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RE: c++/10364: compile error using vector, comma operator and for loop
- From: "DeMarco, Paul" <pdemarco at ppg dot com>
- To: nobody at gcc dot gnu dot org
- Cc: gcc-prs at gcc dot gnu dot org,
- Date: 9 Apr 2003 20:36:00 -0000
- Subject: RE: c++/10364: compile error using vector, comma operator and for loop
- Reply-to: "DeMarco, Paul" <pdemarco at ppg dot com>
The following reply was made to PR c++/10364; it has been noted by GNATS.
From: "DeMarco, Paul" <pdemarco at ppg dot com>
To: 'Phil Edwards' <phil at jaj dot com>
Cc: gcc-gnats at gcc dot gnu dot org
Subject: RE: c++/10364: compile error using vector, comma operator and for
loop
Date: Wed, 9 Apr 2003 16:28:55 -0400
Shamed.
I mis-copied the bites.begin() as bites.begin
:(
-----Original Message-----
From: Phil Edwards [mailto:phil at jaj dot com]
Sent: Wednesday, April 09, 2003 4:11 PM
To: DeMarco, Paul
Cc: gcc-gnats at gcc dot gnu dot org
Subject: Re: c++/10364: compile error using vector, comma operator and
for loop
On Wed, Apr 09, 2003 at 07:34:56PM -0000, pdemarco at ppg dot com wrote:
> Here is a strange little bug where the addition of a comma operator kills the compile. Below it works with 2 ints.
> Regards.
> --Paul
>
You didn't include the error messages you received. Here's my guess:
> std::vector<string>::iterator oCMIter;
> std::vector<string> bites;
>
> for ( int iI = 3, oCMIter = bites.begin();
> oCMIter != bites.end();
> oCMIter++, iI++ )
> {
> cout << "hello" << endl;
> }
Buggy code. The 'init' statement in a for loop can only be a simple
declaration or an expression.
"int iI = 3, oCMIter = bites.begin();" declares two integers, one
called iI (initialized to 3) and another called oCMIter, initialized to
bites.begin(). But there's no conversion from an iterator (the return
value from bites.begin()) to an integer (the oCMIter being defined and
initialized), so you get an error.
The std::vector<string>::iterator oCMIter outside the for loop is shadowed
by the int oCMIter inside the loop. You would get a shadowing warning,
/if/ it were legal code.
Move the iI declaration out of the for-init-statement. That way it becomes
an expression instead of a declaration:
std::vector<string>::iterator oCMIter;
std::vector<string> bites;
int iI;
for ( iI = 3, oCMIter = bites.begin(); ...
Phil
--
To err is human; to forgive is simply not our policy.
- MIT Assassination Club