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Help with file management. Please help!!

Tom
OK I'm trying to go to the end of a file and delete the contents
upwards until I meet a certain character. How can I do this? (NOTE:
I'm using text files)
Jul 19 '05 #1
2 2904
If you don't mind brute force you can do:

farthest_pos = 0
open file
while not eof
read char
if it is target char
farthest_pos = current_pos
wend
rewind
copy from 0 to farthest_pos to temp file
close file
remove file
rename temp file to original file
"Tom" <sn***@hotmail.com> wrote in message
news:78**************************@posting.google.c om...
OK I'm trying to go to the end of a file and delete the contents
upwards until I meet a certain character. How can I do this? (NOTE:
I'm using text files)

Jul 19 '05 #2
Tom wrote:
OK I'm trying to go to the end of a file and delete the contents
upwards until I meet a certain character. How can I do this? (NOTE:
I'm using text files)


This is very painful (at least to most operating systems). From
reading articles in news:comp.lang.c and news:comp.lang.c++, there
is no constant or standard method to position a file to a offset
measured in units of characters. With this knowledge, backspacing
through a file character by character is not portable. A case in
point is "\r\n": is it one or two characters?

Another rule about files that is hindering your activitiy is that
files don't shrink. You really can't "delete" a character in the
middle or end without creating a new file. The standard idiom
for delete sections in a file is to copy all the "wanted" stuff
to a new file and delete the old file.

Given the above points, a likely process is to read the entire
file into a container, then seach the container. A stack seems
very appropriate. This algorithm could be modified by searching
the file for the given character and saving the file positions.
After the file is processed, rewind it and copy everything up
to the last position saved to a new file. Two passes of reading
the file are required; but less memory is consumed. This latter
technique is portable since you are saving the position of a file
which is generated by the OS and not modifying.

--
Thomas Matthews

C++ newsgroup welcome message:
http://www.slack.net/~shiva/welcome.txt
C++ Faq: http://www.parashift.com/c++-faq-lite
C Faq: http://www.eskimo.com/~scs/c-faq/top.html
alt.comp.lang.learn.c-c++ faq:
http://www.raos.demon.uk/acllc-c++/faq.html
Other sites:
http://www.josuttis.com -- C++ STL Library book
http://www.sgi.com/tech/stl -- Standard Template Library

Jul 19 '05 #3

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