我是网络编程的新手。我必须用 C 编写一个简单的客户端/服务器程序。服务器将侦听连接，客户端将连接到服务器，发送消息，并接收来自客户端的回显。我们必须使用 select() 更新它以同时处理从服务器进程到多个客户端的连接。我尝试按照指示在客户端实现 select()，但我认为我在客户端有一个无限循环if(FD_ISSET(clientSockfd, &readfds))。
//client1.c
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <resolv.h>
#include <arpa/inet.h>
const int BUF_SIZE = 512;
int main(int argc, char *argv[]) {
char buf[BUF_SIZE], buf2[BUF_SIZE];
char *msg;
struct sockaddr_in serverInfo;
int clientSockfd, errorCheck, readVal, numfd;
struct hostent *hostName;
fd_set readfds;
//make sure user entered correct arguments when starting client
if(argc != 3)
{
printf("error: must enter 'programName portNumber hostname'\n");
exit(errno);
}
//create socket and error check socket() call
clientSockfd=socket(AF_INET, SOCK_STREAM, 0);
if (clientSockfd == -1)
{
perror("error creating socket");
exit(errno);
}
//assign sockaddr_in info for RemoteAddr
bzero(&serverInfo, sizeof(serverInfo));
serverInfo.sin_family=AF_INET;
hostName=gethostbyname(argv[2]);
if(hostName == NULL)
{
herror("Error when calling gethostbyname()");
exit(errno);
}
memcpy((unsigned char *) &serverInfo.sin_addr, (unsigned char *)hostName->h_addr, hostName->h_length); //copy IP address to be used
serverInfo.sin_port=htons(atoi(argv[1])); //port number to be used, given in command line, must be converted to network byte order
//connect to server side
if(connect(clientSockfd, (struct sockaddr *)&serverInfo, sizeof(serverInfo)) == -1)
{
perror("error when connecting to server");
exit(errno);
}
while(1)
{
FD_ZERO(&readfds); //zero out set
FD_SET(fileno(stdin), &readfds);
FD_SET(clientSockfd, &readfds);
int maxfd = fileno(stdin);
if(maxfd < clientSockfd) maxfd = clientSockfd;
numfd = select(maxfd, &readfds, 0, 0, 0); //call select()
if(numfd > 0)
{
if(FD_ISSET(clientSockfd, &readfds))
{
//make sure buf is empty so it doesnt print extra chars
bzero(buf2, BUF_SIZE);
read(clientSockfd, buf2, BUF_SIZE);
}
if(FD_ISSET(fileno(stdin), &readfds))
{
bzero(buf, BUF_SIZE);
fgets(buf, BUF_SIZE-1, stdin);
printf("echo from server: %s\n", buf);
errorCheck = write(clientSockfd, buf, strlen(buf)+1);
if(errorCheck == -1)
{
perror("error writing");
}
}
}
else if(numfd == 0)
{
perror("Error using select()\n");
exit(0);
}
else
printf("no data\n");
}
//close connection to server
errorCheck = close(clientSockfd);
if(errorCheck == -1)
{
perror("Error closing connection.");
exit(errno);
}
return 0;
}
这是服务器..
//server.c
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/socket.h>
#include <resolv.h>
#include <arpa/inet.h>
#include <errno.h>
const int ASSIGNED_PORT = 17000;
const int BUF_SIZE = 512;
int main() {
int serverfd, clientfd;
struct sockaddr_in serverSock; //NOTE: a pointer to sockaddr_in can be cast to a pointer to
// a struct sockaddr - useful for connect()
char buf[BUF_SIZE];
int errorCheck, msgLength;
//create socket with error checking (-1 ret on error)
serverfd = socket(AF_INET, SOCK_STREAM, 0);
if(serverfd < 0 )
{
perror("socket failed.");
exit(errno);
}
//assign sockaddr_in info for server
bzero(&serverSock, sizeof(serverSock)); //set to all 0's
serverSock.sin_family = AF_INET;
serverSock.sin_addr.s_addr = htonl(INADDR_ANY);
serverSock.sin_port = htons(ASSIGNED_PORT);
//bind a name to the socket with error checking (0 ret on success)
errorCheck = bind(serverfd, (struct sockaddr*)&serverSock, sizeof(serverSock));
if(errorCheck < 0 )
{
perror("bind failed.");
exit(errno);
}
//listen for connections with error checking (0 ret on success)
errorCheck = listen(serverfd, 10);
if(errorCheck < 0 )
{
perror("listen failed.");
exit(errno);
}
printf("Listening for connections. Enter CNTRL-c to kill server.\n");
//create infinite loop to accept, read, write, and close connections with error hecking
while(1)
{
//accept the connection from the client
clientfd = accept(serverfd, 0, 0);
if(clientfd == -1)
{
perror("error accepting connection.");
exit(errno);
}
//read data from the client
bzero(buf, BUF_SIZE);
msgLength = read(clientfd, buf, BUF_SIZE-1);
if(msgLength == -1)
{
perror("error reading from client");
close(clientfd);
close(serverfd);
exit(errno);
}
if(buf[0] '\0')
{
printf("connection closing");
exit(0);
}
//print what the client sent
printf("Message from client: %s\n", buf);
//echo back what the client sent
errorCheck = write(clientfd, buf, strlen(buf)+1);
if(errorCheck == -1 )
{
perror("error writing to client");
exit(errno);
}
//close the connection
errorCheck = close(clientfd);
if(errorCheck == -1)
{
perror("error closing connection");
exit(errno);
}
}
errorCheck = close(serverfd);
if(errorCheck==-1)
{
perror("error closing server, exiting program now");
sleep(6);
exit(errno);
}
return 0;
}