c++/10364: compile error using vector, comma operator and for loop

[Phil Edwards]

The following reply was made to PR c++/10364; it has been noted by GNATS.

From: Phil Edwards <phil@jaj.com>
To: pdemarco@ppg.com
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c++/10364: compile error using vector, comma operator and for loop
Date: Wed, 9 Apr 2003 16:10:52 -0400

 On Wed, Apr 09, 2003 at 07:34:56PM -0000, pdemarco@ppg.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