AMD64

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Description

The AMD64 architecture as defined by AMD and Intel.

Macros

Type	Macro	Description
Identification	`__amd64____amd64__x86_64____x86_64`	Defined by GNU C and Sun Studio
Identification	`_M_X64_M_AMD64`	Defined by Visual Studio

Notes

Note that the x32 ABI can be detected by checking if the CPU uses the ILP32 data model.

Run-time checking:

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#include <stdio.h>

int
main(void)
{
  if (sizeof(int)    == 4 &&
      sizeof(long)   == 4 &&
      sizeof(void *) == 4)
  {
    printf("ILP32 detected (possibly x32 ABI)\n");
  } else {
    printf("Not ILP32\n");
  }

  return 0;
}

Compile-time checking:

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#include <stdio.h>

int
main(void)
{
#if __SIZEOF_INT__ == 4 && __SIZEOF_LONG__ == 4 && __SIZEOF_POINTER__ == 4
  printf("ILP32 detected\n");
#else
  printf("Not ILP32\n");
#endif

  return 0;
}

compile-time checking for systems that provide __ILP32__:

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#include <stdio.h>

int
main(void)
{
#if defined(__x86_64__) && defined(__ILP32__)
  printf("x32 ABI detected\n");
#else
  printf("Not x32 ABI\n");
#endif

  return 0;
}


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Created:	4 May 2026

AMD64

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Description

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Notes