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* Re: c++/3760: g++ rejects legal code
@ 2001-07-21 12:26 Julian v. Bock
0 siblings, 0 replies; 3+ messages in thread
From: Julian v. Bock @ 2001-07-21 12:26 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
The following reply was made to PR c++/3760; it has been noted by GNATS.
From: julian@OpenIT.DE (Julian v. Bock)
To: "Uwe F. Mayer" <mayer@tux.org>
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c++/3760: g++ rejects legal code
Date: 21 Jul 2001 21:22:42 +0200
Hi
>>>>> "Uwe" =3D=3D Uwe F Mayer <mayer@tux.org> writes:
Uwe> c++ rejects to compile a member function changing a mutable
Uwe> data member of a constant object instance. Direct changes of
Uwe> the mutable member (if public) are fine.
>> How-To-Repeat:
Uwe> Compile the program bug8.cc included below, and you will get
Uwe> the compile-time error message: $ g++ bug8.cc bug8.cc: In
Uwe> function `int main()': bug8.cc:19: passing `const class_m' as
Uwe> `this' argument of `void class_m::incr_i()' discards
Uwe> qualifiers
This is not a compiler bug.
The compiler complains because you are trying to call a non-const
member function of a const object. ("passing `const class_m' as `this'
argument of `void class_m::incr_i()' discards qualifiers").
Make class_m::incr_i a const member function and you are fine.
Julian
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OpenIT GmbH Tel +49 211 239 577-0
Julian v. Bock Fax +49 211 239 577-10
Jahnstr. 18 julian@openit.de
40215 D=FCsseldorf http://www.openit.de
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: c++/3760: g++ rejects legal code
@ 2001-07-21 13:02 nathan
0 siblings, 0 replies; 3+ messages in thread
From: nathan @ 2001-07-21 13:02 UTC (permalink / raw)
To: gcc-bugs, gcc-prs, mayer, nobody
Synopsis: g++ rejects legal code
State-Changed-From-To: open->closed
State-Changed-By: nathan
State-Changed-When: Sat Jul 21 13:02:12 2001
State-Changed-Why:
Not a bug. you misunderstand mutable.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=3760&database=gcc
^ permalink raw reply [flat|nested] 3+ messages in thread
* c++/3760: g++ rejects legal code
@ 2001-07-21 11:46 Uwe F. Mayer
0 siblings, 0 replies; 3+ messages in thread
From: Uwe F. Mayer @ 2001-07-21 11:46 UTC (permalink / raw)
To: gcc-gnats
>Number: 3760
>Category: c++
>Synopsis: g++ rejects legal code
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: rejects-legal
>Submitter-Id: net
>Arrival-Date: Sat Jul 21 11:46:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator: Uwe F. Mayer
>Release: 3.0
>Organization:
tux.org
>Environment:
System: Linux tosca 2.2.18 #2 Thu Mar 8 13:48:25 PST 2001 i686 unknown
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../gcc-3.0/configure --disable-nls --prefix=/usr/local/gcc-3.0
>Description:
c++ rejects to compile a member function changing a mutable data member of
a constant object instance. Direct changes of the mutable member (if public)
are fine.
>How-To-Repeat:
Compile the program bug8.cc included below, and you will get the compile-time
error message:
$ g++ bug8.cc
bug8.cc: In function `int main()':
bug8.cc:19: passing `const class_m' as `this' argument of `void
class_m::incr_i()' discards qualifiers
The program bug8.cc:
====================
#include <iostream>
using namespace std;
class class_m {
public:
class_m() : i(0) {}
void incr_i() {i++;}
void print() const {cout << i << endl;}
mutable int i;
};
int main() {
const class_m obj_m;
obj_m.print();
obj_m.i++; // works
obj_m.print();
const_cast<class_m*>(&obj_m)->incr_i(); // works
obj_m.print();
obj_m.incr_i(); // rejected at compile time
obj_m.print();
}
>Fix:
Work-around: if function() is a mutator member function changing a mutable data
member of a constant object instance, use instead of:
obj_m.function()
the expression:
const_cast<class_m*>(&obj_m)->function()
>Release-Note:
>Audit-Trail:
>Unformatted:
^ permalink raw reply [flat|nested] 3+ messages in thread
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2001-07-21 12:26 c++/3760: g++ rejects legal code Julian v. Bock
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2001-07-21 13:02 nathan
2001-07-21 11:46 Uwe F. Mayer
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