Is there any reason (other than syntactic ones) that you'd want to use
FILE *fdopen(int fd, const char *mode);
or
FILE *fopen(const char *path, const char *mode);
instead of
int open(const char *pathname, int flags, mode_t mode);
when using C in a Linux environment?
First, there is no particularly good reason to use fdopen
if fopen
is an option and open
is the other possible choice. You shouldn't have used open
to open the file in the first place if you want a FILE *
. So including fdopen
in that list is incorrect and confusing because it isn't very much like the others. I will now proceed to ignore it because the important distinction here is between a C standard FILE *
and an OS-specific file descriptor.
There are four main reasons to use fopen
instead of open
.
fopen
provides you with buffering IO that may turn out to be a lot faster than what you're doing with open
.fopen
does line ending translation if the file is not opened in binary mode, which can be very helpful if your program is ever ported to a non-Unix environment (though the world appears to be converging on LF-only (except IETF text-based networking protocols like SMTP and HTTP and such)).FILE *
gives you the ability to use fscanf
and other stdio functions.open
function.In my opinion the line ending translation more often gets in your way than helps you, and the parsing of fscanf
is so weak that you inevitably end up tossing it out in favor of something more useful.
And most platforms that support C have an open
function.
That leaves the buffering question. In places where you are mainly reading or writing a file sequentially, the buffering support is really helpful and a big speed improvement. But it can lead to some interesting problems in which data does not end up in the file when you expect it to be there. You have to remember to fclose
or fflush
at the appropriate times.
If you're doing seeks (aka fsetpos
or fseek
the second of which is slightly trickier to use in a standards compliant way), the usefulness of buffering quickly goes down.
Of course, my bias is that I tend to work with sockets a whole lot, and there the fact that you really want to be doing non-blocking IO (which FILE *
totally fails to support in any reasonable way) with no buffering at all and often have complex parsing requirements really color my perceptions.