我正在使用Ubuntu 12.05。我一直在尝试通过C套接字编程实现Stop和wait协议。我创建了两个程序，一个是服务器，另一个是客户端。通过评论
解释了代码的预期工作serversocket.c
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <error.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>
int main(int argc,char *argv[])
{
int listenfd = 0,qlength=10,connfd = 0,t=5;
int n;
struct sockaddr_in serv;
struct sockaddr_in dest;
socklen_t socksize = sizeof(struct sockaddr_in);
char sendBuff[1024]="hi\n";
//time_t ticks;
listenfd = socket(AF_INET,SOCK_STREAM,0); //socket for listening to connection requests
memset(&serv,'0',sizeof(serv));
serv.sin_family = AF_INET;
serv.sin_addr.s_addr = htonl(INADDR_ANY);
serv.sin_port=htons(5000);
bind(listenfd,(struct sockaddr *)&serv,sizeof(serv)); //binding the socket to a port
listen(listenfd,2);
connfd=accept(listenfd,(struct sockaddr *)&dest,&socksize); //another socket for sending and receiving on the previously built socket
while(connfd){
printf("Incoming connection from %s-sending a hi...\n",inet_ntoa(dest.sin_addr));
send(connfd,sendBuff,strlen(sendBuff),0); //at first my server sends a hi
sleep(3);
n=recv(connfd,sendBuff,1024,0); //if hi received by the client,then server should receive "Message Received" from the client
sendBuff[n]='\0';
printf("%s",sendBuff);
connfd=accept(listenfd,(struct sockaddr *)&dest,&socksize); }
return 0;
}
clientsocket.c
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
int sockfd = 0, n = 0,m=2;
char recvBuff[1024];
struct sockaddr_in serv_addr;
if(argc != 2)
{
printf("\n Usage: %s <ip of server> \n",argv[0]);
return 1;
}
memset(recvBuff, '0',sizeof(recvBuff));
if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
printf("\n Error : Could not create socket \n");
return 1;
}
memset(&serv_addr, '0', sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(5000);
if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
{
printf("\n inet_pton error occured\n");
return 1;
}
if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
{
printf("\n Error : Connect Failed \n");
return 1;
}
while(m--){ //m is 2 initially,I want that sending and receiving should be done 2 times
n = recv(sockfd,recvBuff,1024,0);
recvBuff[n]='\0'; //"hi" is received
printf("%s",recvBuff);
if(recvBuff=="hi\n")
send(sockfd,"Message Received",strlen("Message Received\n"),0);} //sending "Message received"
return 0;
}
现在从服务器向客户端发送消息的工作正常，但是客户端到服务器（收到消息）正在产生问题。无论是给出错误还是正确结果，它只是给出一个空白屏幕。
答案 0 :(得分：1)
您无法使用“==”运算符比较字符串。
您需要使用strcmp()
...所以
if( strcmp( recvBuff, "hi\n" ) == 0 )
send(sockfd,"Message Received",strlen("Message Received\n"),0);
else
printf( "[%s] != [hi\n]\n", recvBuff );
答案 1 :(得分：1)
基本上，您的代码中有三个不同的问题：
'\n'个功能中添加printf。accept函数。从man accept page开始，我们可以阅读
accept()函数将提取第一个连接 挂起连接队列，创建一个具有相同套接字的新套接字 键入协议和地址族作为指定的套接字，并分配 该套接字的新文件描述符。
因此，在第一次通信之后，您的服务器正在等待新连接，并且您的客户端正在等待来自服务器的消息。第二次沟通永远不会发生。
要解决此问题，您可以使用fork() API。
以下是使用fork()的修正提案：
clientsocket.c
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
int sockfd = 0, n = 0,m=2;
char recvBuff[1024];
struct sockaddr_in serv_addr;
if(argc != 2)
{
printf("\n Usage: %s <ip of server> \n",argv[0]);
return 1;
}
memset(recvBuff, '0',sizeof(recvBuff));
if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
printf("\n Error : Could not create socket \n");
return 1;
}
memset(&serv_addr, '0', sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(5000);
if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
{
printf("\n inet_pton error occured\n");
return 1;
}
if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
{
printf("\n Error : Connect Failed \n");
return 1;
}
//m is 2 initially,I want that sending and receiving should be done 2 times
while(m--)
{
printf("Waiting from the server ...\n");
n = recv(sockfd,recvBuff,1024,0);
recvBuff[n]= '\0'; //"hi" is received
printf("%s\n", recvBuff);
if(!strncmp(recvBuff, "hi\n", strlen("hi\n")))
{
printf("Send ACK\n");
n = send(sockfd,"Message Received",strlen("Message Received\n"),0);
printf("%d Sent ... \n", n);
}
} //sending "Message received"
return 0;
}
serversocket.c
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <error.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>
int main(int argc,char *argv[])
{
int listenfd = 0,qlength=10,connfd = 0,t=5;
int n;
struct sockaddr_in serv;
struct sockaddr_in dest;
socklen_t socksize = sizeof(struct sockaddr_in);
char sendBuff[1024]="hi\n";
pid_t pid;
int m = 2;
//time_t ticks;
listenfd = socket(AF_INET,SOCK_STREAM,0); //socket for listening to connection requests
memset(&serv,'0',sizeof(serv));
serv.sin_family = AF_INET;
serv.sin_addr.s_addr = htonl(INADDR_ANY);
serv.sin_port=htons(5000);
bind(listenfd,(struct sockaddr *)&serv,sizeof(serv)); //binding the socket to a port
printf("Server started ...\n");
listen(listenfd,2);
connfd=accept(listenfd,(struct sockaddr *)&dest,&socksize); //another socket for sending and receiving on the previously built socket
while(connfd > 0)
{
printf("Incoming connection from %s-sending a hi...\n",inet_ntoa(dest.sin_addr));
pid = fork();
if(pid) {
/* shall continue to listen to new client */
printf("Parent shall continue listening ... \n");
connfd=accept(listenfd,(struct sockaddr *)&dest,&socksize);
} else {
printf("Chlid process: Communication with the client ... \n");
while(m--)
{
printf("try %d - Sending %s ... \n", m, sendBuff);
send(connfd,sendBuff,strlen(sendBuff),0); //at first my server sends a hi
sleep(3);
n=recv(connfd, sendBuff, 1024, 0); //if hi received by the client,then server should receive "Message Received" from the client
sendBuff[n]='\0';
printf("Data received: [%s]\n", sendBuff); /* need to add '\n' so the print will be displayed */
strcpy(sendBuff, "hi\n");
}
printf("Child process will exit\n");
return 0;
}
}
return 0;
}