getpt — open the pseudoterminal master (PTM)
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <stdlib.h>
| int
            getpt( | void); | 
getpt() opens a
      pseudoterminal master and returns its file descriptor. It is
      equivalent to
    open(/dev/ptmx, O_RDWR | O_NOCTTY);
      on Linux systems, though the pseudoterminal master is located elsewhere on some systems that use GNU Libc.