1FTOK(3P) POSIX Programmer's Manual FTOK(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 ftok - generate an IPC key
13
15 #include <sys/ipc.h>
16 key_t ftok(const char *path, int id);
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21 The ftok() function shall return a key based on path and id that is
22 usable in subsequent calls to msgget(), semget(), and shmget(). The
23 application shall ensure that the path argument is the pathname of an
24 existing file that the process is able to stat().
25 The ftok() function shall return the same key value for all paths that
27 name the same file, when called with the same id value, and return dif‐
28 ferent key values when called with different id values or with paths
29 that name different files existing on the same file system at the same
30 time. It is unspecified whether ftok() shall return the same key value
31 when called again after the file named by path is removed and recreated
32 with the same name.
33 Only the low-order 8-bits of id are significant. The behavior of ftok()
35 is unspecified if these bits are 0.
36
38 Upon successful completion, ftok() shall return a key. Otherwise,
39 ftok() shall return (key_t)-1 and set errno to indicate the error.
40
42 The ftok() function shall fail if:
43 EACCES Search permission is denied for a component of the path prefix.
45 ELOOP A loop exists in symbolic links encountered during resolution of
47 the path argument.
48 ENAMETOOLONG
50 The length of the path argument exceeds {PATH_MAX} or a pathname
51 component is longer than {NAME_MAX}.
52 ENOENT A component of path does not name an existing file or path is an
54 empty string.
55 ENOTDIR
57 A component of the path prefix is not a directory.
58 The ftok() function may fail if:
61 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
63 resolution of the path argument.
64 ENAMETOOLONG
66 Pathname resolution of a symbolic link produced an intermediate
67 result whose length exceeds {PATH_MAX}.
68 The following sections are informative.
71
73 Getting an IPC Key
74 The following example gets a unique key that can be used by the IPC
75 functions semget(), msgget(), and shmget(). The key returned by ftok()
76 for this example is based on the ID value S and the pathname /tmp.
77 #include <sys/ipc.h>
80 ...
81 key_t key;
82 char *path = "/tmp";
83 int id = 'S';
84 key = ftok(path, id);
87 Saving an IPC Key
89 The following example gets a unique key based on the pathname /tmp and
90 the ID value a. It also assigns the value of the resulting key to the
91 semkey variable so that it will be available to a later call to
92 semget(), msgget(), or shmget().
93 #include <sys/ipc.h>
96 ...
97 key_t semkey;
98 if ((semkey = ftok("/tmp", 'a')) == (key_t) -1) {
101 perror("IPC error: ftok"); exit(1);
102 }
103
105 For maximum portability, id should be a single-byte character.
106
108 None.
109
111 None.
112
114 msgget(), semget(), shmget(), the Base Definitions volume of
115 IEEE Std 1003.1-2001, <sys/ipc.h>
116
118 Portions of this text are reprinted and reproduced in electronic form
119 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
120 -- Portable Operating System Interface (POSIX), The Open Group Base
121 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
122 Electrical and Electronics Engineers, Inc and The Open Group. In the
123 event of any discrepancy between this version and the original IEEE and
124 The Open Group Standard, the original IEEE and The Open Group Standard
125 is the referee document. The original Standard can be obtained online
126 at http://www.opengroup.org/unix/online.html .
127IEEE/The Open Group 2003 FTOK(3P)