Difference between return 1, return 0, return -1 and exit?

Question

For example consider following code:

int main(int argc,char *argv[])
{
   int *p,*q;
   p = (int *)malloc(sizeof(int)*10);
   q = (int *)malloc(sizeof(int)*10);
   if (p == 0)
   {
      printf("ERROR: Out of memory\n");
      return 1;
   }

   
   if (q == 0)
   {
      printf("ERROR: Out of memory\n");
      exit(0);
   }
   
   return 0;
}

What does return 0, return 1, exit(0) do in the above program? exit(0) will exit total program and control comes out of loop but what happens in case of return 0, return 1, return -1.

You must also see this - [Difference between exit and return](http://stackoverflow.com/questions/3463551/difference-between-exit-and-return) — Suvarna Pattayil, Mar 24 '14 at 08:24
For one, `exit(0)` returning from a memory allocation failure gives someone a false sense of comfort, because it should almost certainly be `exit(EXIT_FAILURE)` (the program did, after all, just bomb a mem-alloc). — WhozCraig, Mar 24 '14 at 08:28
`exit` is a standard library function, so if you use it you need to #include , which isn't necessary if you use `return` — amdn, Mar 24 '14 at 08:35

Paolo · Accepted Answer · 2017-11-28T16:38:31.563

return from main() is equivalent to exit

the program terminates immediately execution with exit status set as the value passed to return or exit

return in an inner function (not main) will terminate immediately the execution of the specific function returning the given result to the calling function.

exit from anywhere on your code will terminate program execution immediately.

status 0 means the program succeeded.

status different from 0 means the program exited due to error or anomaly.

If you exit with a status different from 0 you're supposed to print an error message to stderr so instead of using printf better something like

if(errorOccurred) {
    fprintf(stderr, "meaningful message here\n");
    return -1;
}

note that (depending on the OS you're on) there are some conventions about return codes.

Google for "exit status codes" or similar and you'll find plenty of information on SO and elsewhere.

Worth mentioning that the OS itself may terminate your program with specific exit status codes if you attempt to do some invalid operations like reading memory you have no access to.

score 4 · Answer 2 · answered Sep 05 '18 at 10:09

To indicate execution status.

status 0 means the program succeeded.

status different from 0 means the program exited due to error or anomaly.

return n; from your main entry function will terminate your process and report to the parent process (the one that executed your process) the result of your process. 0 means SUCCESS. Other codes usually indicates a failure and its meaning.

score 3 · Answer 3 · answered Mar 24 '14 at 08:26

3

return n from your main entry function will terminate your process and report to the parent process (the one that executed your process) the result of your process. 0 means SUCCESS. Other codes usually indicates a failure and its meaning.

answered Mar 24 '14 at 08:26

giorashc

13,691
3
35
71

Is it the same to say "parent process" than "calling function"? – carloswm85 Aug 09 '18 at 13:27

score 2 · Answer 4 · edited May 23 '17 at 12:34

As explained here, in the context of main both return and exit do the same thing

Q: Why do we need to return or exit?

A: To indicate execution status.

In your example even if you didnt have return or exit statements the code would run fine (Assuming everything else is syntactically,etc-ally correct. Also, if (and it should be) main returns int you need that return 0 at the end).

But, after execution you don't have a way to find out if your code worked as expected. You can use the return code of the program (In *nix environments , using $?) which gives you the code (as set by exit or return) . Since you set these codes yourself you understand at which point the code reached before terminating.

You can write return 123 where 123 indicates success in the post execution checks.

Usually, in *nix environments 0 is taken as success and non-zero codes as failures.

Søren Debois · Answer 5 · 2014-03-24T08:28:21.500

1

return n from main is equivalent to exit(n).

The valid returned is the rest of your program. It's meaning is OS dependent. On unix, 0 means normal termination and non-zero indicates that so form of error forced your program to terminate without fulfilling its intended purpose.

It's unusual that your example returns 0 (normal termination) when it seems to have run out of memory.

edited Mar 24 '14 at 08:28

answered Mar 24 '14 at 08:22

Søren Debois

5,598
26
48

EmptyData · Answer 6 · 2017-11-18T17:49:43.203

return in function return execution back to caller and exit from function terminates the program.

in main function return 0 or exit(0) are same but if you write exit(0) in different function then you program will exit from that position.

returning different values like return 1 or return -1 means that program is returning error .

When exit(0) is used to exit from program, destructors for locally scoped non-static objects are not called. But destructors are called if return 0 is used.

Difference between return 1, return 0, return -1 and exit?

6 Answers6

Linked