1CTERMID(3P) POSIX Programmer's Manual CTERMID(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 ctermid — generate a pathname for the controlling terminal
13
15 #include <stdio.h>
16 char *ctermid(char *s);
18
20 The ctermid() function shall generate a string that, when used as a
21 pathname, refers to the current controlling terminal for the current
22 process. If ctermid() returns a pathname, access to the file is not
23 guaranteed.
24 The ctermid() function need not be thread-safe if called with a NULL
26 parameter.
27
29 If s is a null pointer, the string shall be generated in an area that
30 may be static, the address of which shall be returned. The application
31 shall not modify the string returned. The returned pointer might be
32 invalidated or the string content might be overwritten by a subsequent
33 call to ctermid(). The returned pointer might also be invalidated if
34 the calling thread is terminated. If s is not a null pointer, s is
35 assumed to point to a character array of at least L_ctermid bytes; the
36 string is placed in this array and the value of s shall be returned.
37 The symbolic constant L_ctermid is defined in <stdio.h>, and shall have
38 a value greater than 0.
39 The ctermid() function shall return an empty string if the pathname
41 that would refer to the controlling terminal cannot be determined, or
42 if the function is unsuccessful.
43
45 No errors are defined.
46 The following sections are informative.
48
50 Determining the Controlling Terminal for the Current Process
51 The following example returns a pointer to a string that identifies the
52 controlling terminal for the current process. The pathname for the ter‐
53 minal is stored in the array pointed to by the ptr argument, which has
54 a size of L_ctermid bytes, as indicated by the term argument.
55 #include <stdio.h>
58 ...
59 char term[L_ctermid];
60 char *ptr;
61 ptr = ctermid(term);
63
65 The difference between ctermid() and ttyname() is that ttyname() must
66 be handed a file descriptor and return a path of the terminal associ‐
67 ated with that file descriptor, while ctermid() returns a string (such
68 as "/dev/tty") that refers to the current controlling terminal if used
69 as a pathname.
70
72 L_ctermid must be defined appropriately for a given implementation and
73 must be greater than zero so that array declarations using it are
74 accepted by the compiler. The value includes the terminating null byte.
75 Conforming applications that use multiple threads cannot call ctermid()
77 with NULL as the parameter. If s is not NULL, the ctermid() function
78 generates a string that, when used as a pathname, refers to the current
79 controlling terminal for the current process. If s is NULL, the return
80 value of ctermid() is undefined.
81 There is no additional burden on the programmer—changing to use a hypo‐
83 thetical thread-safe version of ctermid() along with allocating a buf‐
84 fer is more of a burden than merely allocating a buffer. Application
85 code should not assume that the returned string is short, as some
86 implementations have more than two pathname components before reaching
87 a logical device name.
88
90 None.
91
93 ttyname()
94 The Base Definitions volume of POSIX.1‐2017, <stdio.h>
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98 Portions of this text are reprinted and reproduced in electronic form
99 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
100 table Operating System Interface (POSIX), The Open Group Base Specifi‐
101 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
102 Electrical and Electronics Engineers, Inc and The Open Group. In the
103 event of any discrepancy between this version and the original IEEE and
104 The Open Group Standard, the original IEEE and The Open Group Standard
105 is the referee document. The original Standard can be obtained online
106 at http://www.opengroup.org/unix/online.html .
107 Any typographical or formatting errors that appear in this page are
109 most likely to have been introduced during the conversion of the source
110 files to man page format. To report such errors, see https://www.ker‐
111 nel.org/doc/man-pages/reporting_bugs.html .
112IEEE/The Open Group 2017 CTERMID(3P)