Detect system architecture (x86/x64) while running

Is it possible to detect the system/processor architecture while the program is runni开发者_StackOverflowng (under windows and under linux) in c++?

On Windows, you may use __cpuid. On Linux, you can open("/proc/cpuinfo") and look through it.

Here is an example on Windows, based on the example in the MSDN page:

#include <intrin.h>

bool cpuSupports64()
{
    int CPUInfo[4];
    __cpuid(CPUInfo, 0);
    return (CPUInfo[3] & 0x20000000) || false;
}

Under Linux, you can use the uname system call. It fills in this user-allocated struct:

  struct utsname {
           char sysname[];    /* Operating system name (e.g., "Linux") */
           char nodename[];   /* Name within "some implementation-defined
                                 network" */
           char release[];    /* OS release (e.g., "2.6.28") */
           char version[];    /* OS version */
           char machine[];    /* Hardware identifier */
       #ifdef _GNU_SOURCE
           char domainname[]; /* NIS or YP domain name */
       #endif
       };

The machine field will identify the architecture.

Depending on what you intend to do with this information (e.g. select the fastest handcoded assembly code for a specific CPU), under Linux you might want to read /proc/cpuinfo, specifically: the "flags" section, so you can choose between SSE/SSE2 implementation vs. MMX implementation vs. whatever.

Big endian system vs. little endian system is a bit more complicated, refer to: http://en.wikipedia.org/wiki/Endianess

You can also use Processor macros to detect system architecture in c++ code, for example:

#include <iostream>

int main()
{
#ifdef __x86_64__
    std::cout << "x86" << std::endl;
#endif

#ifdef __arm__
    std::cout << "arm" << std::endl;
#endif
}

Here is a reference list of Pre-defined Compiler Macros.

EDIT:Processor macros is compiler-independant, different compilers have different Processor macros, So it is not possible to detect system architecture this way.