recv来自服务器的传入流量

Question

我有以下功能设置,每2分钟从服务器接收数据.我第一次调用函数它似乎工作,但然后它冻结在recv永远不会返回的调用.我是否需要在每次调用时分配缓冲区,即使服务器没有任何内容可以发送？

#define RCVBUFSIZE 32

void Receive()
{   
    UINT totalBytesRcvd = 0, bytesRcvd = 0;
    char buffer[RCVBUFSIZE];     /* Buffer for string */

    /* Receive up to the buffer size (minus 1 to leave space for 
    a null terminator) bytes from the sender */

    bytesRcvd = recv(sockClient, buffer, RCVBUFSIZE - 1, 0);

    if (bytesRcvd)
    {
        buffer[bytesRcvd] = '\0';
        MessageBox(0, buffer, 0, 0); //some way to display the received buffer
    }
    else if (bytesRcvd == SOCKET_ERROR)
    {
        return;
    }
}

Answer 1

(1)你的缓冲区没有真正分配,它驻留在堆栈上.您通常不必担心在堆栈上使用32个字节.

(2)recv应该阻止,直到它有东西要接收.你可以通过使用非阻塞套接字或使用来解决这个问题select.请参阅此处以供参考.

特别是,你可以

(2a)使用ioctlsocket将套接字设置为非阻塞模式.然后,当你打电话read,没有什么可读,你会得到错误EWOULDBLOCK.

unsigned long non_blocking = 1;
ioctlsocket (sockClient, FIONBIO, &non_blocking);

然后读书变成了

bytesRcvd = recv(sockClient, buffer, RCVBUFSIZE - 1, 0);
if (bytesRcvd == -1) {
    if (WSAGetLastError() == EWOULDBLOCK) {
        // nothing to read now
    } else {
        // an actual error occurred
    }
} else {
    // reading was successful. Call to MsgBox here
}

(2b)或者,您可以在实际调用之前调用select以确定是否有要读取的数据read.

struct timeval timeout;
timeout.tv_usec = 0;
timeout.tv_sec = 0;

fd_set r;
FD_ZERO (&r);
FD_SET (sockClient, &r);
switch (select (sockClient + 1, &r, NULL, NULL, &timeout)) {
    case -1:
        // error
        break;
    case 0:
        // nothing to read
        break;
    case 1:
        // you may call read ()
        break;
}