Functions - C Interview Questions VI

Q. Is using exit() the same as using return?

No. The exit() function is used to exit your program and return control to the operating system. The return statement is used to return from a function and return control to the calling function. If you issue a return from themain() function, you are essentially returning control to the calling function, which is the operating system. In this case, the return statement and exit() function are similar. Here is an example of a program that uses the exit()function and return statement:

#include <stdio.h>
#include <stdlib.h>
int main(int, char**);
int do_processing(void);
int do_something_daring();
int main(int argc, char** argv)
{
     int ret_code;
     if (argc < 3)
     {
          printf("Wrong number of arguments used!\n");
          /* return 1 to the operating system */
          exit(1);
     }
     ret_code = do_processing();
     ...
     /* return 0 to the operating system */
     exit(0);
}
int do_processing(void)
{
     int rc;
     rc = do_something_daring();
     if (rc == ERROR)
     {
          printf("Something fishy is going on around here..."\n);
          /* return rc to the operating system */
          exit(rc);
     }
     /* return 0 to the calling function */
     return 0;
}

In the main() function, the program is exited if the argument count (argc) is less than 3. The statement exit(1);tells the program to exit and return the number 1 to the operating system. The operating system can then decide what to do based on the return value of the program. For instance, many DOS batch files check the environment variable named ERRORLEVEL for the return value of executable programs.