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SOCKATMARK(3) BSD Library Functions Manual SOCKATMARK(3) NAME sockatmark -- determine whether the read pointer is at the OOB mark LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <sys/socket.h> int sockatmark(int s); DESCRIPTION To find out if the read pointer is currently pointing at the mark in the data stream, the sockatmark() function is provided. If sockatmark() re- turns 1, the next read will return data after the mark. Otherwise (as- suming out of band data has arrived), the next read will provide data sent by the client prior to transmission of the out of band signal. The routine used in the remote login process to flush output on receipt of an interrupt or quit signal is shown below. It reads the normal data up to the mark (to discard it), then reads the out-of-band byte. #include <sys/socket.h> ... oob() { int out = FWRITE, mark; char waste[BUFSIZ]; /* flush local terminal output */ ioctl(1, TIOCFLUSH, (char *)&out); for (;;) { if ((mark = sockatmark(rem)) < 0) { perror("sockatmark"); break; } if (mark) break; (void) read(rem, waste, sizeof (waste)); } if (recv(rem, &mark, 1, MSG_OOB) < 0) { perror("recv"); ... } ... } RETURN VALUES Upon successful completion, the sockatmark() function returns the value 1 if the read pointer is pointing at the OOB mark, 0 if it is not. Other- wise the value -1 is returned and the global variable errno is set to in- dicate the error. ERRORS The sockatmark() call fails if: [EBADF] The s argument is not a valid descriptor. [ENOTTY] The s argument is a descriptor for a file, not a socket. SEE ALSO recv(2), send(2) HISTORY The sockatmark() function was introduced by IEEE Std 1003.1-2001 ("POSIX.1"), to standardize the historical SIOCATMARK ioctl(2). The ENOTTY error instead of the usual ENOTSOCK is to match the historical be- havior of SIOCATMARK. BSD October 13, 2002 BSD
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY
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