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fwrite problem

Posted on 1997-03-21
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Last Modified: 2012-05-04
Though a Windows program, for compatibility reasons and a greater simplicity with pointers, I am using fwrite to write to files with VC 4.2, with all patches. The problem I am having is that I am getting a corrupt file when writing to it. What happens is that I read the file, do an fseek to specific offset and write to that position. This works fine in all other cases, except that I seem to be writing more than I have indicated with this line of code:

       fwrite (&buffer, sizeof(char), 3, prt);

Once again, I have an fseek just before this (which is working ok) and then write the contents of the buffer. So I shouldn't have a corrupt file problem. I used fopen with r+b, so read-write binary files. That's ok.

I've tried everything possible to solve the problem, but no luck; it's still corrupt! Your suggestions will be greatly appreciated!

Roger
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Question by:RJV
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Accepted Solution

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syed_dgreat earned 210 total points
ID: 1162184
You should have mentioned in greater detail by what you mean
by corrupted file.? Is it unreadable or is the content just plain garbage.?
BTW, I notice someting not quite right (not really sure though).
The line
fwrite (&buffer, sizeof(char), 3, prt);
suggests to me that buffer is not a string (probably an int or
non-pointer variable).
if it's a string, it should be like this:-
fwrite(buffer, ....);
or if it's integer,
fwrite(&buffer, sizeof(int), ...);
This is probably the bug!! If that's so, it probably the one causes the corrupted file.
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Author Comment

by:RJV
ID: 1162185
Indeed, my example is wrong, though the & character is ignored. More characters seem to be written to the file, which is text but opened as binary due to extended characters (above 128 decimal, or 7fh. I have to go the a part of the text file and change some control characters there, but more than those characters are changed. This despite the fact that writing is limited to 3 characters. I haven't managed to find the problem. At this stage I'll try other ways to access the file, particularly as this has never happened before!
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