How do you execute a function in C before the main function starts

In GCC, you can declare constructor and destructor using the attribute keyword as follows:

#include <stdio.h>
__attribute((constructor)) void before_main()
{
 printf("%s/n",__FUNCTION__);
}
__attribute((destructor)) void after_main()
{
 printf("%s/n",__FUNCTION__);
}
int main( int argc, char ** argv )
{
 printf("%s/n",__FUNCTION__);
 return 0;
}

  Vc does not support attribute keyword. In vc, the following method can be used:

#include <stdio.h>
int
main( int argc, char ** argv )
{
        printf("%s/n",__FUNCTION__);
        return 0;
}

int before_main()
{
        printf("%s/n",__FUNCTION__);
        return 0;
}
int after_main()
{
        printf("%s/n",__FUNCTION__);
        return 0;
}
typedef int func();
#pragma data_seg(".CRT$XIU")
static func * before[] = { before_main };
#pragma data_seg(".CRT$XPU")
static func * after[] = { after_main };
#pragma data_seg()

Compile and execute, the results of the above two pieces of code are:

before_main

The main

after_main

You can call multiple functions before and after main, declare multiple constructors, destructor under GCC using attributes, and add multiple function Pointers in before and after arrays under vc.