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From: euamts@eua.ericsson.se (Mats Henricson)
Newsgroups: comp.lang.c++
Subject: Re: Help needed in c++
Message-ID: <1991Jun19.132158.8495@eua.ericsson.se>
Date: 19 Jun 91 13:21:58 GMT
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marina@cs.hw.ac.uk (Marina Georgiadou) writes:


>I'm currently working in Borland C++, and I have encountered
>the following construct in one of Borland's examples :

>class A{
>// ...
>public :
>	virtual int f() const;
>//...
>};

>Does anybody know the meaning of this const postfix ??

Well, I suppose you have got 600 replys allready, but who knows:

The const postfix means that the function f() may not change any of the
data members of the class A. This is a very neat feature since you know
that this function is safe for the data in the object of type A. It has
however yet another meaning: if you have a constant object of type A:
	const A a;
Now you can only use the member functions of A that are declared const.
This is rather natural; since a is declared const it cannot be changed,
and hence only safe functions that does not change the inner state of a
should be possible to call.

If you were using g++, i.e. GNU:s version of C++, this const postfix
would have yet another meaning, since the GNU compiler does not allow
const functions to change ANYTHING, i.e. not even global constants. You
are using Borland C++ and it should not put this restraint on const
declared functions. So just forget you heard about it ;-)

Mats Henricson, Sweden