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ftok(3) Library Functions Manual ftok(3) NAME ftok - Generates a standard interprocess communication key LIBRARY Standard C Library (libc.so, libc.a) SYNOPSIS #include <sys/ipc.h> key_t ftok( 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> key_t ftok( char *path_name, char project_id ); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: ftok(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies the pathname of an existing file that is accessible to the process. Specifies a value that uniquely identifies a project. DESCRIPTION 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 re- turns 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. RETURN VALUES Upon successful completion, the ftok() function returns a key. Other- wise, ftok() returns the value (key_t)-1 and sets errno to indicate the error. ERRORS The ftok() function sets errno to the specified values for the follow- ing conditions: Search permission is denied for a component of the path_name parameter. Too many symbolic links were encountered in re- solving path_name. The length of the path_name parameter exceeds PATH_MAX, or a pathname component is longer than NAME_MAX. Or, path- name 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. RELATED INFORMATION Functions: msgget(2), semget(2), shmget(2) Standards: standards(5) delim off ftok(3)