TITLE: Where to put default argument values


PROBLEM: mharriso@digi.lonestar.org (Mark Harrison)

When a member function has an initialized parameter, should
the initialization go in the class declaration (in the header file)
or in the function declaration? 
  ...
file X.h
 
class X {
    void f(int n = 0);	<------- here?
};
 
file X.c

X::f(int n = 0)	        <------- or here? (It's an error to do it twice)
{
    // ...
}


RESPONSE: gs4t@virginia.edu (Gnanasekaran Swaminathan), 16 Jan 93

It depends on how you want to use it.

Say for example, if you want all the users of class X
to use the default value, then give the default value
int the function declaration in class X. 

#include <X.h>

X a;
a.f (); // ok.

If on the other hand, you want the users to specify the
value and only you, the class designer, want to use
the default value, then give the default value in the
function definition (in X.c) and write all other functions 
that will be making a call to the function and use the
default value after the function definition.

#include <X.h>

X a;
a.f (); // error. no function X::f ().


// X.cc

void X::f (int n=0)
{...}

void X::g ()
{
  f (); // ok. use the default value
}