带有BSD套接字的错误文件描述符

Question

当我尝试从我的tcp服务器向我的tcp客户端发送数据时，我总是收到“Bad file descriptor”错误。这对套接字来说意味着什么？我现在已经呆了一段时间了，我不知道我的代码有什么问题。它基本上和我前两天使用的代码基本相同，代码工作正常。我希望有人能告诉我什么是错误的文件描述符尝试通过套接字发送时的常见原因，以及如何检查/修复它们。任何帮助表示赞赏。我会在下面发布一些代码以防万一。

/*Waits to connect a client. Returns true if successful*/ 
bool TcpServer::launchServer() { 
int status; 

struct addrinfo hints; 
struct addrinfo *servinfo; //will point to the results 

//store the connecting address and size 
struct sockaddr_storage their_addr; 
socklen_t their_addr_size; 


memset(&hints, 0, sizeof hints); //make sure the struct is empty 
hints.ai_family = AF_INET; //ipv4 
hints.ai_socktype = SOCK_STREAM; //tcp 

//get server info, put into servinfo 
if ((status = getaddrinfo("192.168.2.3", port, &hints, &servinfo)) != 0) { 
    printf("\ngetaddrinfo error: %m", errno); 
    return false; 
} 

//make socket 
fd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol); 
if (fd < 0) { 
    printf("\nserver socket failure %m", errno); 
    return false; 
} 

//allow reuse of port 
int yes=1; 
if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,(char*) &yes,sizeof(int)) == -1) { 
    perror("setsockopt"); 
    return false; 
} 

//bind 
if(bind (fd, servinfo->ai_addr, servinfo->ai_addrlen) < 0) { 
    printf("\nBind error %m", errno); 
    return false; 
} 

//free up space 
freeaddrinfo(servinfo); 

//listen 
if(listen(fd, 5) < 0) { 
    printf("\nListen error %m", errno); 
    return false; 
} 
their_addr_size = sizeof(their_addr); 


//accept 
comm_fd = accept(fd, (struct sockaddr*)&their_addr, &their_addr_size); 
if(comm_fd < 0) { 
    printf("\nAccept error %m", errno); 
    return false; 
} 

return true; 
} //END LAUNCHSERVER 






void TcpServer::communicate() { 


fd_set read_flags,write_flags; // the flag sets to be used 
struct timeval waitd = {10, 0};   // the max wait time for an event 
int sel;  // holds return value for select(); 
int numRead; //holds return value for read() 
int numSent; //holds return value for send() 
char in[255]; //in buffer 
char out[255]; //out buffer 

//clear buffersz 
memset(&in, 0, 255); 
memset(&out, 0, 255); 


while(!done) { 
    FD_ZERO(&read_flags); 
    FD_ZERO(&write_flags); 
    FD_SET(comm_fd, &read_flags); 
    FD_SET(comm_fd, &write_flags); 
    FD_SET(STDIN_FILENO, &read_flags); 
    FD_SET(STDIN_FILENO, &write_flags); 

    //call select 
    sel = select(comm_fd+1, &read_flags, &write_flags, (fd_set*)0, &waitd); 

    //if an error with select 
    if(sel < 0) 
     continue; 

    //if socket ready for reading 
    if(FD_ISSET(comm_fd, &read_flags)) { 

     //clear set 
     FD_CLR(comm_fd, &read_flags); 

     memset(&in, 0, 255); 

     numRead = recv(comm_fd, in, 255, 0); 
     //if an error, exit 
     if(numRead < 0) { 
      printf("\nError reading %m", errno); 
      myAgent->getRobot()->pauseSensorStream(); 
      done = true; 
     } //end if error 
     //if connection closed, exit 
     else if(numRead == 0) { 
      printf("\nClosing socket"); 
      close(comm_fd); 
      done = true; 
     } //end if connection closed 
     //if message, call getsendback 
     else if(in[0] != '\0') { 
      //std::cout<<"\nClient: "<<in; 
      getSendBack(in); 
     } //end if message 
    } //end if ready for read 


    //if stdin is ready for reading 
    if(FD_ISSET(STDIN_FILENO, &read_flags)) 
     fgets(out, 255, stdin); 


    //if socket ready for writing 
    if(FD_ISSET(comm_fd, &write_flags)) { 

     //printf("\nSocket ready for write"); 
     FD_CLR(comm_fd, &write_flags); 

     //check validity by checking for a digit 
     if(isdigit(out[0])) { 

      //create message to send 
      std::stringstream tosend; 
      tosend<<"@ "<<out; 
      //std::cout<<"\ntosend: "<<tosend.str(); 

      //send 
      //********ERROR HAPPENS HERE PRINTS OUT MESSAGE BELOW****** 
      numSent = send(comm_fd, tosend.str().c_str(), tosend.str().length(), 0); 
     } //end if valid message 
     //if error, exit 
     if(numSent < 0) { 
      printf("\nError sending %m", errno); 
      done = true; 
     } //end if error 
     //wait for message to get there, then clear 
     usleep(5000); 
     memset(&out, 0, 255); 
    } //end if 
} //end while 
} //END COMMUNICATE 

客户端代码基本相同。

Answer 1

你回答了你自己的问题。如果没有明确地初始化numSent和numRead，你会得到垃圾，这可能是numSent的负数，如果out []数组中没有数字，会导致错误。

Answer 2

当errno是EBADF时，您的程序会打印“错误的文件描述符”。 从手册页发送：

EBADF =一个无效的描述符被指定。

我很确定socket在send（）调用之前是关闭的。 这可能发生，因为程序可以在“连接关闭”分支后进入“准备写入”分支。

尝试以下操作：

else if(numRead == 0) { 
    printf("\nClosing socket"); 
    close(comm_fd); 
    break; 
} 

相反的：

else if(numRead == 0) { 
     printf("\nClosing socket"); 
     close(comm_fd); 
     done = true; 
    }