C++ STL Vector Iterator accessing members of an Object

Question

I think I've declared a Vector with an object correctly. But, I don't know how to access it's members when looping with Iterator.

In my code, the line --->> cout << " " << *Iter;

How do I print the contents of the members? Like *Iter.m_PackLine ???

Not sure if I used the correct terminology, but appreciate the help! Thanks

class CFileInfo
{
  public:
      std::string m_PackLine;
      std::string m_FileDateTime;
      int m_NumDownloads;
};

void main()
{
  CFileInfo packInfo;

  vector<CFileInfo, CFileInfo&> unsortedFiles;
  vector<CFileInfo, CFileInfo&>::iterator Iter;

  packInfo.m_PackLine = "Sample Line 1";
  packInfo.m_FileDateTime = "06/22/2008 04:34";
  packInfo.m_NumDownloads = 0;
  unsortedFiles.push_back(packInfo);

  packInfo.m_PackLine = "Sample Line 2";
  packInfo.m_FileDateTime = "12/05/2007 14:54";
  packInfo.m_NumDownloads = 1;
  unsortedFiles.push_back(packInfo);

 for (Iter = unsortedFiles.begin(); Iter != unsortedFiles.end(); Iter++ )
 {
    cout << " " << *Iter; // !!! THIS IS WHERE I GET STUMPED
    // How do I output values of the object members? 
 }
}  // end main

Answer 1

cout << " " << *Iter;

will only work if CFileInfo has an overloaded operator<< that can output your struct. You can output individual members of the struct instead like this:

cout << " " << Iter->m_PackLine;

Alternatively, the following is equivalent to that:

cout << " " << (*Iter).m_PackLine;

You have to put parentheses around *Iter, since the member-access operator binds thighter otherwise.

On a side-node, make your main function return int instead of void. making it return void is not valid in C++.

---

You declare the vector like this:

vector<CFileInfo, CFileInfo&> unsortedFiles;

The second argument to vector should be another thing. It's not needed for your code to give the vector a second argument at all. Just use this:

vector<CFileInfo> unsortedFiles;

---

Another thing i noticed is you increment the iterator using Iter++ (called postfix increment). For iterators, always prefer ++Iter, which is called prefix increment.

Answer 2

Use (*iter).member or iter->member.

You can also use temporaries:

CFileInfo &fileInfo = *iter;
cout << " " << fileInfo.myMember;

Also, for what you're doing, you'd probably want a const_iterator instead of an (mutable) iterator.

In addition, std::vector is a template accepting a typename and an allocator, not two typenames. You can use the default allocator by stripping the second template argument:

vector<CFileInfo> unsortedFiles;
vector<CFileInfo>::iterator Iter;

---

Some nit-picking:

• main should return an int.
• It'd probably be best to declare your iterator variable in the for statement.
• It'd probably be faster in run-time performance to use the prefix ++ operator (++iter) instead of the postfix operator (iter++) in your for loop.
• No need for your comment about main() ending.