What's the scenario to use atexit function?

Question

CRT function atexit() could register a function to run after main function returns. I am wondering what's the typical scenario to use this? Is it (atexit) really necessary?

Answer 1

I guess its primary use is when you don't have control over main and you want to make sure something is called at the end of it.

It's sometimes used by libraries that don't want to insist that the user program calls their cleanup functions explicitly before terminating the program.

It's also used in the phoenix singleton pattern (see Modern C++ Design by Andrei Alexandrescu).

Answer 2

It can be used for what you want that need to be executed EVERYTIME an application is shutting down. By using that, you don't need to bloat your code by adding all the cleanup code before each exit() you can find in your code.

Some use cases :

• Clean a temporary folder
• Print a memory dump

Answer 3

One of the main uses of atexit is for libraries to perform cleanup on program exit. Note that atexit is called when exit is called, not when the program aborts or crashes, so you can't do cleanup on assertion failures and so on. It is also not called if the program calls exec.

You can call it directly in the main program if you want, if you have a library that might call exit for some reason.

Note that you can only register a limited number of atexit handlers, where 'limited' depends on your operating system, and so it returns an error status.

It gives C programs a similar ability to calling the destructor of a static variable in C++.

I've used it to delete temporary files, or (once or twice) to reset some hardware registers. Generally it's not necessary to use it to close files or rlease memory, because the O/S will do that for you.