We create Fstream1 which opens the file and stores the start of file. Now we copy the fstream1 to fstream2.
Note: fstream1 will read file upwards whereas fstream2 will read file downwards.
Before reading a chunk of data upwards or downwards the respective fstream* has to remember the initial start position.
Problem is when we read the position of both the fstream’s is moving leading to loss of the position intended to store.
Example: Consider initial fstream1.pos = 500 & fstream2.pos =500. Now if I read upwards 200 characters the fstream1.pos=300 but fstream2.pos should remain 500, in our case the fstream2.pos also becomes 300.
Similarly if I read downwards.
fileStream1 = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite, 1, true);
fileStream2 = filestream1; // want this but without opening the file again
considering filestream would be like filepointers in C++.
Note: above task is in C#.
Assuming that you would scan upwards or downwards on a file to locate a position int he file faster, I would suggest: -
1) Open the file once.
2) Keep two variables - UpPointer & DownPointer and initial them as UpPointer = DownPointer = 500 (from your example).
3) When a read or scan is made, update the respective pointer.