c语言udp通信实例（linux）

server

---------------


#include <stdio.h>          /* These are the usual header files */
#include <string.h>
#include <unistd.h>         /* for close() */
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define PORT 1234   /* Port that will be opened */
#define MAXDATASIZE 100   /* Max number of bytes of data */

main()
{
int sockfd; /* socket descriptors */
struct sockaddr_in server; /* server's address information */
struct sockaddr_in client; /* client's address information */
socklen_t sin_size;
int num;
char recvmsg[MAXDATASIZE]; /* buffer for message */
char sendmsg[MAXDATASIZE];
char condition[] = "quit";
/* Creating UDP socket */
if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
/* handle exception */
perror("Creating socket failed.");
exit(1);
}

bzero(&server,sizeof(server));
server.sin_family=AF_INET;
server.sin_port=htons(PORT);
server.sin_addr.s_addr = htonl (INADDR_ANY);
if (bind(sockfd, (struct sockaddr *)&server, sizeof(struct sockaddr)) == -1) {
/* handle exception */
perror("Bind error.");
exit(1);
}

sin_size=sizeof(struct sockaddr_in);
while (1)   {
num = recvfrom(sockfd,recvmsg,MAXDATASIZE,0,(struct sockaddr *)&client,&sin_size);

if (num < 0){
perror("recvfrom error\n");
exit(1);
}

recvmsg[num] = '\0';
printf("You got a message (%s) from %s\n",recvmsg,inet_ntoa(client.sin_addr) ); /* prints client's IP */
        if(strcmp(recvmsg,condition)==0) break;
   int i=0;
for(i = 0 ; i < num ; i ++)
{
   sendmsg[i] = recvmsg[num-1-i];
}
sendmsg[num]='\0';
sendto(sockfd,sendmsg,strlen(sendmsg),0,(struct sockaddr *)&client,sin_size);

}

close(sockfd);   /* close listenfd */
}


---------------------------------------------------------

client


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
        #include <strings.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>        /* netbd.h is needed for struct hostent =) */

#define PORT 1234   /* Open Port on Remote Host */
#define MAXDATASIZE 100   /* Max number of bytes of data */

int main(int argc, char *argv[])
{
int fd, numbytes;   /* files descriptors */
char recvbuf[MAXDATASIZE]; /* buf will store received text */
        char sendbuf[MAXDATASIZE];
struct hostent *he;         /* structure that will get information about remote host */
struct sockaddr_in server,client; /* server's address information */

if (argc !=2) { /* this is used because our program will need two argument (IP address and a message */
printf("Usage: %s  \n",argv[0]);
exit(1);
}

if ((he=gethostbyname(argv[1]))==NULL){ /* calls gethostbyname() */
printf("gethostbyname() error\n");
exit(1);
}

if ((fd=socket(AF_INET, SOCK_DGRAM, 0))==-1){ /* calls socket() */
printf("socket() error\n");
exit(1);
}

bzero(&server,sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(PORT); /* htons() is needed again */
server.sin_addr = *((struct in_addr *)he->h_addr); /*he->h_addr passes "*he"'s info to "h_addr" */

        socklen_t len;
         len=sizeof(struct sockaddr_in);
while (1) {
   printf("input message:");
         fgets(sendbuf,40,stdin);
sendto(fd,sendbuf,strlen(sendbuf),0,(struct sockaddr *)&server,len);
if ((numbytes=recvfrom(fd,recvbuf,MAXDATASIZE,0,(struct sockaddr *)&server,&len)) == -1){ /* calls recvfrom() */
printf("recvfrom() error\n");
exit(1);
}
recvbuf[numbytes]='\0';
printf("Server Return Reverse Message: %s\n",recvbuf); /* it prints server's welcome message */

}

close(fd);   /* close fd */
}


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./client 127.0.0.1

input:test