我正在尝试使用UDP编写客户端服务器程序,并使用等待和停止,但我还没有到达那个部分,我仍在努力弄清楚两个进程(服务器和客户端)如何通信,因为在我的客户端程序中,用户需要输入服务器名称或IP地址以及端口名称,然后发送一个表达式,服务器应该计算。然而,我在互联网上找到了一些教程,并按照所述进行编码,但我无法使客户端与服务器通信。以下是我的代码,请告诉我我做错了什么,如果是
客户端代码:
服务器程序不输出任何内容,而客户端则一直输出,直到进程被中断:
我尝试将服务器名称更改为localhost,以及其他端口,但都没有成功。
bind()
、sendto()
、recvfrom()
或socket()
,或者全部都是。我看不出到底哪里出了问题。我知道客户端不应该在一个无限循环中运行,但目前我想让程序彼此通信,之后我会优化我的代码。谢谢!客户端代码:
#include <stdio.h> // Default System Calls
#include <stdlib.h> // Needed for OS X
#include <string.h> // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h> // To control the timeout mechanism
#define EXPR_SIZE 1024
#define BUFLEN 512
#define TRUE 1
#define FALSE 0
#define SERVERLEN 1024
int main(int argc, char **argv){
long portNum; // Since it's possible to input a value bigger
// than 65535 we'll be using long to
// avoid overflows
char expr[EXPR_SIZE];
char server[SERVERLEN];
int fd; // file descriptor for the connected socket
int buf[512];
struct hostent *h; // information of the host
unsigned int addrLen; // address length after getting the port number
struct sockaddr_in myaddr; // address of the client
struct sockaddr_in servaddr; // server's address
unsigned int exprLen;
socklen_t slen = sizeof(servaddr);
printf("Enter server name or IP address:");
scanf("%s",server);
printf("Enter port:");
scanf("%ld",&portNum);
if ((portNum < 0) || (portNum > 65535)) {
printf("Invalid port number. Terminating.");
return 0;
}
printf("Enter expression:");
scanf("%s",expr);
if((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
perror("cannot create socket");
return 0;
}
memset((char *)&myaddr, 0, sizeof(myaddr));
myaddr.sin_family = AF_INET;
myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
myaddr.sin_port = htons(0);
if(bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0){
perror("cannot bind");
return 0;
}
/*
// Discovering the port number the OS allocated
addrLen = sizeof(myaddr);
if(getsockname(fd, (struct sockaddr *)&myaddr, &addrLen) < 0){
perror("cannot getsockname");
return 0;
}
printf("local port number = %d\n", ntohs(myaddr.sin_port));
*/
memset((char*)&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htonl(portNum);
exprLen = sizeof(expr);
while(TRUE){
printf("Sending message to %s port %ld\n",server, portNum);
if (sendto(fd, expr, strlen(expr), 0, (struct sockaddr *)&servaddr, slen) < 0) {
perror("cannot sendto()");
}
printf("Success\n");
}
return 0;
}
服务器端代码:
#include <stdio.h> // Default System Calls
#include <stdlib.h> // Needed for OS X
#include <string.h> // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h> // To control the timeout mechanism
#define EXPR_SIZE 1024
#define BUFLEN 512
#define TRUE 1
#define SERVERLEN 1024
int main(int argc, char **argv){
struct sockaddr_in myaddr; // address of the server
struct sockaddr_in claddr; // address of the client
char buf[BUFLEN];
int fd;
long recvlen;
socklen_t clientlen;
if((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
perror("cannot create socket");
return 0;
}
memset((char *)&myaddr, 0, sizeof(myaddr));
myaddr.sin_family = AF_INET;
myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
myaddr.sin_port = htons(0);
if(bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0){
perror("cannot bind");
return 0;
}
clientlen = sizeof(claddr);
while (TRUE) {
recvlen = recvfrom(fd, buf, BUFLEN, 0, (struct sockaddr *)&claddr, &clientlen);
if (recvlen < 0) {
perror("cannot recvfrom()");
return 0;
}
printf("Received %ld bytes\n",recvlen);
buf[recvlen] = 0;
printf("Received message: \"%s\"\n",buf);
}
return 0;
}
服务器程序不输出任何内容,而客户端则一直输出,直到进程被中断:
Enter server name or IP address:127.0.0.1
Enter port:30
Enter expression:2+2
Sending message to 127.0.0.1 port 30
cannot sendto(): Can't assign requested address
我尝试将服务器名称更改为localhost,以及其他端口,但都没有成功。
scanf("%s",server);
,在%s
格式说明符上没有最大输入字符修饰符。因此用户可以越过输入缓冲区,导致未定义的行为并可能导致段错误事件。建议修改为:scanf("%1023s",server);
。 - user3629249int main(void)
。 - user3629249scanf()
,始终检查返回的值(而不是参数值),以确保操作成功。 - user3629249