Hi, I've read the definitions of EOF and feof() in C language, but still not understanding very well what are the differences of using them?
the both are expressing "reaching end of the file!
Can anyone please explain the differences between using those both commands? if possible with examples would be more sufficient.
thanks!
And why it's wrong to writein c(p is a pointer to a file)?Code:while(!feof( fp ))
Well, EOF is a number. feof() is a function.
Also as for why using feof() to control a loop is wrong, read: FAQ > Why it's bad to use feof() to control a loop - Cprogramming.com
I'm with you.Originally Posted by whiteflags
but is there a logically difference between writing
andCode:char c; while (c !=EOF )
? the both are indicating to a condition that simplify "whenever we didn't reach the end of the file, continue with the iterations of the while loop .."Code:while (!feof(fp)) /*fp is a pointer to a file*/
Yes, and you would know the difference if you bothered to read the page that I linked.but is there a logically difference between writing:
Most of the time, when you compare against EOF, it is because you are doing it in a larger expression checking the return value of a function like fgetc(). fgetc() will return EOF if it fails. One time it can fail is if all of the file has been read, so there is no more content. Now, consider feof(), which is usually used incorrectly. It shouldn't be used to control a loop, because it depends on another function like fgetc() to fail first, and change the stream state; if that doesn't happen, then feof() will lead to unwanted results.
Consider this:
The above is fine because when end of file is reached, fgetc will return EOF, hence terminating the loop before something is done with c. Notice that c is an int because EOF is an int.Code:int c; while ((c = fgetc(fp)) != EOF) { /* do something with c */ }
Now, consider:
The above is problematic because when end of file is reached, fgetc will return EOF, but something will be done with c, even though it is EOF, before the loop terminates, i.e., the check happens in a wrong place.Code:int c = 0; while (c != EOF) { c = fgetc(fp); /* do something with c */ }
Likewise, consider:
The above has the exact same problem as the previous example. So, the problem is not with feof per se: the problem is with how it is used to control the loop, i.e., the apparently obvious way to use it to control a loop is wrong.Code:int c; while (!feof(fp)) { c = fgetc(fp); /* do something with c */ }
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