How to erase the last byte in a text file?

Dev Shed Forums Sponsor:

February 10th, 2004, 06:02 PM

therobman

Junior Member

Join Date: Jan 2004

Posts: 4

Time spent in forums: < 1 sec
Reputation Power: 0

How to erase the last byte in a text file?

Hello,

I have a c++ program that needs to output data to a text file on command. This I can do, however I end up with an extra line in my file consisting of just a newline character, which I need to delete.

I know how to use seekp() to put the file pointer at this character, how can I then erase it? Effectively write backwards to the file?

February 10th, 2004, 06:17 PM

jubitzu

Contributing User

Join Date: Jan 2004

Location: Colorful Colorado

Posts: 743

Time spent in forums: 21 h 16 m 10 sec
Warnings Level: 10
Number of bans: 1
Reputation Power: 0

the solution would be to fix your original program such that it does not print the extra new line.

February 10th, 2004, 07:04 PM

M.Hirsch

Contributing User

Dev Shed God 1st Plane (5500 - 5999 posts)

Join Date: Oct 2000

Location: Back in the real world.

Posts: 5,966

Time spent in forums: 1 Month 2 Days 52 m 24 sec
Reputation Power: 189

You are programming on windows?
Set the file mode to "binary" to avoid the trailing newline.

I am not sure if windows has this function too, but I have found this in my man pages:

Code:

#include <unistd.h>

     int
     truncate(const char *path, off_t length);

     int
     ftruncate(int fd, off_t length);

hth,
M.

__________________
--
Manuel Hirsch - Linux, FreeBSD, programming, administration articles, tutorials and more.

February 10th, 2004, 07:17 PM

therobman

Junior Member

Join Date: Jan 2004

Posts: 4

Time spent in forums: < 1 sec
Reputation Power: 0

I threw your library header in but it looks like Windows doesn't have that one.

I also don't think that binary mode would be an option either.

Thanks for the replies though!

February 10th, 2004, 07:33 PM

Ancient Dragon

Contributing User

Join Date: Jan 2004

Location: near St. Louis Illinois

Posts: 3,288

Time spent in forums: 1 Week 2 Days 20 h 37 m 22 sec
Reputation Power: 23

Win32 api function SetEndOfFile() will truncate a file to the current file pointer position. See MSDN for description and parameters.

But as someone else said, you will be better off fixing your program.

February 10th, 2004, 07:33 PM

M.Hirsch

Contributing User

Join Date: Oct 2000

Location: Back in the real world.

Posts: 5,966

Time spent in forums: 1 Month 2 Days 52 m 24 sec
Reputation Power: 189

Hmmm. Did your compiler come with a help file, specifically the "Platform SDK" Documentation? If not, you should definitively get it!

It's not ftruncate() but SetEndOfFile() - I found it here:
http://msdn.microsoft.com/library/d...etendoffile.asp

hth,
M.

[edit]
Hey Ancient Dragon, you beat me by a few seconds

How to erase the last byte in a text file?

Developer Shed Advertisers and Affiliates