Use sysconf() instead of HOST_NAME_MAX

hostname.c

@@ -15,7 +15,16 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
-	char host[HOST_NAME_MAX + 1];
+	long sz;
+	char *host;
+
+	sz = sysconf(_SC_HOST_NAME_MAX);
+	if (sz < 0)
+		sz = 255;
+
+	host = malloc(sz + 1);
+	if (!host)
+		eprintf("malloc:");
 
 	ARGBEGIN {
 	default:
@@ -23,13 +32,15 @@ main(int argc, char *argv[])
 	} ARGEND;
 
 	if (argc < 1) {
-		if (gethostname(host, sizeof(host)) < 0)
+		if (gethostname(host, sz + 1) < 0)
 			eprintf("gethostname:");
 		puts(host);
 	} else {
-		if (sethostname(argv[0], strlen(argv[0])) < 0)
+		if (sethostname(argv[0], sz + 1) < 0)
 			eprintf("sethostname:");
 	}
 
+	free(host);
+
 	return EXIT_SUCCESS;
 }