Output to a selected file C++ Visual Studio 2015

Question

I need to output text from a textBox into a text file selected in a Save File Dialog. My code is below. I also need to write out the address of the file.

  private: System::Void saveToolStripMenuItem1_Click(System::Object^  sender, 
     System::EventArgs^  e)
  {
     SaveFileDialog saveFile;
     ofstream ofs;
     saveFile.ShowDialog(); //returns a DialogResult value (DialogResult.OK)
     string str = marshal_as<string>(saveFile.FileName); //file name
     ofs.open(str);

     if (str != "") //if a file is selected
     {
        ofs << "TestMessage 1, 2" << endl;
        ofs << str; //Displays current file name
        ofs << conc->GetConc(str, txtDisplay) << endl;
        ofs << marshal_as<string>(conc->GetConc(str, txtDisplay)) << endl;
        ofs.close(); 
     }
     else
        MessageBox::Show("No file is selected for output.");
  }

So far I think what I've got is working. However I still need to be able to get output from the textbox. I've tried using something like the following, but it's not working. Note: this would go just before "ofs.close();"

    ofs << txtDisplay->ToString() << endl;

I'm thinking the problem is with my GetConc method. Below are the header and body for the method. Am I returning the wrong thing?

string GetConc(string stringEntry, TextBox ^ tb);//HEADER
string Concordance::GetConc(string stringEntry, TextBox ^ tb)//BODY
{
   string s = stringEntry + "   ";
   String ^s2 = gcnew String(s.c_str());
   // add stringEntry to display string + "   "
   // for
   // if found, add iter->second 
   int count = 0;
   map <string, vector<int>>::iterator iter;

   for (auto iter = m.cbegin(); iter != m.cend(); iter++)
   {
   string test = iter->first;
   if (test == stringEntry)
   {
      vector<int>::iterator i;
      for (auto i = iter->second.cbegin(); i != iter->second.cend(); i++)
      {
         s2 += *i;
         if (i + 1 != iter->second.cend())
            s2 += ",";
      }
   }
}
tb->Text += s2 + "\r" + "\n";
return s;
}