Originální popis anglicky:
ftok - generate an IPC key
Návod, kniha: POSIX Programmer's Manual
#include <sys/ipc.h>
key_t ftok(const char *
path, int
id);
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.
Upon successful completion,
ftok() shall return a key. Otherwise,
ftok() shall return (
key_t)-1 and set
errno to indicate
the error.
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.
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);
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);
}
For maximum portability,
id should be a single-byte character.
None.
None.
msgget() ,
semget() ,
shmget() , the Base Definitions
volume of IEEE Std 1003.1-2001,
<sys/ipc.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- 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
.
