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Basically i am having problems with my code - this is homework so would rather not post it in here for obvious reasons. If it becomes truely important for me to do so then i will have to as i am so stuck.

i am reading 2 text files and it also has a separator , these values come from the command line, just assume that the separator in this case is xx

File a
a
b
c


File b
d
e

Output should be
axxd
bxxe
cxx

the problem is that my code just doesn't do the last line correctly

i get an output of 

axxd
bxxe

I hope you guys can gather what i am doing wrong without me posting all my code, but my logic works on this principle;

while not at the end of the file for files a and b
    get a line using fgets from a
    create a character pointer and set it to the first occurrence of \n in the line using strchr
    if the pointer isn't null
        set the pointers value to be the end of line

get the line from b as above
and now write the line from a, the separator and the line from b to file
Cœur
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Biscuit128
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    show a minimal sample of the C code you're having the problem with – Eli Bendersky Mar 06 '10 at 13:14
  • Almsot impossible, due to the fact its only 8 lines of code :S – Biscuit128 Mar 06 '10 at 13:18
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    You are reluctant to post 8 lines of code? Something using while() and fgets() is a matter of top security? – Tim Post Mar 06 '10 at 13:21
  • You seem to have removed the code. Was this intentional as it makes answers to this question _non sequitor_? – CB Bailey Mar 06 '10 at 14:32
  • its because i wanted advice on how to fix a problem, which everyone has kindly provided. The thing is that i didn't really want to post code as on submission it "looks" like i am cheating even if i really am only seeking opinions... . I think its fair to say i openly admitted it was homework yet some gave provided attempted full solutions which seem similar to my original code.... – Biscuit128 Mar 06 '10 at 14:39

2 Answers2

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This is your first logic problem: while(!feof(a) && !feof(b))

This means that if either file has reached the end then you stop processing, even if there are more lines in the other file.

CB Bailey
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  • thanks, that gives me soemthign to work off of, however the first means you have found more :S !! – Biscuit128 Mar 06 '10 at 13:41
  • Good old EOF flag. They should put in the documentation "NEVER USE THIS FUNCTION FOR TESTING WHETHER YOU CAN READ MORE", then maybe people would stay away from it. – Tronic Mar 06 '10 at 13:42
  • Well, if you just change the while condition and leave the code as it stands you will be attempting to call `fgets` on streams that are potentially at `EOF`. You need to check the return value of `fgets` to make sure that you don't treat old buffer contents as newly read data. – CB Bailey Mar 06 '10 at 13:46
  • logically end of file would suggest there was nothing else left to read :D – Biscuit128 Mar 06 '10 at 13:46
  • The EOF flag is only guaranteed to be set _after_ a failed read. This is why `feof` is considered a code smell. In almost all cases code is much more robust if the result of the particular read function that is tested. In many instances of code that use `feof`, the function isn't called at the correct point in the code and often there is no corresponding `ferror` check. – CB Bailey Mar 06 '10 at 13:54
  • Strange enough, it can also get set after a successful read that simply happens to peek past the end. – Tronic Mar 06 '10 at 16:12
  • @Tronic: Yes, on many platforms this happens for things like `fscanf` where it might be reading, say, digits for a number. It hits the end, sets `EOF` but it still read a good number. `feof` doesn't tell you whether it worked; you need to check the return value of `fscanf`. I didn't emphasise all the reasons that `feof` is usually not the right function in my last comment. – CB Bailey Mar 06 '10 at 16:57
  • DONT use `feof()`: http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong – chqrlie Feb 05 '17 at 14:07
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Maybe you don't print a newline after printing the last line? Then it may not display on your screen at all. Notice that fgets only puts a newline in your buffer if the original line had one and the last line of a file might not.

Tronic
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