/*
         * gethostname  --
         *
         */

        #ifdef  SVR4 
        #include <sys/systeminfo.h>
        #endif  /* SVR4 */ 

                ....

                char buf[MAXHOSTNAME]

        #ifdef  SVR4
                if (sysinfo(SI_HOSTNAME, buf, sizeof(buf)) <0) {
                        perror("SI_HOSTNAME");
                        exit(BAD);
                }
        #else   /* Assume BSD */
                if (gethostname(buf, sizeof(buf)) < 0) {
                        perror("gethostname");
                        exit(BAD);
                }
        #endif  /* SVR4 */

        /* buf has hostname here... */