return value from main

i recently found out that it should be only int main() and not void main() as per standards.
also,i found out that the return value is 0 in case of a normal termination.
but what is the use of this return value?where can it be used?

now don't gun me down as usual :tongue: im just a beginner.

The shell calling the program receives the return value. In Windows console, for example, this value is retrieved through the ERRORLEVEL environment variable. In the BASH shell, it's the $? environment variable.

In typical bash scripts the variable $? (as mentioned above) is checked after important commands.
The script continues if it is 0 (or depending upon the program, something else) and handles the errors if it denotes an error.

I'm pretty sure the C standard does not specify which value (e.g. 0) is for success. I think that's up to the OS/environment, but *nix systems generally use 0 for success. The standard does however define two macros, EXIT_FAILURE and EXIT_SUCCESS that are safe and portable, and probably your best bet. Another thing to note, main is always specified as returning int, but the OS/environment may interpret that as signed or unsigned, and as a char, short or int. E.g.

Code:

---

$ cat foo.c
int main(void)
{
    return -1;
}
$ gcc -Wall foo.c -o foo
$ ./foo
$ echo $?
255

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Linux interprets the return code as a signed char. Not sure what windows does.

0 is always success as well.
Even on those systems (such as VMS) where "success" is a non-zero value.

However, if you return something else (other than 0 or the two constants), then you will need to check how your environment interprets specific return values.

Quote:

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Originally Posted by theju112

i recently found out that it should be only int main() and not void main() as per standards.
also,i found out that the return value is 0 in case of a normal termination.
but what is the use of this return value?where can it be used?

now don't gun me down as usual :tongue: im just a beginner.

---

Actually the minimum C program is..

Code:

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int main (void)
  {

    // your code here

    return ErrorCode; }  // typically this is 0

---

The returned value in windows can be used by batch files (IF ERRORLEVEL) or by other programs (In the case of CreateProcess()) to judge the sucess or failure of a program. A program that returns a non-0 value might well be considered to have failed.

Now for the "shooting you down part"... In your first thread, you were told this at least half a dozen times and roundly ignored it.

Quote:

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Originally Posted by anduril462

Another thing to note, main is always specified as returning int, but the OS/environment may interpret that as signed or unsigned, and as a char, short or int. ... Linux interprets the return code as a signed char. Not sure what windows does.

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unsigned int ... so that programs can report windows error codes when returning.

Quote:

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Originally Posted by manasij7479

The script continues if it is 0 (or depending upon the program, something else) and handles the errors if it denotes an error.

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this is the exact answer i needed.
any other value apart from 0 would indicate an error. so the return value is used for error handling.

Quote:

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Originally Posted by theju112

this is the exact answer i needed.
so any other value apart from 0 would indicate an error. the OS(shell) can now try to solve this error.

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If you return any value other than 0 or EXIT_SUCCESS, that would indicate an error. Note: The actual value returned to the OS is implementation defined.

Quote:

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Originally Posted by AndrewHunter

If you return any value other than 0 or EXIT_SUCCESS, that would indicate an error. Note: The actual value returned to the OS is implementation defined.

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Also note that many return values may not constitue errors... One example is in batch files, where the ERRORLEVEL keyword contains the return value from the process... You might use 0 to continue along, 10 to branch to a different place in the script, 123 might take you some where else...
A great many programs return values that are not, strictly speaking, errors.

Another example is a child program hatched with CreateProcess()... it's return value can be used to signal it's parent what to do next using GetExitCodeProcess() in a switch statement... In that case you can have hundreds of possiblities...

The only true error returned to the OS is EXIT_FAILURE.