我目前正在尝试创建一个多客户端服务器，以使服务器能够执行C语言的读写功能。我可以使用readfds从客户端读取数据，并将其作为参数放入SELECT中。当我添加writefds时，客户端无法连接到服务器。我不确定这是什么问题，这是否是传输和接收数据的正确方法
这是我的服务器的代码
#include <stdio.h>
#include <string.h> //strlen
#include <stdlib.h>
#include <errno.h>
#include <unistd.h> //close
#include <arpa/inet.h> //close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/time.h> //FD_SET, FD_ISSET, FD_ZERO macros
#define TRUE 1
#define FALSE 0
#define PORT 8080
int main(int argc , char *argv[])
{
int opt = TRUE;
int master_socket , addrlen , new_socket , client_socket[30] ,
max_clients = 2 , activity, i , valread , sd;
int max_sd;
struct sockaddr_in address;
char buffer[1025]; //data buffer of 1K
fd_set readfds;
fd_set writefds;
char *message = "Welcome to Server\r\n";
//initialise all client_socket[] to 0 so not checked
for (i = 0; i < max_clients; i++)
{
//client_socket[i] = 0;
}
//create a master socket
if( (master_socket = socket(AF_INET , SOCK_STREAM , 0)) == 0)
{
perror("socket failed");
exit(EXIT_FAILURE);
}
if( setsockopt(master_socket, SOL_SOCKET, SO_REUSEADDR, (char *)&opt,
sizeof(opt)) < 0 )
{
perror("setsockopt");
exit(EXIT_FAILURE);
}
//type of socket created
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons( PORT );
//bind the socket to localhost port 8888
if (bind(master_socket, (struct sockaddr *)&address, sizeof(address))<0)
{
perror("bind failed");
exit(EXIT_FAILURE);
}
printf("Listener on port %d \n", PORT);
if (listen(master_socket, 3) < 0)
{
perror("listen");
exit(EXIT_FAILURE);
}
addrlen = sizeof(address);
puts("Waiting for connections ...");
for(;;)
{
//clear the socket set
FD_ZERO(&readfds);
FD_ZERO(&writefds);
//add master socket to set
FD_SET(master_socket, &readfds);
FD_SET(master_socket, &writefds);
max_sd = master_socket;
//add child sockets to set
for ( i = 0 ; i < max_clients ; i++)
{
//socket descriptor
sd = client_socket[i];
//if valid socket descriptor then add to read list
if(sd > 0)
FD_SET( sd , &readfds);
//highest file descriptor number, need it for the select function
if(sd > max_sd)
max_sd = sd;
}
//wait for an activity on one of the sockets , timeout is NULL ,
//so wait indefinitely
activity = select( max_sd + 1 , &readfds , &writefds, NULL , NULL);
if ((activity < 0) && (errno!=EINTR))
{
printf("select error");
}
if (FD_ISSET(master_socket, &readfds))
{
if ((new_socket = accept(master_socket,
(struct sockaddr *)&address, (socklen_t*)&addrlen))<0)
{
perror("accept");
exit(EXIT_FAILURE);
}
else {
printf("Connected to socket \n");
}
bzero(buffer, 1025);
int n=0;
read(new_socket, buffer, sizeof(buffer));
printf("From client: %s\t To client: ", buffer);
bzero(buffer, 1025);
//add new socket to array of sockets
for (i = 0; i < max_clients; i++)
{
//if position is empty
if( client_socket[i] == 0 )
{
client_socket[i] = new_socket;
printf("Adding to list of sockets as %d\n" , i+1);
}
}
}
else if(FD_ISSET(master_socket, &readfds)) {
printf("From client: %s\t To client : ", buffer);
bzero(buffer, 1025);
// copy server message in the buffer
while ((buffer[n++] = getchar()) != '\n')
;
write(new_socket, buffer, sizeof(buffer));
}
else{
//else its some IO operation on some other socket
for (i = 0; i < max_clients; i++)
{
sd = client_socket[i];
if (FD_ISSET( sd , &readfds))
{
//Check if it was for closing , and also read the
//incoming message
if ((valread = read( sd , buffer, 1024)) == 0)
{
close( sd );
client_socket[i] = 0;
}
//Echo back the message that came in
else
{
}
}
}
}//else
}
return 0;
}
这是客户端的代码
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#define MAX 1000
#define PORT 8080
#define SA struct sockaddr
void func(int sockfd)
{
char buff[MAX];
int n;
int firstConnect = 1;
for (;;)
{
bzero(buff, sizeof(buff));
n = 0;
if(firstConnect==1) {
printf("Enter the string : ");
firstConnect = 0;
while ((buff[n++] = getchar()) != '\n')
;
write(sockfd, buff, sizeof(buff));
}
bzero(buff, sizeof(buff));
read(sockfd, buff, sizeof(buff));
printf("From Server: %s\t To Server : ", buff);
while ((buff[n++] = getchar()) != '\n');
write(sockfd, buff, sizeof(buff));
if ((strncmp(buff, "exit", 4)) == 0)
{
printf("Client Exit...\n");
break;
}
}
}
int main()
{
printf("CLIENT");
int sockfd, connfd;
struct sockaddr_in servaddr, cli;
// socket create and varification
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
{
printf("socket creation failed...\n");
exit(0);
}
else
printf("Socket successfully created..\n");
bzero(&servaddr, sizeof(servaddr));
// assign IP, PORT
servaddr.sin_family = AF_INET;
// servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
servaddr.sin_addr.s_addr = inet_addr("127.8.1.0");
servaddr.sin_port = htons(PORT);
// connect the client socket to server socket
if (connect(sockfd, (SA*)&servaddr, sizeof(servaddr)) != 0)
{
printf("connection with the server failed...\n");
exit(0);
}
else
printf("connected to the server..\n");
// function for chat
func(sockfd);
// close the socket
close(sockfd);
}
答案 0 :(得分：1)
作为副节点，您似乎希望read对接收到的数据进行零终止。事实并非如此。接收到的数据的长度在read的返回值中，不能忽略。
似乎您还希望write找到要发送的字符串的结尾。那不会发生。您必须指定要发送的数据的确切长度，而不是包含数据的缓冲区的长度。
send/write和recv/read函数适用于二进制数据，而不是零终止的字符串，并且可以发送/接收小于指定大小的字符串，或者可能返回错误。通过不忽略返回值和处理错误以及部分读写操作来学习如何正确使用这些功能。