преобразовать путь и идентификатор проекта в ключ System V IPC (convert a pathname and a project identifier to a System V IPC key)
Имя (Name)
ftok - convert a pathname and a project identifier to a System V
IPC key
Синопсис (Synopsis)
#include <sys/ipc.h>
key_t ftok(const char *pathname, int proj_id);
Описание (Description)
The ftok() function uses the identity of the file named by the
given pathname (which must refer to an existing, accessible file)
and the least significant 8 bits of proj_id (which must be
nonzero) to generate a key_t type System V IPC key, suitable for
use with msgget(2), semget(2), or shmget(2).
The resulting value is the same for all pathnames that name the
same file, when the same value of proj_id is used. The value
returned should be different when the (simultaneously existing)
files or the project IDs differ.
Возвращаемое значение (Return value)
On success, the generated key_t value is returned. On failure -1
is returned, with errno indicating the error as for the stat(2)
system call.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ftok() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008.
Примечание (Note)
On some ancient systems, the prototype was:
key_t ftok(char *pathname, char proj_id);
Today, proj_id is an int, but still only 8 bits are used.
Typical usage has an ASCII character proj_id, that is why the
behavior is said to be undefined when proj_id is zero.
Of course, no guarantee can be given that the resulting key_t is
unique. Typically, a best-effort attempt combines the given
proj_id byte, the lower 16 bits of the inode number, and the
lower 8 bits of the device number into a 32-bit result.
Collisions may easily happen, for example between files on
/dev/hda1 and files on /dev/sda1.
Примеры (Examples)
See semget(2).
Смотри также (See also)
msgget(2), semget(2), shmget(2), stat(2), sysvipc(7)
