What is the meaning of having void in the constructor definition?

Question

Given the following code:

#pragma once

class B
{
public:

    B(void)
    {
    }

    ~B(void)
    {
    }
};

I know I can also write this:

#pragma once

class B
{
public:

    B()
    {
    }

    ~B()
    {
    }
};

What is the purpose of having void in the 1st example? Is it some type of practise that states the constructor takes ZERO parameters?

TIA

Andrew

Answer 1

afaik if you pass void into the constructor or any function as the argument it means that the function dosnt take any argument so example a and b are equal. but i am not sure if any of them change the function signature in any way or make it run faster etc.

Answer 2

The two are same, at least in C++. In C, providing an empty pair of parentheses typically means an unspecified parameter list (as opposed to an empty parameter list). C++ does not have this problem.

How can a correct answer get downvoted so many times? Yet another SO bug?

Answer 3

A long time ago you did something like this in C (my pre-ISO C is rusty :-)

void foo(a, b) int a, int b { }

while C++ was being created the name mangling required the types of the arguments, so for C++ it was changed to:

void foo(int a, int b) { }

and this change was brought forward to C.

At this point, I believe to avoid breaking existing C code this:

void foo()

and this:

void foo(void)

meant two very different things, () means do not check for the argument number or type, and (void) means takes no arguments. For C++ () meaning not to check anything was not going to work so () and (void) mean the same thing in C++.

So, for C++ () and (void) were always the same thing.

At least that is how I remember it... :-)

Answer 4

While for all practical purposes as a user of C++, the accepted answer is good enough, it's not entirely correct. Read for example this email thread discussing the difference: http://www.archivum.info/comp.std.c++/2006-04/msg00202.html

Answer 5

I just wanted to add that when you use void after the parameters like function():void it is used to indicate that the function does not return a value.