сгенерировать ключ IPC (generate an IPC key)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
ftok — generate an IPC key
Синопсис (Synopsis)
#include <sys/ipc.h>
key_t ftok(const char *path, int id);
Описание (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(), with the exception that if stat() would fail with
[EOVERFLOW] due to file size, ftok() shall still succeed.
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
should 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.
Возвращаемое значение (Return value)
Upon successful completion, ftok() shall return a key. Otherwise,
ftok() shall return (key_t)-1 and set errno to indicate the
error.
Ошибки (Error)
The ftok() function shall fail if:
EACCES Search permission is denied for a component of the path
prefix.
EIO An error occurred while reading from the file system.
ELOOP A loop exists in symbolic links encountered during
resolution of the path argument.
ENAMETOOLONG
The length of a component of a pathname 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 names an existing file that
is neither a directory nor a symbolic link to a directory,
or the path argument contains at least one non-<slash>
character and ends with one or more trailing <slash>
characters and the last pathname component names an
existing file that is neither a directory nor a symbolic
link to a directory.
The ftok() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
The following sections are informative.
Примеры (Examples)
Getting an IPC Key
The following example gets a 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);
}
Использование в приложениях (Application usage)
For maximum portability, id should be a single-byte character.
Applications should not assume that the resulting key value is
unique.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
Future versions of this standard may add new interfaces to
provide unique keys.
Смотри также (See also)
msgget(3p), semget(3p), shmget(3p)
The Base Definitions volume of POSIX.1‐2017, sys_ipc.h(0p)
