linux系统调用之ftok()

ftok原型如下： key_t ftok( char * fname, int id ) fname就时你指定的文件名，id是子序号。 失败返回值为-1 ftok应用范围:在IPC通信及消息记者中使用 解析: 系统建立IPC通讯（如消息队列、共享内存时）必须指定一个ID值。通常情况下，该id值通过ftok函数得到。 在一般的UNIX实现中，是将文件的索引节点号取出，前面加上子序号得到key_t的返回值。 如指定文件的索引节点号为65538，换算成16进制为0x010002，而你指定的ID值为38，换算成16进制为0x26，则最后的key_t返回值为0x26010002。 查询文件索引节点号可通过命令： ls -i来查看 nux Programmer's Manual                   FTOK(3)                                                                                                                                        NAME        ftok - convert a pathname and a project identifier to a System V IPC        key                                                                                                                                        SYNOPSIS        # include <sys/types.h>        # include <sys/ipc.h>                                                                                                                                               key_t ftok(const char *pathname, int proj_id);                                                                                                                                        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.                                                                                                                                        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.                                                                                                                                        CONFORMING TO        XPG4                                                                                                                                        NOTES        Under libc4 and libc5 (and under SunOS 4.x) 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 behaviour is said to be        undefined when proj_id is zero.