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ftok(3) [osx man page]

FTOK(3) 						   BSD Library Functions Manual 						   FTOK(3)

ftok -- create IPC identifier from path name LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/ipc.h> key_t ftok(const char *path, int id); DESCRIPTION
The ftok() function attempts to create a unique key suitable for use with the semget(2), and shmget(2) functions, given the path of an exist- ing file and a user-selectable id. The specified path must specify an existing file that is accessible to the calling process or the call will fail. Also, note that links to files will return the same key, given the same id. RETURN VALUES
The ftok() function will return -1 if path does not exist or if it cannot be accessed by the calling process. LEGACY SYNOPSIS
#include <sys/types.h> #include <sys/ipc.h> The include file <sys/types.h> is necessary. SEE ALSO
semget(2), shmget(2), compat(5) HISTORY
The ftok() function originates with System V and is typically used by programs that use the System V IPC routines. AUTHORS
Thorsten Lockert <> BUGS
The returned key is computed based on the device minor number and inode of the specified path, in combination with the lower 8 bits of the given id. Thus, it is quite possible for the routine to return duplicate keys. BSD
July 9, 2009 BSD

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

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
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 . IEEE
/The Open Group 2003 FTOK(3P)
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