CODEWITHSUNDEEP
c
metro-man
metro-man

Reputation: 1803

How to check if the machine running on is 32 or 64 bit in C?

is there any preprocessor directive or other methods to check if the machine being run is 32 bit or 64 bit in C? I've tried googling this, but the problem with C is it brings up results for C#, C++, etc.. Also, I would prefer if this worked on Windows, Linux, and Mac.

Upvotes: 5

Views: 9024

Answers (5)

Peter
Peter

Reputation: 36617

The obvious way to do this at run time.

#include <limits.h>
#include <stdio.h>

int main()
{
     printf("%d bits\n", (int)(CHAR_BIT * sizeof(void *)));
     return 0;
}

Technically, this is not 100% guaranteed to work. Practically, this will work with most modern compilers - it is unusual for a void pointer to be represented using a number of bits that differs from that of the underlying system architecture.

To do a compile time check, there is no standard way. It is necessary to resort to macros that are specific to your compiler/preprocessor. You will therefore need to read relevant documentation.

Upvotes: 4

David C. Rankin
David C. Rankin

Reputation: 84642

You can use the following preprocessor directives to check if the machine is x86_64 in C. If it is 64-bit it sets the #define BUILD_64 flag. You then just check #ifdef BUILD_64 as the test throughout your code:

#if defined(__LP64__) || defined(_LP64)
# define BUILD_64   1
#endif

Upvotes: 1

teppic
teppic

Reputation: 8205

For Linux and OS X:

#include <sys/utsname.h>

struct utsname a;
uname (&a);

a->machine will be the string x86_64 on 64bit Intel machines, probably i586 or i686 on 32bit. You could do conditional compiling for these and whatever Windows uses.

Upvotes: 2

Shade
Shade

Reputation: 785

This isn't necessarily indicative of the machine that is running (read: not true when cross-compiling), but there are some preprocessor directives.

You can determine 32/64 bit from the architecture, the most common ones are:

// 64-bit
__x86_64__

// 32-bit
__i386__ ... __i686__

You can read a whole bunch of these here, for nearly any modernish processor:

http://sourceforge.net/p/predef/wiki/Architectures/

Upvotes: 2

thinkerou
thinkerou

Reputation: 1877

If this worked on Windows, I have some method.

  1. check whether the reg HKEY_CURRENT_USER\Software\Wow6432Node exists;

  2. check whether the file C:\Windows\SysWOW64 exists;

  3. use Windows API(IsWow64Process), please read MSDN.

Upvotes: 0

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