[c] Difference between return 1, return 0, return -1 and exit?

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.

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.

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.

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.

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.

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.