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#include <stdio.h> char *ctermid (s) char *s;
ctermid() generates the pathname 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, the contents of which are overwritten at the next call to ctermid(), and the address of which is returned. 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 <stdio.h> header file.
ctermid() returns a pointer to a null string if it fails, or if the pathname that would refer to the controlling terminal cannot be determined.
The difference between ctermid() and ttyname.3v 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. Thus ttyname() is useful only if the process already has at least one file open to a terminal. ctermid() is useful largely for making code portable to (non-UNIX) systems where the current terminal is referred to by a name other than /dev/tty.
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