
byte offset from the beginning of a struct type to specified member
(function macro)
Defined in header <stdbool.h>
bool
(C99)(removed in C23)
convenience macro, expands to _Bool
(keyword macro)
true
(C99)(removed in C23)
expands to integer constant 1
(macro constant)
false
(C99)(removed in C23)
expands to integer constant 0
(macro constant)
__bool_true_false_are_defined
(C99)(deprecated in C23)
expands to integer constant 1
(macro constant)
Defined in header <stdalign.h>
alignas
(C11)(removed in C23)
convenience macro, expands to keyword _Alignas
(keyword macro)
alignof
(C11)(removed in C23)
convenience macro, expands to keyword _Alignof
(keyword macro)
__alignas_is_defined
(C11)(removed in C23)
expands to integer constant 1
(macro constant)
__alignof_is_defined
(C11)(removed in C23)
expands to integer constant 1
(macro constant)
Defined in header <stdnoreturn.h>
noreturn
(C11)(deprecated in C23)
convenience macro, expands to _Noreturn
(keyword macro)

Fixed width integer types (since C99)

Numeric limits

Notes

The type of true and false is int rather than _Bool.

A program may undefine and perhaps then redefine the macros bool, true and false. However, such ability is a deprecated feature.

 (since C99)
(until C23)

The type of true and false is bool. It is unspecified whether any of bool, _Bool, true, or false is implemented as a predefined macro.

If bool, true, or false (but not _Bool) is defined as a predefined macro, a program may undefine and perhaps redefine it.

 (since C23)

Example

#include <stdio.h>
#include <stdbool.h>
#include <stdalign.h>
 
int main(void)
{
    printf("%d %d %d\n", true && false, true || false, !false);
    printf("%d %d\n", true ^ true, true + true);
    printf("%zu\n", alignof(short));
}

Possible output:

0 1 1
0 2
2

References

  • C17 standard (ISO/IEC 9899:2018):
    • 7.15 Alignment <stdalign.h> (p: 196)
    • 7.18 Boolean type and values <stdbool.h> (p: 210)
    • 7.19 Common definitions <stddef.h> (p: 211)
    • 7.23 _Noreturn <stdnoreturn.h> (p: 263)
    • 7.31.9 Boolean type and values <stdbool.h> (p: 332)
  • C11 standard (ISO/IEC 9899:2011):
    • 7.15 Alignment <stdalign.h> (p: 268)
    • 7.18 Boolean type and values <stdbool.h> (p: 287)
    • 7.19 Common definitions <stddef.h> (p: 288)
    • 7.23 _Noreturn <stdnoreturn.h> (p: 361)
    • 7.31.9 Boolean type and values <stdbool.h> (p: 456)
  • C99 standard (ISO/IEC 9899:1999):
    • 7.18 Boolean type and values <stdbool.h> (p: 253)
    • 7.19 Common definitions <stddef.h> (p: 254)
    • 7.26.7 Boolean type and values <stdbool.h> (p: 401)
  • C89/C90 standard (ISO/IEC 9899:1990):
    • 4.1.5 Common definitions <stddef.h>

See also

C++ documentation for Type support library

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