Wrong returned value in main function?

Question

I previously read that 0 in C-Language refers to false while 1 is true. And have noticed that the main function returns 0 but why is that? in case all of my code ran successfully it should return true (1). Another related question, I still can't understand who can use the returnable value? since no other function called the main function inside my program so nothing can know if my program ran well or not. I am a little bit confused.

Answer 1

Your logic would make sense if the return value of main were interpreted as a Boolean value, but it isn't. Returning from the initial call to main is like calling the exit function: It reports a termination status to the system you're running on.

Standard C specifies 3 portable exit statuses:

• 0, indicating success
• EXIT_SUCCESS, also indicating success
• EXIT_FAILURE, indicating failure

(The last two are macros defined in <stdlib.h>.)

On Unix, any 8-bit value (0 .. 255) is allowed. All non-zero values are interpreted as error codes. There is no universal convention for what any given number means, just that 0 represents success and anything else some kind of failure.

As for who can use the return value: On Unix, a parent process can use wait or waitpid to get the exit status of a terminated child.

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In the C standard library, functions that perform an action generally don't return a true/false status. (Tests such as islower or isdigit do, but they don't have any other effects.) For example, remove (which deletes a file) returns 0 on success and -1 on error. This is also a common pattern with Unix system calls. For exmple, open returns a file descriptor (a non-negative integer) on success and -1 on error.

Answer 2

It's essentially what @Brandon already said in the comments.

main is supposed to return the exit/error code of the program. In the Unix convention, 0 is used to indicate no error (the error value is "false"). And then positive values are used for indicating that there is an error and what error it was.