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Re: freopen/fread/popen bug

On 2/27/2015 11:20 AM, A L wrote:
I think that would create an unacceptable performance penalty for the child process.

The child process would not be affected at all!  FILE* will be
unbuffered only in your
application, yet "cat" will read from a file descriptor "1" (and may
or may not apply any
buffering on top of it, such as FILE*, on its own).  Since you are
going to read only a few
bytes out of "f" and leave the rest to "cat" (per your example), there
is no performance
penalty;  in fact there will be some gain not to pre-fill a buffer for
"f" (which you don't need

Also, you can just use basic unix IO (read() vs. fread()), and call
prior to popen().  This way, there's no user-level buffering and file
position is consistent with
your actions and expectations.

Thanks (and thanks to Corinna and Eric) for correcting my misconceptions. We have several viable solutions now, and I'm working with the upstream maintainers to decide which one to use.


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