Re: iterator error

From:

bnonaj <n2xssvv.g02gfr12930@ntlworld.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 06 Apr 2007 10:49:25 GMT

Message-ID:

<VApRh.4374$nM6.4124@newsfe2-win.ntli.net>

James Kanze wrote:

On Apr 6, 3:02 am, "Victor Bazarov" <v.Abaza...@comAcast.net> wrote:

?????????? wrote:

windows xp, visual studio 2005
----------------------------------------------------------------------------------------------------------------------------------
#include <iostream>
#include <map>
using namespace std;
int main()
{
map<int, int>::iterator it = 0;
if( it != 0 ) //break point,
this is an run time error?
cout<<"ok!";
}
----------------------------------------------------------------------------------------------------------------------------------
why it can be assign "0", but can't compare with "0"?

The iterator type in 'map' is implementation-defined. What
it means to initialise it with (int)0 is implementation-defined.
Why operator != (int)0 doesn't work is (you guessed it!)
implementation-defined.

It's not even implementation-defined, it's undefined.

Strictly speaking without an implementation it wouldn't even exist and
therefore would not compile

Most good implementations will not compile either of the above
lines.

You need to either look at the code
in the debugger to see what's going on or ask in the newsgroup
dedicated to your implementation (microsoft.public.vc.* family
of newsgroups come to mind).

Actually, he needs to change his code. It might help if he
explained what he is trying to accomplish.

--
James Kanze (Gabi Software) email: james.kanze@gmail.com
Conseils en informatique orient?e objet/
Beratung in objektorientierter Datenverarbeitung
9 place S?mard, 78210 St.-Cyr-l'?cole, France, +33 (0)1 30 23 00 34

I agree the code is somewhat dodgy and probably not portable

JB