difference between function declaration: func() and func(void)

koyi · 11-18-2005, 08:31 PM

What is the difference between these two function declarations in C?

1) void func1();
2) void func2(void);

In a book I am reading, it says that in the first case, the compiler doesn't check the argument list passed to func1(); whereas in the second case func2() is explicitly declared to take no arguments.

I understand what that means but in real life how can the first case be useful?

Thanks.

spooon · 11-18-2005, 10:04 PM

I don't think there is a difference.

vivekr · 11-19-2005, 01:15 AM

Quote:

Originally posted by koyi
the compiler doesn't check the argument list passed to func1()
Thanks.

Do u mean that call such as this wouldn't raise errors-

Code:

func1(x,y);

koyi · 11-19-2005, 09:54 AM

Alright I have tested it with this piece of simple source code.

Code:

#include <stdio.h>

int func1();
int func2(void);

int main(int argc, char **argv) {

        int a, b;

        a = func1(1, 1, 2);
        b = func2();

        printf("a = %d\tb = %d\n", a, b);

        return 0;

}

int func1(int a, int b) {
        return a + b;
}

int func2(void) {
        return 3;
}

And this compiles cleanly and ran with the output:

Code:

a = 2   b = 3

As you can see, in the declaration func1() is declared as just func1().
In main(), it is called with 3 arguments but in the definition of func1() it only needs two of them.
But no errors occur in both the compilation and execution.
Well, I don't think this is a bug in the compiler or what but I am just wondering how can this be useful in real life.

Btw, if you pass any arguments to func2() the an error will occur when you try to compile it.

tuxdev · 11-19-2005, 10:19 AM

The declaration funct1() is actually funct1(...). main and printf are also declared that way as well. Specificly, the declarations are main(...) and printf(char *format,...). funct1(void) forces no arguments, as your book says.