Eric Blake writes: >> What's really happening is that we need to peek at the first few bytes >> of f before deciding which program to call in popen. After peeking, >> there's a call to fseek(f,0,0) before the popen, with the intention that >> the child receives a file pointer set to the beginning of the file. (I >> left this out of my STC because it didn't affect the outcome.) This >> apparently works on Linux. > > Corinna is correct - you need to fflush() after the fseek() for it to > affect the underlying offset. Or, just use read()/lseek() instead of > fread()/fseek() in the parent, to avoid stdio buffering altogether. > That way, you'll guarantee the offset the child process will inherit > without having to worry about flushing buffered state.
Basically this is the same category of bug that was in rcs for a while. It isn't easy to find out what is and isn't guaranteed about these things across a fork and since things work slightly differently on Linux that's something you can probably expect to show up more often. Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ Samples for the Waldorf Blofeld: http://Synth.Stromeko.net/Downloads.html#BlofeldSamplesExtra -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
