Question

I have stumbled across a problem where I am attempting to read in a file, which is, according to windows, ‘87.1 kb’ in size, and using the ftell method in program, returns ‘89282’, effectively confirming what windows is saying.

So why is every method to read chars from the file only returning 173 or 174 characters?

The file is a .GIF file renamed to .txt (and I am trying to build a program that can load the data fully as I am working on a program to download online images and need to run comparisons on them).

So far I have tried:

• fgetc – This returns 173/174 chars.
• fread – Same as above, this is with a string with 1024 or more spaces available.
• fgets – Doesn’t work (as it doesn’t return how many characters it has read – characters which include nulls).
• setvbuf – Disabling this with _IONBF, or even supplying a buffer of 1024 or more only means 173/174 is still returned.
• fflush – This produced a ‘result’, although a negative one – it returned ‘2’ chars instead of ‘173’.

I am utterly stumped as to why it isn’t reading anything more than 173/174 chars. Is there something I need to compensate for or expect at the lower level? Some buffer I need to expand or some weird character I need to look out for?

Answer 1

Here’s one thing to look at. Have a look at the file in a hex viewer and see if there’s a CTRL-Z somewhere around that 173/174 offset.

Then check to see if you’re opening it with the "r" mode.

If so, it may be that the Windows translation between text and binary is stopping your reading there because CTRL-Z is an EOF marker in text mode. If so, you can probably fix this with "rb" mode on the fopen.

Failing that, you need to post the smallest code segment that exhibits the problem behaviour. It may be obvious to some of us here but only usually if we can see the code 🙂