I would like to use low level read()s to read a file that is
constantly growing. It appear that when I hit what was the end of
the file at the time that I opened it, I get an error 22 “Invalid
Argument” regardless of how big the file is when I get to that point.
Is there a way to continuously read the file like the ‘tail -f’
utility without having to:
int where;
where = tell();
close()
open()
lseek( where );
/* some operands have been omited to protect the innocent */
Bill Caroselli <qtps@earthlink.net> wrote:
I would like to use low level read()s to read a file that is
constantly growing. It appear that when I hit what was the end of
the file at the time that I opened it, I get an error 22 “Invalid
Argument” regardless of how big the file is when I get to that point.
Just as a guess, when you hit the EINVAL, try:
lseek(fd, 0, SEEK_CUR);
then try read() again.
(I looked at tail -f, it’s implemented using stdio functions.)
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Bill Caroselli <qtps@earthlink.net> wrote:
I would like to use low level read()s to read a file that is
constantly growing. It appear that when I hit what was the end of
the file at the time that I opened it, I get an error 22 “Invalid
Argument” regardless of how big the file is when I get to that point.
A disk filesystem will not behave that way. You should get a final
read() which returns 0 at EOF; after more data has been written to
that file the next read will return it (without you having to do
anything or close/open the file again). What filesystem are you using
that misbehaves like this (EINVAL)? Or are you sure you don’t have
a bug in your calling of lseek() - it would return EINVAL if you have
mixed up the argument order?
Is there a way to continuously read the file like the ‘tail -f’
You can sleep() after a read() returns 0 and loop and retry …
… works for me in a quick test (no seeking needed either).