------- Additional Comments From ncm-nospam at cantrip dot org 2005-04-30 02:11 ------- Just to add... if sgetn() loops reading until it gets n bytes, but underflow() accepts a pipe's short reads, then in_avail() will report the size of the short read. Then, istream::read_some() will rdbuf->sgetn(p,rdbuf->in_avail()), thus matching POSIX pipe semantics when attached to a pipe.
(For those who don't know: as long as whoever is writing the other end of the pipe writes no more than PIPE_BUF bytes into it, then POSIX requires that read() deliver the bytes on write boundaries. Thus, if you're writing structs, the reader will see half a struct. If you're writing short-enough lines, the reader will only ever see complete lines -- although you might see more than one. Watch out that PIPE_BUF is 4K or more on Linux, but only 512 bytes on BSD!) It's exciting to finally get this right. With a bit more work, I see now that we might be able to support nonblocking file descriptors, and maybe even zero-copy I/O, too! Thank you, Ralf. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21286
