add: help message

src/main.c

@@ -93,7 +93,11 @@ int main(int ac, char **av)
     struct statistics stats;
     struct setting settings;
 
-    if (get_setting(av + 1, &settings))
+    int ret = get_setting(av + 1, &settings);
+
+    if (ret == -1)
+        goto finish;
+    if (ret)
         goto error0;
 
     size_t packet_size = sizeof(struct icmphdr) + settings.payload_size;
@@ -168,6 +172,7 @@ int main(int ac, char **av)
 
     print_statistics(&stats, &settings);
 
+finish:
     return 0;
 
 error3:

src/print.c

@@ -2,6 +2,7 @@
 
 #include "icmp_error.h"
 #include "interval.h"
+#include "parsing.h"
 #include "setting.h"
 #include "statistics.h"
 #include <arpa/inet.h>
@@ -83,3 +84,17 @@ void print_recv(const struct setting *settings, const char *packet, const struct
     printf("\n");
 }
 
+void print_help(struct param *parameters)
+{
+    printf("PING [OPTION...] HOST...\n");
+    for (size_t i = 0; parameters[i].name || parameters[i].alias; i++)
+    {
+        if (parameters[i].alias)
+            printf("-%s", parameters[i].alias);
+        printf("\t");
+        if (parameters[i].name)
+            printf("--%s", parameters[i].name);
+        printf("\t");
+        printf("%s\n", parameters[i].desc);
+    }
+}

src/print.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "parsing.h"
 #include "setting.h"
 #include "statistics.h"
 #include <bits/types/struct_timeval.h>
@@ -10,3 +11,4 @@ void print_err(const char *format, ...);
 void print_header(struct setting const *settings);
 void print_statistics(struct statistics const *stats, struct setting const *settings);
 void print_recv(const struct setting *settings, const char *packet, const struct timeval *start, const struct timeval *stop, struct sockaddr_in const *sender);
+void print_help(struct param *parameters);

src/setting.c

@@ -47,6 +47,13 @@ int get_setting(char * const *av, struct setting *settings)
         {NULL, NULL, 0, NULL, NULL},
     };
     char *hostname = parsing(av, parameters);
+
+    if (parameters[0].value)
+    {
+        print_help(parameters);
+        return -1;
+    }
+
     if (hostname == NULL)
         return 1;
     settings->dest.hostname = hostname;