C problems

[T. William Wells]

In article <7511 at bsu-cs.bsu.edu> dhesi at bsu-cs.bsu.edu (Rahul Dhesi) writes:
: It seems like overkill, but not detecting a full device is a *very*
: common bug in C programs.  (However, a possible optimization is to call
: ferror() just once before the output stream is closed instead of
: testing the value from putc all the time.)

Not quite: if you are going to do this, call fflush and then ferror
and you still need to check the results of fclose.

The fflush is needed so that the final write occurs; the fclose to
deal with things like failing to update directory entries.

(I suppose that the fclose should return error on a failure to write
the final buffer, thus eliminating the need for any checks other than
on the fclose, but several stdio implementations I've seen don't.)

Even better is to determine some points in your program that don't
occur too frequently, say <5% of the frequency of character writes,
and call ferror there as well. That way you catch the error after only
a few "file system full" messages get printed on the console rather
than 600 billion. :-) Frequently, a good place for a text file is
after each newline is written.

The message printing, BTW, is a serious problem with some UNIX's: a
good way to bring those systems to their knees is to get the kernel to
generate an unending series of messages. What happens is that, since
kernel message writing for these systems is polled, while a message is
being written, nothing other than interrupts are processed.

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Bill                            { uunet | novavax } !twwells!bill