?
Solved

Write to file 5 bytes before EOF

Posted on 2004-08-17
8
Medium Priority
?
453 Views
Last Modified: 2010-04-15
_file = fopen("../src/bleh.lst", "a+");
      char buf[256];
                fseek(_file, -4, SEEK_END);
      fprintf(_file, buf);
      fclose(_file);


Long story short, it works fine but I need it to append to the file in a different initial position..
Someone help me out?
0
Comment
Question by:BangorCC
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 2
  • 2
8 Comments
 
LVL 86

Assisted Solution

by:jkr
jkr earned 700 total points
ID: 11822593
That should be more like

 _file = fopen("../src/bleh.lst", "a+");
    char buf[256];
               fseek(_file, 5, SEEK_END);
    fprintf(_file, buf);
    fclose(_file);

Alternatively, you could

struct stat st;

stat("../src/bleh.lst", &st);

_file = fopen("../src/bleh.lst", "a+");
    char buf[256];
               fseek(_file, st.st_size - 5, SEEK_SET);
    fprintf(_file, buf);
    fclose(_file);
0
 
LVL 22

Accepted Solution

by:
grg99 earned 300 total points
ID: 11822753
???

I don't see anywhere where anything is put into "buf".

I don't see where you check that "_file" did receive a valid file ptr.

What if the file is less than 4 chars long?  Does the right thing happen?

The info one gets from stat() is always out of date.  Using its info to seek on a growing file isnt going to work well every time.

Using fprintf() in this fashion is mighty dangerous... What if buf happens to contain some %-sign format directives?

0
 
LVL 86

Expert Comment

by:jkr
ID: 11822981
>>The info one gets from stat() is always out of date.  

Interesting. I wonder why that isn't regarded a bigger problem than Y2k....
0
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

Author Comment

by:BangorCC
ID: 11823911
Like I said, it works fine
I figured out my problem, here's your points, have a nice day
0
 

Author Comment

by:BangorCC
ID: 11823929
+a argument _always_ starts at the end of a file when you write to it... solution is to open in +r mode, and fseek, SEEK_END it :-) Thanks though.
0
 
LVL 86

Expert Comment

by:jkr
ID: 11824005
May I ask why you *accept* a comment as an answer  which does not address your question at all but maily states some unrelated (and partially incorrect) information?
0
 
LVL 22

Expert Comment

by:grg99
ID: 11825293
Which part is partially incorrect?   :)

{  stat() can only tell you what the stats *were*, not what they are right now. )



0
 
LVL 86

Expert Comment

by:jkr
ID: 11825417
If you use 'stat()' before you open the file to wite 5 bytes before the end, the information will be accurate. That's what I suggested. However, I'll take that back since I apparently missed the "growing file" part :o)

Oh, and the "unrelated part" also, since the remark addressing 'fprintf()' is a good point.

Sorry about being a bit hasty *g*
0

Featured Post

VIDEO: THE CONCERTO CLOUD FOR HEALTHCARE

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Have you thought about creating an iPhone application (app), but didn't even know where to get started? Here's how: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Important pre-programming comments: I’ve never tri…
Examines three attack vectors, specifically, the different types of malware used in malicious attacks, web application attacks, and finally, network based attacks.  Concludes by examining the means of securing and protecting critical systems and inf…
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use nested-loops in the C programming language.
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use while-loops in the C programming language.
Suggested Courses

762 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question