open a text file that in use by another process

[chaos75]

i have this code but it wont open the log file of a program thats running and using that log file how can i watch that log file and store it in a string when it changes?

int count;
 String^ sFileName;	
 String^ sLine;
		
	private: System::Void b1_Click(System::Object^  sender, System::EventArgs^  e) {
			count = 0;
				 ofd1->ShowDialog();
				 sFileName = ofd1->FileName;
				 filenamelbl->Text=sFileName;	// set the path to the file we are going to open
				 StreamReader^ din = File::OpenText(sFileName);

				while ((sLine = din->ReadLine()) != nullptr) {
         count++;
		 sLine = ("line {0}: {1}", count, sLine );
		 logtb->Text =logtb->Text  + sLine + "\r\n";
     }

			 }
			


	};
}