read part of text in file

my program logic : user open the program daily, enter the amount spent, program will create / read and record the number, user closed the program, continue next day..

The challenge :
I set the total saving of user to a fixed amount. However if the program once closed, the program can't work, it will just deduct from the fixed amount, so i plan to read the latest saving (or you guys have better way?)

Let say I have this in a file

Code:

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Date        Amount spend    Saving left


11/23/11        -20.00USD    980.00USD

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How to read just only the "RM 980.00"? read the last few char of the file? or use seek? I'm a newbie..

You read the whole file, and you extract what you need.

If you want to 'edit' the file in some way, you read the whole file, make your changes in memory and then write the whole file (ideally to a new file, and then rename the old one to be a backup).

Text files do not support random access updates if the length of the file is going to change as a result.