Difference between "return 0" and "exit (0)"

Question

Is there any difference between return 0 and exit (0) when using in a function? If yes, When should I use return 0 or exit (0) in a function?

exit 0? probably doesn't compile. exit(0) exits your program. You probably don't want that — FDinoff, Jun 29 '13 at 17:46
There is a similar post here http://stackoverflow.com/questions/1116493/how-to-quit-a-c-program — doctorlove, Jun 29 '13 at 17:48
Was it really that hard to write a 10-line code to try it yourself? — i Code 4 Food, Jun 29 '13 at 17:50
Not sure why people use return(x) when return is not a function. See http://stackoverflow.com/questions/161879/parenthesis-surrounding-return-values — jarmod, Jun 29 '13 at 17:53
@Arthur "try it" is often a bad way to fully understand C, and I think this is one of that cases. About the question, they are different even in `main`, look at [these](http://stackoverflow.com/questions/17262698/can-main-return-structure/17262704#comment25021781_17262704) comments. — effeffe, Jun 29 '13 at 17:57

ouah · Accepted Answer · 2013-06-29T17:54:30.240

31

return exits from the function while exit exits from the program.

In main function executing return 0; statement or calling exit(0) function will call the registered atexit handlers and will cause program termination.

edited Jun 29 '13 at 17:54

answered Jun 29 '13 at 17:46

ouah

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The `atexit` handlers get called when returning from main, too. – Carl Norum Jun 29 '13 at 17:47

score 12 · Answer 2 · edited Oct 16 '18 at 05:26

exit 0 is a syntax error in C. You can have exit(0) that is instead a call to a standard library function.

The function exit will quit the whole program, returning the provided exit code to the OS. The return statement instead only quits the current function giving the caller the specified result.

They are the same only when used in main (because quitting the main function will terminate the program).

Normally exit is only used in emergency cases where you want to terminate the program because there's no sensible way to continue execution. For example:

//
// Ensure allocation of `size` bytes (will never return
// a NULL pointer to the caller).
//
// Too good to be true? Here's the catch: in case of memory
// exhaustion the function will not return **at all** :-)
//
void *safe_malloc(int size) {
    void *p = malloc(size);
    if (!p) {
        fprintf(stderr, "Out of memory: quitting\n");
        exit(1);
    }
    return p;
}

In this case if function a calls function b that calls function c that calls safe_malloc you may want to quit the program on the spot instead of returning to c an error code (e.g. a NULL pointer) if the code is not written to handle allocation failures.

score 8 · Answer 3 · answered Jun 29 '13 at 17:47

Yes there is, since there is no statement called exit. I guess you mean the function exit?

In that case, there is a big difference: The exit function exits the process, in other words the program is terminated. The return statement simply return from the current function.

They are only similar if used in the main function.

0decimal0 · Answer 4 · 2013-07-23T14:22:40.857

0

return is a statement that returns control back to the calling function.
exit is a system call which terminates the current process i.e the currently executing program.

In main() the return 0; and exit(0); perform the same thing.

NOTE: you have to include #include<stdlib.h>.

edited Jul 23 '13 at 14:22

answered Jun 29 '13 at 17:49

0decimal0

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*"Some compilers even accept and compile the code even if u dont write return 0"* because it's standard. – effeffe Jun 29 '13 at 17:55

Difference between "return 0" and "exit (0)"

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