Re: iterator error

From:

"Jim Langston" <tazmaster@rocketmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 5 Apr 2007 21:14:23 -0700

Message-ID:

<MOjRh.6083$nu5.1728@newsfe02.lga>

"??????????" <chendong.jy@gmail.com> wrote in message
news:1175821161.252561.56780@b75g2000hsg.googlegroups.com...

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"?

Read the other's comments. You are trying to compare an iterator and an
integer. On some (most?) implementations it = 0 would probably be invalid
also. The correct usage is to initialize them with .begin() or .rbegin() or
some iterator value. For example:

int main()
{
   std::map<int, int> MyMap;
   std::map<int, int>::iterator it = MyMap.begin();
   // code
}

persontally, I normally use iterators mostly in for loops to iterate through
a container (vector or map) or to get a pointer to a newly inserted member.
Such as:

typedef std::map<int, int> IntMap;
IntMap MyMap;
// fill MyMap
for ( IntMap::iterator it = MyMap.begin(); it != MyMap.end(); ++it )
   std::cout << it->first << "-" << it->second << "\n";