ftok - Generates a standard interprocess communication key
Standard C Library (libc.so, libc.a)
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 backward compatibility:
#include <sys/types.h> #include <sys/ipc.h>
char project_id );
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 one.
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 single-byte character.
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)
Standards: standards(5) delim off