CODEWITHSUNDEEP
c++stlset
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Reputation: 7788

How to iterate over a STL set and selectively remove elements?

The following code does not work correctly. How should it be done correctly?

for (std::set<Color>::iterator i = myColorContainer.begin();
            i!=myColorContainer.end();
            ++i)
{
    if ( *i  == Yellow)
    {
        DoSomeProccessing( *i );
        myColorContainer.erase(i);
    }
}

Upvotes: 7

Views: 11869

Answers (3)

Viktor Sehr
Viktor Sehr

Reputation: 13099

You don't need a loop as youre dealing with a set.

std::set<Color>::iterator it = myColorContainer.find(Yellow);
if (it != it.myColorContainer.end()){
  DoSomeProcessing(*it);
  myColorContainer.erase(it);
}

Upvotes: 6

Artyom
Artyom

Reputation: 31233

for (std::set<Color>::iterator i = myColorContainer.begin();
            i!=myColorContainer.end(); /* No i++ */)
{
    if ( *i  == Yellow)
    {
        DoSomeProccessing( *i );
        std::set<Color>::iterator tmp = i;
        ++i;
        myColorContainer.erase(tmp);
    }
    else {
        ++i;
    }
}

Once you go to next message with ++i it is guaranteed to be valid - property of std::set that iterators on inserted elements are never invalidated unless the element is removed.

So now you can safely erase previous entry.

Upvotes: 2

Adrian Regan
Adrian Regan

Reputation: 2250

Try:

for(std::set<Color>::iterator it = myColorContainer.begin(); 
    it != myColorContainer.end();) { // note missing it++
     if( (*it) == Yellow ) {
        DoSomeProcessing(*it);
        myColorContainer.erase(it++); // post increment (original sent to erase)
     }
     else {
       ++it; // more efficient than it++;
     }
}

Upvotes: 7

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