Check if OS X is running in 32 or 64-bit mode.

check64bit.c

/* File: check64bit.c
 * Description: Check if the running version of Mac OS X is 64-bit
 * To Compile: gcc -Wall -o check64bit check64bit.c
 * To run: ./check64bit
 */
 
#include <stdio.h>
#include <string.h>
#include <sys/utsname.h>

int main(int argc, char *argv[])
{
	int ret = 0;
	struct utsname uname_info;
	
	ret = uname(&uname_info);
	
	if (ret == 0)
	{
		printf("Uname Info\n");
		printf("Sysname  : %s\n", uname_info.sysname);
		printf("Nodename : %s\n", uname_info.nodename);
		printf("Release  : %s\n", uname_info.release);
		printf("Version  : %s\n", uname_info.version);
		printf("Machine  : %s\n", uname_info.machine);
		
		if (strcmp(uname_info.machine, "x86_64") == 0)
		{
			printf("You are running in 64-bit mode!\n");
		}
		else
		{
			printf("You are running in 32-bit mode.\n");
		}
	}
	
	return 0;
}