In GCC C compiler, we have nice feature to execute the certain function before and after main( ). So some startup code can be executed before main( ) starts, and some cleanup code can be executed after main() ends. For example, in the following program, StartupFunction( ) is called before main( ) and CleanupFunction( ) is called after main( ).
#include<stdio.h>
/* Apply the constructor attribute to StartupFunction() so that it
is executed before main() */
void StartupFunction(void) __attribute__ ((constructor));
/* Apply the destructor attribute to CleanupFunction() so that it
is executed after main() */
void CleanupFunction(void) __attribute__ ((destructor));
/* implementation of StartupFunction*/
void StartupFunction(void)
{
printf ("startup code before main()\n");
}
/* implementation of CleanupFunctiom */
void CleanupFunction(void)
{
printf ("cleanup code after main()\n");
}
int main (void)
{
printf ("hello\n");
return 0;
}
Output
