服务器只接收来自客户端的空字符串?
问题描述:
所以我有一个基本的客户端/服务器C++程序。现在,当客户端连接到服务器时,我希望服务器发送“Hello,world”消息,并且客户端响应“Hello,server”,以确保我正确发送和解除消息。服务器只接收来自客户端的空字符串?
当我运行时,客户端收到来自服务器的消息,但服务器只收到来自客户端的空字符串。
下面是客户端
int main(int argc, char *argv[]) {
int sockfd, numbytes;
char buf[MAXDATASIZE];
struct addrinfo hints, *servinfo, *p;
int rv;
char s[INET6_ADDRSTRLEN];
if (argc != 2) {
fprintf(stderr,"usage: client hostname\n");
exit(1);
}
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if ((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and connect to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("client: socket");
continue;
}
if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
perror("client: connect");
continue;
}
break;
}
if (p == NULL) {
fprintf(stderr, "client: failed to connect\n");
return 2;
}
inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
s, sizeof s);
printf("client: connecting to %s\n", s);
freeaddrinfo(servinfo); // all done with this structure
if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {
perror("recv");
exit(1);
}
if (send(sockfd, "Hello, client!", 13, 0) == -1) {
perror("send");
}
buf[numbytes] = '\0';
printf("client: received '%s'\n",buf);
close(sockfd);
return 0;
}
代码,这里的服务器的代码
int main(void)
{
int sockfd, new_fd, numbytes; // listen on sock_fd, new connection on new_fd
char buf[MAXDATASIZE];
struct addrinfo hints, *servinfo, *p;
struct sockaddr_storage their_addr; // connector's address information
socklen_t sin_size;
struct sigaction sa;
int yes=1;
char s[INET6_ADDRSTRLEN];
int rv;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // use my IP
if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("server: socket");
continue;
}
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
perror("server: bind");
continue;
}
break;
}
freeaddrinfo(servinfo); // all done with this structure
if (p == NULL) {
fprintf(stderr, "server: failed to bind\n");
exit(1);
}
if (listen(sockfd, BACKLOG) == -1) {
perror("listen");
exit(1);
}
sa.sa_handler = sigchld_handler; // reap all dead processes
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) == -1) {
perror("sigaction");
exit(1);
}
printf("server: waiting for connections...\n");
while(1) { // main accept() loop
sin_size = sizeof their_addr;
new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
if (new_fd == -1) {
perror("accept");
continue;
}
inet_ntop(their_addr.ss_family,
get_in_addr((struct sockaddr *)&their_addr),
s, sizeof s);
printf("server: got connection from %s\n", s);
if (!fork()) { // this is the child process
close(sockfd); // child doesn't need the listener
if (send(new_fd, "Hello, world!", 13, 0) == -1)
perror("send");
if (numbytes = recv(new_fd, &buf, MAXDATASIZE-1, 0) == -1) {
perror("recv");
exit(1);
}
buf[numbytes] = '\0';
printf("server: received '%s'\n",buf);
close(new_fd);
exit(0);
}
close(new_fd); // parent doesn't need this
}
return 0;
}
答
现在我想通了:
if (numbytes = recv(new_fd, &buf, MAXDATASIZE-1, 0) == -1) {
recv(new_fd, &buf, MAXDATASIZE-1, 0) == -1
是0成功1出错。那被分配到numbytes
。所以,你要添加parenthesises这样的:
if ((numbytes = recv(new_fd, &buf, MAXDATASIZE-1, 0)) == -1) {
或者你想把它分成两行是这样的:
numbytes = recv(new_fd, &buf, MAXDATASIZE-1, 0);
if (numbytes == -1) {
哦,下次PLZ决定用C或C++,无论是不同的语言。
SO不是调试服务。我想这就是为什么这个问题被降低了。我看了看,也没有立即发现问题。 –
@ Doug0855在没有任何调试工作和观察的具体证据的情况下转储一堆代码是非常有用的。谢谢。 –
谢谢你让我知道我的问题为什么不好,现在我知道了(对这个社区很抱歉)。另外,谢谢你,我现在正在工作,是个笨蛋 – Doug0855