#include <stdlib.h> int unlockpt(int fildes);
The unlockpt() function unlocks the slave pseudo-terminal device associated with the master to which fildes refers.
Portable applications must call unlockpt() before opening the slave side of a pseudo-terminal device.
Upon successful completion, unlockpt() returns 0. Otherwise, it returns −1 and sets errno to indicate the error.
The unlockpt() function may fail if:
The fildes argument is not a file descriptor open for writing.
The fildes argument is not associated with a master pseudo-terminal device.
See attributes(5) for descriptions of the following attributes: