With GCC family of C compilers, we can mark some functions to execute 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, myStartupFun() is called before main() and myCleanupFun() is called after main().
startup code before main() hello cleanup code after main()
Like the above feature, GCC has added many other interesting features to standard C language. See this for more details.
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Executing main() in C – behind the scene
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