Type support

 

C

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Strings library

Algorithms

Numerics

Date and time utilities

Input/output support

Localization support

Concurrency support (C11)

Technical Specifications

Symbol index

 

Type support

size_t

ptrdiff_t

NULL

max_align_t (C11)

offsetof

Numeric limits

Fixed width integer types (C99)

 

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>
size_t	unsigned integer type returned by the sizeof operator (typedef)
ptrdiff_t	signed integer type returned when subtracting two pointers (typedef)
NULL	implementation-defined null pointer constant (macro constant)
max_align_t (C11)	a type with alignment requirement as great as any other scalar type (typedef)
offsetof	byte offset from the beginning of a struct type to specified member (function macro)
Defined in header <stdbool.h>
bool (C99)(until C23)	convenience macro, expands to _Bool (keyword macro)
true (C99)(until C23)	expands to integer constant 1 (macro constant)
false (C99)(until 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)(until C23)	convenience macro, expands to keyword _Alignas (keyword macro)
alignof (C11)(until C23)	convenience macro, expands to keyword _Alignof (keyword macro)
__alignas_is_defined (C11)(until C23)	expands to integer constant 1 (macro constant)
__alignof_is_defined (C11)(until 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)

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

Run this code

#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>