first commit

.gitignore

@@ -0,0 +1 @@
+# tc

udpClient.c

@@ -0,0 +1,75 @@
+//https://blog.csdn.net/xiongping_/article/details/47722049
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+
+#define PORT 45454
+#define MAXDATASIZE 100
+
+int main(int argc, char *argv[])
+{
+    int sockfd, num;
+    char buf[MAXDATASIZE];
+
+    struct hostent *he;
+    struct sockaddr_in server,peer;
+
+    if (argc !=3)
+    {
+        printf("Usage: %s <IP Address><message>\n",argv[0]);
+        exit(1);
+    }
+
+    if ((he=gethostbyname(argv[1]))==NULL)
+    {
+        printf("gethostbyname()error\n");
+        exit(1);
+    }
+
+    // if ((he=gethostbyname("127.0.0.1"))==NULL)
+    // {
+    //     printf("gethostbyname()error\n");
+    //     exit(1);
+    // }
+
+    if ((sockfd=socket(AF_INET, SOCK_DGRAM,0))==-1)
+    {
+        printf("socket() error\n");
+        exit(1);
+    }
+
+    bzero(&server,sizeof(server));
+    server.sin_family = AF_INET;
+    server.sin_port = htons(PORT);
+    server.sin_addr= *((struct in_addr *)he->h_addr);
+    
+    sendto(sockfd, argv[2],strlen(argv[2]),0,(struct sockaddr *)&server,sizeof(server));
+    
+    socklen_t  addrlen;
+    addrlen=sizeof(server);
+    while (1)
+    {
+        if((num=recvfrom(sockfd,buf,MAXDATASIZE,0,(struct sockaddr *)&peer,&addrlen))== -1)
+        {
+            printf("recvfrom() error\n");
+            exit(1);
+        }
+        if (addrlen != sizeof(server) ||memcmp((const void *)&server, (const void *)&peer,addrlen) != 0)
+        {
+            printf("Receive message from otherserver.\n");
+            continue;
+        }
+
+        buf[num]='\0';
+        printf("Server Message:%s\n",buf);
+        break;
+    }
+
+    close(sockfd);
+}