gethostid 的实现

static long gethostid(void)
{
   long result = 0;
    char name[1024];
    struct hostent *hent = NULL;
    char **p = NULL;
    struct in_addr in;
    if (gethostname(name, 1024) == 0)
    {
if ((hent = gethostbyname(name)) != NULL)
{
            p = hent->h_addr_list;
            if (p && *p)
            {
                (void) memcpy(&in.s_addr, *p, sizeof(in.s_addr));
                result = (long)in.s_addr;
            }
        }
    }
   return result;
}

man page 上这样子描述

GETHOSTID(2)               Linux Programmer's Manual              GETHOSTID(2)


NAME
       gethostid, sethostid - get or set the unique identifier of the current host


SYNOPSIS
       #include <unistd.h>


       long gethostid(void);
       int sethostid(long hostid);


DESCRIPTION
       Get  or  set  a unique 32-bit identifier for the current machine.  The 32-bit identifier is intended to be unique among all UNIX systems in existence. This
       normally resembles the Internet address for the local machine, as returned by gethostbyname(3), and thus usually never needs to be set.


       The sethostid() call is restricted to the superuser.


       The hostid argument is stored in the file /etc/hostid.


RETURN VALUE
       gethostid() returns the 32-bit identifier for the current host as set by sethostid(2).


CONFORMING TO
       4.2BSD; these functions were dropped in 4.4BSD.  SVr4 includes gethostid() but not sethostid().  POSIX.1-2001 specifies gethostid() but not sethostid().


FILES
       /etc/hostid


EXAMPLE
       id = gethostid ();


       /* This is a no-op unless unsigned int is wider than 32 bits.  */
       id &= 0xffffffff;


SEE ALSO
       hostid(1), gethostbyname(3)

在移植Linux应用到其他系统时，因为没有这个函数，往往要自己实现这个函数，下面给出一个实现方法：