Message-ID: <c=US%a=_%p=Hassler_Communic%l=DAISY-970522160439Z-148@daisy.hcst.com>
From: Bryan Murphy <bryan DOT murphy AT HCST DOT com>
To: "'Stefano Brozzi'" <brozzis AT mag00 DOT cedi DOT unipr DOT it>
Cc: "'djgpp AT delorie DOT com'" <djgpp AT delorie DOT com>
Subject: RE: C++ problem
Date: Thu, 22 May 1997 12:04:39 -0400
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>> >in C++ is possible to have default arguments to member functions
>> >(i.e. int foo( int bar = 3 ) {...} ) .
>> >Could I have, as default value, the value of a member variable ?
>> >(i.e. something like:
>> >
>> >struct Question {
>> >   int zoo;
>> >   Question() : zoo(3) {}       // this makes evrybody happy ;)
>> >   int foo( int bar = Question::zoo );
>> >}
>> >
>> 
>> Question:  Why not just make
>> 
>>         int foo(int bar=3);
>> 
>> the default?  It does the exact same thing as this snipet of code you've
>> shown us.  Am I missing something here?  Your method might work if
>> you make zoo static, but I'm still not even sure of it or it's need.
>
>I want zoo to be a variable. In this example I assigned 3 to zoo
>to avoid a : "Ehi, you are handling uninit. vars" answer.
>
>And if I declare it static:
>s.cc:5: field `int Question::zoo' is static; only point of
>initialization is its declaration
>where line 5 is  Question() : zoo(3) {}  

Ok, I think I understand.  You want Zoo to point to some default value
that can change.  I think you probably want this, keep in mind two
things,
first you can only declare default values for static variables outside
of the
class (at least I think that is true) and I changed this from a struct
to a
class.  I compiled this, and it compiles fine.  g++ can't find the g++
library
for some reason, so I couldn't run it, but it should work.

Also, since zoo is static, it is common to all classes.  If you don't
want
that, I think you are out of luck.  g++ won't compile that saying zoo
must
be static.  I suspect this is because if zoo was variable, the function
would
never know which value to look at in which class.  I don't see why this
is
a problem, but then again the C++ standards comittee hasn't really
accomplished much the last few years, so who knows why.

#include "iostream.h"

class MyClass
{
private:
        static int zoo;

public:
        MyClass()
        {
                cout << "Wee!  I do nothing!!" << endl;
        }

        SetDefaultValue(int x)
        {
                zoo = x;
        };

        int Foo(int val = MyClass::zoo)
        {
                cout << val << endl;
        };

};

int MyClass::zoo = 3;

int main()
{
        MyClass temp;

        temp.Foo();
        temp.SetDefaultValue(5);
        temp.Foo();
        temp.Foo(3);
};