Reasons as to why fread would fail

Here is a piece of code :

Code:

if ((t = (fread(buffer,BLOCK_SIZ,1,diskp))) != 1)  // Read from disk to buffer
{
	if(feof(diskp) != 0)
	{
		fprintf(stdout,"End of file reached. %d Blocks read.\n",f);
		return t;
	}
	
	if((err_num = ferror(diskp)) != 0)
	{
		fprintf(stderr,"%s\n",strerror(err_num));
	}

	fprintf(stderr,"Error in disk read : Buffer write failed. %d\n",f);
	return 0;
}

Here's my problem. Often, I'm calling this piece of code to read a block of data from a file pointed to by diskp. Now on certain occasions (namely, when diskp is opened with "r+b" permission), fread fails (and reads 0 elements) and it therefore gets into the if statement. Furthermore, everytime it fails it always outputs "Error in disk read : Buffer write failed". This is where I'm confused. How can my program get so far ? From what I grasp from fread's man page, it should fail if it reaches EOF or gets an error (in which case ERRNO is set). But I believe I've testing both of these, but neither of these conditions corresponding to what my program is telling me. So how come fread is failing ? Is there some other, "alternate" method for fread to fail or something ?

Thanks in advance.

http://c-faq.com/stdio/fupdate.html ?

> Is there some other, "alternate" method for fread to fail or something ?
Yes.

> if ((t = (fread(buffer,BLOCK_SIZ,1,diskp))) != 1)
If say your file is 120 bytes long, and BLOCK_SIZ is say 100 then the first fread will read a 100 byte block and return 1.
The next fread will not find a "complete" 100 byte block, so won't read any of it (feof() remains false), and fread will return 0.

So assuming you're in the context of a binary file, if you seek to a location bytes-1, then call fread to read a block of size bytes, instead of reading the bytes-1, and then signlaing EOF, it won't read anything and return 0 ?

Do you have any idea of the reason it was implemented in such a fashion ? I know I don't quite see why they'd do it that way...

fread() was intended for reading data structures (and other fixed-size entities) from files. If there isn't enough data in the file to form one structure, it makes sense to fail the read.