How to iterate over this list of pointers in c++?

Question

I have a list of pair s with CString s and want to iterate over it and use first and second elements of each pair in the list inside the for loop, but I have a problem with doing that. Can someone explain to me why this doesn't work and help me with the solution?

This is my code:

list<pair<CString, CString>*> listSubstStr;
for (std::list<pair<CString, CString>*>::iterator it = listSubstStr.begin(); it != listSubstStr.end(); ++it) {
      CxXML* p = pRoot->AddTag(NOWKT("Pair"));
      p->SetString("First", it->first);
      p->SetString("Second", it->second);
   }

Here are the errors:

Answer 1

It seems you mean

  p->SetString("First", ( *it )->first);
  p->SetString("Second", ( *it )->second);

That is the expression *it has the type pair<CString, CString>* .

Also check whether this code is called within a constant member function. If so then you have to use const_iterator instead of iterator.

Answer 2

Look at your types.

You're iterating over a list<pair<CString, CString>*> , so the elements are pair<CString, CString>* .
That means that *it is also a pointer, so you need to dereference twice:

(*it)->first

or use the modern range loop:

for (auto element: listSubstStr)
{
      CxXML* p = pRoot->AddTag(NOWKT("Pair"));
      p->SetString("First", element->first);
      p->SetString("Second", element->second);
}

(The use of std::list and of pointers to pairs are both questionable, by the way. The more common choice would be vector<pair<CString, CString>> .)

Answer 3

You have a list<pair<CString, CString>*> ie a list of pointers to pair<CString,Cstring> .

Dereferencing an iterator will get you a pair<CString, CString>*& . Hence to get the pair you need to dereference the iterator, then the pointer: (*it)->first .

It is rather likely that you didnt need pointers in the first place.