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ftok(3c) [sunos man page]

ftok(3C)						   Standard C Library Functions 						  ftok(3C)

NAME
ftok - generate an IPC key SYNOPSIS
#include <sys/ipc.h> key_t ftok(const char *path, int id); DESCRIPTION
The ftok() function returns a key based on path and id that is usable in subsequent calls to msgget(2), semget(2) and shmget(2). The path argument must be the pathname of an existing file that the process is able to stat(2). The ftok() function will return the same key value for all paths that name the same file, when called with the same id value, and will return different key values when called with different id values. If the file named by path is removed while still referred to by a key, a call to ftok() with the same path and id returns an error. If the same file is recreated, then a call to ftok() with the same path and id is likely to return a different key. Only the low order 8-bits of id are significant. The behavior of ftok() is unspecified if these bits are 0. RETURN VALUES
Upon successful completion, ftok() returns a key. Otherwise, ftok() returns (key_t)-1 and sets errno to indicate the error. ERRORS
The ftok() function will fail if: EACCES Search permission is denied for a component of the path prefix. ELOOP Too many symbolic links were encountered in resolving path. ENAMETOOLONG The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}. ENOENT A component of path does not name an existing file or path is an empty string. ENOTDIR A component of the path prefix is not a directory. The ftok() function may fail if: ENAMETOOLONG Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX} . USAGE
For maximum portability, id should be a single-byte character. Another way to compose keys is to include the project ID in the most significant byte and to use the remaining portion as a sequence num- ber. There are many other ways to form keys, but it is necessary for each system to define standards for forming them. If some standard is not adhered to, it will be possible for unrelated processes to unintentionally interfere with each other's operation. It is still possible to interfere intentionally. Therefore, it is strongly suggested that the most significant byte of a key in some sense refer to a project so that keys do not conflict across a given system. NOTES
Since the ftok() function returns a value based on the id given and the file serial number of the file named by path in a type that is no longer large enough to hold all file serial numbers, it may return the same key for paths naming different files on large filesystems. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
msgget(2), semget(2), shmget(2), stat(2), attributes(5), standards(5) SunOS 5.10 24 Jul 2002 ftok(3C)

Check Out this Related Man Page

FTOK(3P)						     POSIX Programmer's Manual							  FTOK(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
ftok - generate an IPC key SYNOPSIS
#include <sys/ipc.h> key_t ftok(const char *path, int id); DESCRIPTION
The ftok() function shall return a key based on path and id that is usable in subsequent calls to msgget(), semget(), and shmget(). The application shall ensure that the path argument is the pathname of an existing file that the process is able to stat(). The ftok() function shall return the same key value for all paths that name the same file, when called with the same id value, and return different key values when called with different id values or with paths that name different files existing on the same file system at the same time. It is unspecified whether ftok() shall return the same key value when called again after the file named by path is removed and recreated with the same name. Only the low-order 8-bits of id are significant. The behavior of ftok() is unspecified if these bits are 0. RETURN VALUE
Upon successful completion, ftok() shall return a key. Otherwise, ftok() shall return (key_t)-1 and set errno to indicate the error. ERRORS
The ftok() function shall fail if: EACCES Search permission is denied for a component of the path prefix. ELOOP A loop exists in symbolic links encountered during resolution of the path argument. ENAMETOOLONG The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}. ENOENT A component of path does not name an existing file or path is an empty string. ENOTDIR A component of the path prefix is not a directory. The ftok() function may fail if: ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument. ENAMETOOLONG Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}. The following sections are informative. EXAMPLES
Getting an IPC Key The following example gets a unique key that can be used by the IPC functions semget(), msgget(), and shmget(). The key returned by ftok() for this example is based on the ID value S and the pathname /tmp. #include <sys/ipc.h> ... key_t key; char *path = "/tmp"; int id = 'S'; key = ftok(path, id); Saving an IPC Key The following example gets a unique key based on the pathname /tmp and the ID value a. It also assigns the value of the resulting key to the semkey variable so that it will be available to a later call to semget(), msgget(), or shmget(). #include <sys/ipc.h> ... key_t semkey; if ((semkey = ftok("/tmp", 'a')) == (key_t) -1) { perror("IPC error: ftok"); exit(1); } APPLICATION USAGE
For maximum portability, id should be a single-byte character. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
msgget(), semget(), shmget(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/ipc.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 FTOK(3P)
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