服務器只接收來自客戶端的空字符串？

Question

所以我有一個基本的客戶端/服務器C++程序。現在，當客戶端連接到服務器時，我希望服務器發送「Hello，world」消息，並且客戶端響應「Hello，server」，以確保我正確發送和解除消息。

當我運行時，客戶端收到來自服務器的消息，但服務器只收到來自客戶端的空字符串。

下面是客戶端

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; 
} 

代碼，這裏的服務器的代碼

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; 
} 

Answer 1

現在我想通了：

if (numbytes = recv(new_fd, &buf, MAXDATASIZE-1, 0) == -1) { 

recv(new_fd, &buf, MAXDATASIZE-1, 0) == -1是0成功1出錯。那被分配到numbytes。所以，你要添加parenthesises這樣的：

if ((numbytes = recv(new_fd, &buf, MAXDATASIZE-1, 0)) == -1) { 

或者你想把它分成兩行是這樣的：

numbytes = recv(new_fd, &buf, MAXDATASIZE-1, 0); 
if (numbytes == -1) { 

哦，下次PLZ決定用C或C++，無論是不同的語言。