Defined in header <stddef.h>
typedef /*implementation-defined*/ max_align_t;
(since C11)

max_align_t is a type whose alignment requirement is at least as strict (as large) as that of every scalar type.


Pointers returned by allocation functions such as malloc are suitably aligned for any object, which means they are aligned at least as strictly as max_align_t.

max_align_t is usually synonymous with the largest scalar type, which is long double on most platforms, and its alignment requirement is either 8 or 16.


#include <stdio.h>
#include <stddef.h>
#include <stdalign.h>
#include <stdlib.h>
#include <stdint.h>
#include <inttypes.h>
int main(void)
    size_t a = alignof(max_align_t);
    printf("Alignment of max_align_t is %zu (%#zx)\n", a, a);
    void *p = malloc(123);
    printf("The address obtained from malloc(123) is %#" PRIxPTR"\n",

Possible output:

Alignment of max_align_t is 16 (0x10)
The address obtained from malloc(123) is 0x1fa67010


  • C17 standard (ISO/IEC 9899:2018):
    • 7.19 Common definitions <stddef.h> (p: 211)
  • C11 standard (ISO/IEC 9899:2011):
    • 7.19 Common definitions <stddef.h> (p: 288)

See also

C++ documentation for max_align_t

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