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From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: comp.lang.c++
Subject: Re: const
Message-ID: <137@tdatirv.UUCP>
Date: 29 Aug 90 15:22:45 GMT
References: <5027@atexnet.UUCP>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Organization: Teradata Corp., Irvine
Lines: 35

[I tried to mail this, but it bounced, so here it is]

In article <5027@atexnet.UUCP> you write:
>I have a question about the use of const in member functions. It seems to me taht there are three different uses for const in member functions. They are:
>
>1) constant arguments to the function A::f(const x)
>2) constant return type from the function const char* A::g()
>3) constant function where the object or 'this' is a constant.
>
>The second and third types seems to confuse me. Are there really two distinct
>types, and what is the syntax.

Yes, and in fact #3 is more closely related to #1 than #2 (since the object
is passed as hidden extra argument in most implementations).

Case #2 is used where the function returns some private data that should not
be modified by the caller.

Case #3 is used where the member function should not be allowed to modify the
state of the object it is invoked on.
>
>I have seen 
>
>int A::f() const; in some code as well as int const A::f(); and I am not sure
>if there is a diference. The former syntax does not seem to be accepted by g++.

	You seem to have an old version of g++.  The former syntax is new to
cfront version 2.0, and its equivalents from other vendors. (The latest g++
does in fact accept it, I believe).

int A::f() const;   declares a 'constant function' where 'this' is constant.
int const A::f();   is the same as:
const int A::f();   and declares a function returning a constant result,
		    which is only meaningful if the function returns a pointer
		    or a reference.