Functions that are executed before and after main() in C

Here we will see how to write a code where two functions are present, and one function will be executed before the main function, and another function will be executed after the main function. These features are used to do some startup task before executing the main, and some cleanup task after executing main.

To do this task we have to put attribute for these two functions. When the attribute is constructor attribute, then it will be executed before main(), and when the attribute is destructor type, then it will be executed after main().

Example Code

#include<stdio.h>
void before_main() __attribute__((constructor));
void after_main() __attribute__((destructor));
void before_main() {
   printf("This is executed before main.\n");
}
void after_main() {
   printf("This is executed after main.");
}
main() {
   printf("Inside main\n");
}

Output

This is executed before main.
Inside main
This is executed after main.