Thread: Parameter and return value specifics

Originally Posted by Zaff

1.) Is there any difference between a funtion with no parameters that does not include anything between the parenthesis and one that only includes the data type void? In other words, any difference between "int main ()" and "int main (void)"? I've experimented with both and observed no difference.

not in today's versions... but I think... now don't quote me on this cause I wasn't around for this, but I think some of the original versions had a different meaning for the empty parameter list.

Originally Posted by Zaff

2.) Is there any difference between an integer main function that returns 0 and a void main function? I noticed that most reputable C books teach the reader to declare main as an integer returning function but many tutorials also just use void ("void main (void) and void main()"). Likewise, I've experimented with this in the compiler as well and observed no difference.

the difference is that void main is non-standard.

>In other words, any difference between "int main ()" and "int main (void)"?
It depends on where you use it. For a function declaration, there's a subtle and disturbing difference:

Code:

void foo(); // Takes an unknown number and type of parameters
void foo ( void ); // Takes no parameters

For a function definition, there's still a minor difference:

Code:

// Does not ensure a complete prototype
void foo()
{
}

// Ensures a complete prototype
void foo ( void )
{
}

A full prototype, of course, guarantees that you'll be informed of improper use of the function. You should always use void when you intend for a function to have no arguments, and you should refrain from using empty parameter lists because it's a feature of the language that's being phased out with new revisions of the standard. It's also dangerous.

>Is there any difference between an integer main function that returns 0 and a void main function?
Yes, main returning an integer is correct and main returning anything else is not. The C standard makes it very clear that the following declarations of main (and anything directly equivalent) are allowed:

Code:

int main ( void );
int main ( int argc, char *argv[] );

Anything else is implementation-specific. It could either work if your implementation allows it, or invoke undefined behavior. That kind of uncertainty makes using void main exceptionally stupid.