ftok - Generate a standard interprocess communication key
const char *path_name,
int project_id );
The following definition of the ftok() function does not
conform to current standards and is supported only for
#include <sys/types.h> #include <sys/ipc.h>
char project_id );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies the pathname of an existing file that is accessible
to the process. Specifies a value that uniquely
identifies a project.
The ftok() function returns a key, based on the path_name
and project_id parameters, that is usable in subsequent
calls to the msgget(), semget(), and shmget() functions.
The ftok() function returns the same key for all paths
that name the same file, when called with the same project_id
parameter. Different keys are returned for the
same file if different project_id parameters are used, or
if paths are used that name different files existing on
the same file system at the same time. If a file named by
path_name is removed and recreated with the same name, the
ftok() function may return a different key than the original
Only the low order 8-bits of project_id are significant.
The behavior of ftok() is unspecified if these bits are 0.
For maximum portability, project_id should be a singlebyte
Upon successful completion, the ftok() function returns a
key. Otherwise, ftok() returns the value (key_t)-1 and
sets errno to indicate the error.
The ftok() function sets errno to the specified values for
the following conditions: Search permission is denied for
a component of the path_name parameter. Too many symbolic
links were encountered in resolving path_name. The length
of the path_name parameter exceeds PATH_MAX, or a pathname
component is longer than NAME_MAX. Or, pathname resolution
of a symbolic link produced an intermediate result whose
length exceeds PATH_MAX. The path_name parameter points
to the name of a file that does not exist or points to an
empty string. A component of the path_name parameter is
not a directory.
Functions: msgget(2), semget(2), shmget(2)
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