我正在尝试编写的程序需要帮助。该程序应该有3个客户端通过套接字连接到它。
我正在寻找一些方向。
如何等待服务器程序连接到所有3个客户端。
如何区分连接。即写入客户端1但不写入2或写入所有客户端连接。
如何使用fork（）。
我能够编写服务器和客户端程序，但我无法想到多个客户端的解决方案。
如果有人可以帮我解决这个问题，那将会很棒。非常感谢你。
编辑：到目前为止，我有服务器程序等到3个客户端已连接。所有3个客户端完成但服务器程序显示“从套接字读取错误：错误的文件描述符”
我的客户端代码如下所示：
#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>
void error(const char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
char router_no[256] = "0";
int cost_to_router_0 = 0;
int cost_to_router_1 = 1;
int cost_to_router_2 = 3;
int cost_to_router_3 = 7;
printf("\n\n");
printf("Initial table for Router 0(Client)\n");
printf("===================================================\n");
printf("Destination Router |Link Cost |\n");
printf("===================================================\n");
printf("Router 0 |%d |\n", cost_to_router_0);
printf("Router 1 |%d |\n", cost_to_router_1);
printf("Router 2 |%d |\n", cost_to_router_2);
printf("Router 3 |%d |\n", cost_to_router_3);
printf("===================================================\n");
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[256];
if (argc < 3) {
fprintf(stderr,"usage %s hostname port\n", argv[0]);
exit(0);
}
portno = atoi(argv[2]);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
printf("\n");
printf("Clients Router Number: %s \n", router_no);
printf("Cost to Router 0(Client): %d \n", cost_to_router_0);
printf("Cost to Router 1(Server): %d \n", cost_to_router_1);
printf("Cost to Router 2: %d \n", cost_to_router_2);
printf("Cost to Router 3: %d \n", cost_to_router_3);
printf("\n");
//printf("Please enter the message: ");
//bzero(buffer,256);
//fgets(buffer,255,stdin);
// Send Router Number
n = write(sockfd,router_no,strlen(router_no));
if (n < 0)
error("ERROR writing to socket");
// Send Cost of Router 0 to other Routers
n = write(sockfd, &cost_to_router_1, sizeof(cost_to_router_1));
n = write(sockfd, &cost_to_router_2, sizeof(cost_to_router_2));
n = write(sockfd, &cost_to_router_3, sizeof(cost_to_router_3));
if (n < 0)
error("ERROR writing to socket");
int cost_server_to_router_0 = 0;
int cost_server_to_router_1 = 0;
int cost_server_to_router_2 = 0;
int cost_server_to_router_3 = 0;
bzero(buffer,256);
n = read(sockfd, &cost_server_to_router_0, sizeof(cost_server_to_router_0));
n = read(sockfd, &cost_server_to_router_0, sizeof(cost_server_to_router_1));
n = read(sockfd, &cost_server_to_router_2, sizeof(cost_server_to_router_2));
n = read(sockfd, &cost_server_to_router_3, sizeof(cost_server_to_router_3));
printf("Costs of Router 1(Server) to other Routers\n");
printf("Cost to Router 0: %d \n", cost_server_to_router_0);
printf("Cost to Router 1: %d \n", cost_server_to_router_1);
printf("Cost to Router 2: %d \n", cost_server_to_router_2);
printf("Cost to Router 3: %d \n", cost_server_to_router_3);
bzero(buffer,256);
n = read(sockfd,buffer,255);
if ( cost_to_router_1 + cost_server_to_router_0 < cost_to_router_0)
cost_to_router_0 = cost_to_router_1 + cost_server_to_router_0;
if ( cost_to_router_1 + cost_server_to_router_1 < cost_to_router_1)
cost_to_router_1 = cost_to_router_1 + cost_server_to_router_1;
if ( cost_to_router_1 + cost_server_to_router_2 < cost_to_router_2)
cost_to_router_2 = cost_to_router_1 + cost_server_to_router_2;
if ( cost_to_router_1 + cost_server_to_router_3 < cost_to_router_3)
cost_to_router_3 = cost_to_router_1 + cost_server_to_router_3;
printf("\n\n");
printf("Updated table for Router 0(Client)\n");
printf("===================================================\n");
printf("Destination Router |Link Cost |\n");
printf("===================================================\n");
printf("Router 0 |%d |\n", cost_to_router_0);
printf("Router 1 |%d |\n", cost_to_router_1);
printf("Router 2 |%d |\n", cost_to_router_2);
printf("Router 3 |%d |\n", cost_to_router_3);
printf("===================================================\n");
if (n < 0)
error("ERROR reading from socket");
printf("%s\n",buffer);
close(sockfd);
return 0;
}
请记住，这是我使用我发现的教程编写的单个处理客户端程序。我需要能够修改它以连接并保持与多个客户端的连接
我的服务器代码如下：
/* A simple server in the internet domain using TCP
The port number is passed as an argument */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
void error(const char *msg)
{
perror(msg);
exit(1);
}
int main(int argc, char *argv[])
{
int number_of_clients = 0;
char router_no[256] = "1";
int cost_to_router_0 = 1;
int cost_to_router_1 = 0;
int cost_to_router_2 = 1;
int cost_to_router_3 = 10000; // This is set to 10,000 because there is not link
// between router 1 to router 3 and/but infinity
// is not a real number.
int sockfd, newsockfd, portno;
socklen_t clilen;
char buffer[256];
struct sockaddr_in serv_addr, cli_addr;
int n;
if (argc < 2) {
fprintf(stderr,"ERROR, no port provided\n");
exit(1);
}
// Socket is opened
sockfd = socket(AF_INET, SOCK_STREAM, 0);
// Displays error if socket opening was not suscessful
if (sockfd < 0)
error("ERROR opening socket");
// Sets serv_addr to zeros
bzero((char *) &serv_addr, sizeof(serv_addr));
// Sets port number to argument passed in call
portno = atoi(argv[1]);
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);
// Biding socket to an adress
if (bind(sockfd, (struct sockaddr *) &serv_addr,
sizeof(serv_addr)) < 0)
error("ERROR on binding");
listen(sockfd,5);
clilen = sizeof(cli_addr);
while (1)// start of while
{
while (number_of_clients < 3)
{
newsockfd = accept(sockfd,
(struct sockaddr *) &cli_addr,
&clilen);
if (newsockfd < 0)
error("ERROR on accept");
else number_of_clients ++;
}
bzero(buffer,256);
n = read(newsockfd,buffer,255);
if (n < 0) error("ERROR reading from socket");
printf("Client Router's Number: %s\n", buffer);
int cost_client_to_router_1 = 0;
int cost_client_to_router_2 = 0;
int cost_client_to_router_3 = 0;
bzero(buffer,256);
n = read(newsockfd, &cost_client_to_router_1, sizeof(cost_client_to_router_1));
n = read(newsockfd, &cost_client_to_router_2, sizeof(cost_client_to_router_2));
n = read(newsockfd, &cost_client_to_router_3, sizeof(cost_client_to_router_3));
if (n < 0) error("Error reading from socket");
printf("Cost from client to router 1: %d \n", cost_client_to_router_1);
printf("Cost from client to router 2: %d \n", cost_client_to_router_2);
printf("Cost from client to router 3: %d \n", cost_client_to_router_3);
n = write(newsockfd, &cost_to_router_0, sizeof(cost_to_router_0));
n = write(newsockfd, &cost_to_router_0, sizeof(cost_to_router_0));
n = write(newsockfd, &cost_to_router_2, sizeof(cost_to_router_2));
n = write(newsockfd, &cost_to_router_3, sizeof(cost_to_router_3));
if (n < 0) error("ERROR writing to socket");
close(newsockfd);
} //end of while
close(sockfd);
return 0;
}
服务器代码无法正常工作，因为我缺少对fork（）和select（）
的理解答案 0 :(得分：1)
如何等待服务器程序连接到所有3个客户端。
通过三次致电accept。
如何区分连接。即写入客户端1但不写入2或写入所有客户端连接。
它们都有accept返回的不同文件描述符。您当前的服务器代码会忘记前两个（通过覆盖newsockfd）并仅将最后一个存储在newsockfd中。不要这样做，原因很明显。
如何使用fork（）。
这还不足以得到答案。
所有3个客户端完成但服务器程序显示“从套接字读取错误：错误的文件描述符”
那是因为服务器关闭了最后一个客户端的文件描述符（记住它忘了前两个），然后不等待另一个客户端（因为number_of_clients已经是3），然后尝试从文件中读取描述它刚关闭。