First commit

common/DieWithMessage.c

@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void DieWithUserMessage(const char *msg, const char *detail) {
+    fputs(msg, stderr);
+    fputs(": ", stderr);
+    fputs(detail, stderr);
+    fputc('\n', stderr);
+    exit(1);
+}
+
+void DieWithSystemMessage(const char *msg) {
+    perror(msg);
+    exit(1);
+}
+

common/Practical.c

@@ -0,0 +1,12 @@
+#include <netdb.h>
+#include <stddef.h>
+
+#include "Practical.h"
+
+int proto_get_num(const char *name) {
+    struct protoent *protoent = getprotobyname(name);
+    if (protoent == NULL) {
+        DieWithSystemMessage("getprotobyname");
+    }
+    return protoent->p_proto;
+}

common/Practical.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#define BUFSIZE 512
+
+void DieWithUserMessage(const char *msg, const char *detail);
+void DieWithSystemMessage(const char *msg);
+int proto_get_num(const char *name);