iterator default value [modified]

[liquid_]

How can I check whether an iterator was assigned a value or not? In other words, if I create an iterator with default constructor what value will it present which I could check against? It is not the trivial case such this:

list::iterator it; //what does it contains?

but this:

map::iterator> aci;
AClass *ptr=someinitializedaclassptr;
if(aci[ptr]==UNINITIALIZED_ITERATOR)
{
dosomething();
}

In above example issuing aci[ptr] creates already an entry in the map with default constructed value list::iterator if there isn't a key of value ptr.

modified on Friday, August 5, 2011 7:48 AM

[Stephen Hewitt]

Read this thread on (ahem) stackoverflow: http://stackoverflow.com/questions/3395180/what-is-an-iterators-default-value[^]

Steve

[liquid_]

Well, it is obvious it has no special value as int val;. The problem is how to check this. I'll try the below code:

#include "list"
#include "map"
#include "iostream"

using namespace std;

int main()
{
list::iterator it,itnull;
map::iterator> imap;

it = imap\[1\]; //map creates entry with key '1' and default constructed iterator
if(it==itnull) //checking with other default constructed iterator
    cout<<"it unitialized"<