#include <stdio.h> char *ctermid(char *s);
char *ctermid_r(char *s);
The ctermid() function generates the path name of the controlling terminal for the current process and stores it in a string.
If s is a null pointer, the string is stored in an internal static area whose address is returned and whose contents are overwritten at the next call to ctermid(). Otherwise, s is assumed to point to a character array of at least L_ctermid elements. The path name is placed in this array and the value of s is returned. The constant L_ctermid is defined in the header <stdio.h>.
The ctermid_r() function behaves as ctermid() except that if s is a null pointer, the function returns NULL.
The difference between ctermid() and ttyname(3C) is that ttyname() must be passed a file descriptor and returns the actual name of the terminal associated with that file descriptor, while ctermid() returns a string (/dev/tty) that will refer to the terminal if used as a file name. The ttyname() function is useful only if the process already has at least one file open to a terminal.
The ctermid() function is unsafe in multithreaded applications. The ctermid_r() function is MT-Safe and should be used instead.
When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should be used only with multithreaded applications.
See attributes(5) for descriptions of the following attributes: