Is main with parameter list of void different from main with an empty parameter list?

Question

Possible Duplicate:
Why is the type of the main function in C and c++ left to the user to define?

What is a void ? Anyone provide some examples, proper use of void ? And what is the difference when we write void main (void) or main() ?

Answer 1

In C, in general, (void) means no arguments required in function call, while () means unspecified number of arguments.

e.g.

void foo(void)
{
   // body
}

void bar()
{
    //body
}

In calling enviroment,

foo();  // Correct 
foo(1); // Incorrect
bar();  // Correct
bar(1); // Also correct

This was the general explanation.

But for your case for main() , C99 Standard says that,

5.1.2.2.1 Program startup

The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters: int main(void) { /* ... */ }

or

with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared): int main(int argc, char *argv[]) { /* ... */ } or equivalent;

or

in some other implementation-defined manner.

So, in this void main(void) return type should be int.

And at last , for main(), return type is not given so implicitly return type would be int.

Answer 2

Excluding the return type of the main as in

main(){
}

doesn't mean that it's a void type, it depends on the compiler. I think it can be said it's generically interpreted as

int main(){
}

The void type tells the compiler that there is no 'entity' (no 'storage'), so

void func(int i)

takes an int but returns nothing. In the case of parameters this:

void func()

is equivalent to this:

void func(void)

which indicates more explicitly that it does not take parameters. Different story is with the type void * which is a type, a pointer to something dimensionless.

Answer 3

Basically, void is a data type, which basically used with method declaration. It means nothing or no type. Eg:

1) int myFunc(void) -- the function takes nothing.

2) void myFunc(int) -- the function returns nothing

3) void* data; -- 'data' is a pointer to data of unknown type, and cannot be dereferenced

Answer 4

Void means "emptyness". In your example of void main() it means that the functions main() does not return a value. I feel obliged tell you that void main() should be avoided (no pun intended) at all costs, use int main() instead. int main() makes sure your program can return a value of type int to the OS on close. There are numerous other uses of void, check out this website if you want to read more about this.

Answer 5

void is a data type with no values. It is also an incomplete data type that cannot be completed. When used as a return type for a function, it indicates that the function does not return a value:

void foo(int x);

When used as a parameter list, it indicates that the function takes no arguments:

void bar(void);

This is different from an empty parameter list, which indicates that the function takes an unspecified number of arguments (in C; in C++, an empty parameter list is the same as using void):

void bletch();

No object (variable) can be typed void. However, you can declare pointers of type void *: these are "generic" pointers, and can be converted to and from other pointer types without an explicit cast. The standard memory allocation functions malloc, calloc, and realloc all return void *:

double *darr = malloc(sizeof *darr * rows);

In a hosted implementation (basically, anything with an operating system), main must be declared as

int main(void)

or

int main(int argc, char **argv) // the parameter names can be whatever you want,
                                // but argc and argv are the usual convention;
                                // char **argv is equivalent to char *argv[]

or in some other implementation-defined manner; an implementation may accept

void main()

as a legitimate signature for main, but it must explicitly document that somewhere.