Why add void to method parameter list

Question

I've seen methods with the following signature:

void foo (void); 

They take no argument, however I'm wondering whether doing this is useful or not. Is there a reason why you would want to do it?

Answer 1

This is a holdover from older versions of C, where foo() meant "a function with an unknown number of parameters" and foo(void) means "a function with zero parameters." In C++, foo() and foo(void) both mean "a function with zero parameters", but some people prefer the second form because it is more explicit.

Answer 2

The C++03 standard says (emphasis mine):

8.3.5.2

The parameter-declaration-clause determines the arguments that can be specified, and their processing, when the function is called. [Note: the parameter-declaration-clause is used to convert the arguments specified on the function call; see 5.2.2. ] If the parameter-declaration-clause is empty, the function takes no arguments.

This means that if you are talking to the compiler it's just a matter of taste.

If you are writing code that will be read by others, then the C++ way of doing things is

void foo(); 

The other form remains valid only for reasons of compatibility with C, where there was a difference among the two signatures.