Stripping <items in here> from a text file

what i wan to do is get rid of items in <items in here>
for example, for the string "dsafgsgwrgh<itema>grsgwrhhwr<itemb>fsdf"

i want to get rid of "itema" and "itemb"
here is my code
- open file
- copy file to a CString
- look for <
- look for >

Code:
 	CString file_string;
	CString file_string_temp;
	int start_index;
	int end_index;
	f.Read(file_string.GetBuffer(f.GetLength()),f.GetLength());

	start_index = file_string.Find("<");
	end_index = file_string.Find(">");
	file_string_temp = file_string.Left(start_index);

	int aaa = file_string.GetLength();
	int b=5;
but unfortunately it doesnt work
is the file too big? the file is about 2,000,000,000 in f.GetLength
file_string.Left(start_index); copies the entire file_string instead of only copying left strings

can somebody tell me what's wrong?