[SOLVED] 64-bit version of GCC not compiling 64-bit exe

Issue

I am beginner regarding gcc command line compilation. I need a help regarding -m64 flag.

I installed gcc compiler using MinGW. I checked for gcc version by following, gcc -v command, which shows Target: x86_64-w64-mingw32. So I assume, 64-bit version of gcc is installed.

Objective: I wrote a small program to check, if the main.exe is generated for 32 or 64 bit.

#include<stdio.h>

int main(void)
{
    printf("The Size is: %lu\n", sizeof(long));
    
    return 0;   
}

I compiled using following command, gcc -o main main.c. When I execute the main.exe, it outputs, The Size is: 4.

But I expected the output to be `The Size is: 8'.

So i modified the command as gcc -m64 -o main main.c. When I executed the main.exe again, still it outputs `The Size is: 4'

How to compile for 64-bit version exe?

Solution

As others have said in the comments, the size of long can be 8 or 4 bytes on a 64bit system. You can try sizeof(size_t) or sizeof(void*). Even this might not be reliable on every system (but should work for Windows, Linux, macOS).

Answered By - Christian Halaszovich