feof() in C file handling

Question

I am reading a binary file byte-by-byte,i need determine that whether or not eof has reached.

feof() doesn't works as "eof is set only when a read request for non-existent byte is made". So, I can have my custom check_eof like:

if ( fread(&byte,sizeof(byte),1,fp) != 1) {
    if(feof(fp))
    return true;
}
return false;

But the problem is, in case when eof is not reached, my file pointer is moved a byte ahead. So a solution might be to use ftell() and then fseek() to get it to correct position.

Another solution might be to buffer the byte ahead in some temporary storage.

Any better solutions?

Answer 1

I'm not clear, but if you're interested in knowing before you read the byte if EOF has been reached, put your feof() test before the fread() rather than after it.
actually, if I read correctly, you don't even want to do the fread so:

return feof(fp) ? true : false;

Answer 2

I would suggest using:

fseek(myFile, 0, SEEK_END);
fileLen = ftell(myFile);
fseek(myfile, 0, SEEK_SET);

When you first open the file to determine the length. Then set up your read-loop to never read off the end. You can use ftell to figure out where you are, and compare to fileLen to figure out how much further you have to go.

Answer 3

I typically do something like this:

int get_next_char(FILE* fp, char *ch)
{
    return fread(ch, sizeof(char),1, fp) == 1;
}

// main loop
char ch;
while (get_next_char(fp, &ch))
    process_char(ch);

if (!feof(fp))
    handle_unexpected_input_error(fp);

Answer 4

If you're reading a byte at a time, the idiomatic way to do this is with fgetc:

int c;
while ((c = fgetc(fp)) != EOF) {
   // Do something.
}

and then you shouldn't need to deal with feof.

Answer 5

It's best to structure your code so that you try to read some data and if the read does not succeed due to reaching the end-of-file, you deal with it there (i.e. see Kristopher Johnson's answer).

If you absolutely hate this, you can use ungetc to return a single character back to the stream and it will be available in the next read call:

int c = fgetc(fp);
if (c == EOF)
{
    // handle eof / error
}
else
{
    ungetc(c, fp);

    // the next read call is guaranteed to return at least one byte

}