简单FTP客户端c++

我试图在C/c++中创建一个简单的FTP客户端，这将做简单的操作(连接，检索文件)。我到目前为止所做的工作是连接和登录。我使用套接字连接到端口21，就像任何常规FTP客户端一样。我遇到的问题是连接到输入命令PASV时指定的端口。我获得消息，解析它，然后在输入PASV时从重播消息计算端口。

227 Entering Passive Mode (a1, a2, a3, a4, p1, p2) 
DataPort = (p1 * 256) + p2

一旦我有了端口，我尝试创建另一个套接字并以同样的方式连接到它。这就是我的问题所在。到目前为止，我的代码张贴在下面。我不知道是否需要以同样的方式获得服务器地址。我没有从服务器得到响应(如果我实际上应该得到一个，我不知道)请提出任何问题或疑虑，谢谢。

const int FTP_PORT = 21;        // Server Port
const int SIZE = 1024;          // Size of Buffers
char receiveBuff[SIZE];         // Buffer to send to the server
char sendBuff[SIZE];            // Buffer to receive from server
char pasvBuff[] = "pasv";       // Buffer to see if PASV Command was entered
char quitBuff[] = "QUIT";       // Buffer to see if QUIT Command was entered
char pasvMessage[100];          // String for PASV information
int main(int argc, char *argv[])
{
    int length = 0, i=0;
    int a1, a2, a3, a4, p1, p2, dataPort;       //PASV Information
    /* Get Server Name from User */
    if (argc != 2)
    {
        cerr << "Usage: " << argv[0] << " server" << endl;
        return 1;
    }
    /* Obtain Host (Server) Info  */
    struct hostent *host;
    host = gethostbyname(argv[1]);
    if (host == (struct hostent *)NULL)
    {
        perror("Client: gethostbyname");
        return 2;
    }
    /* Add Server Information */
    struct sockaddr_in servAdr;             // Internet address of server
    memset(&servAdr, 0, sizeof(servAdr));   // Clear structure
    servAdr.sin_family = AF_INET;           // Set address typedef
    memcpy(&servAdr.sin_addr, host->h_addr, host->h_length);
    servAdr.sin_port = htons(FTP_PORT);     // Use FTP port
    /* Create Socket to Connect to FTP Server */
    int origSock;                   // Original socket in client
    if ((origSock = socket(PF_INET, SOCK_STREAM, 0)) < 0)
    {
        perror("Client: generate error");
        return 3;
    }
    /* Connect to FTP Server on Port 21 */
    if (connect(origSock, (struct sockaddr *)&servAdr, sizeof(servAdr)) < 0)
    {
        perror("Client: connect error");
        return 4;
    }
    /* Get Conenct Message and Print to Screen */
    read(origSock, receiveBuff, sizeof(receiveBuff) - 1);
    write(fileno(stdout), receiveBuff, sizeof(receiveBuff) - 1);
    do
    {
        /* Clear Buffers */
        memset(receiveBuff, 0, SIZE);
        memset(sendBuff, 0, SIZE);
        write(fileno(stdout), "Please enter a FTP Command: ", 28);      // Write User Interface
        read(fileno(stdin), sendBuff, SIZE);                            // Read Command from User
        send(origSock, sendBuff, strlen(sendBuff) , 0);                 // Send Command to Server
        read(origSock, receiveBuff, sizeof(receiveBuff) - 1);           // Read Response from Server
        write(fileno(stdout), receiveBuff, sizeof(receiveBuff) - 1);    // Print Response from Server to screen
        /* If PASV Command was Entered */
        if (strncmp(sendBuff, pasvBuff, 4) == 0)
        {
            sscanf(receiveBuff, "227 Entering Passive Mode (%d,%d,%d,%d,%d,%d)", &a1,&a2,&a3,&a4,&p1,&p2);
            dataPort = (p1 * 256) + p2;
            struct sockaddr_in servAdr2;                // Internet address of server
            memset(&servAdr2, 0, sizeof(servAdr2));     // Clear structure
            servAdr2.sin_family = AF_INET;              // Set address typedef
            memcpy(&servAdr2.sin_addr, host->h_addr, host->h_length);
            servAdr.sin_port = htons(dataPort);         // Use FTP port
            /* Create Socket to Connect to FTP Server */
            int dataSock;                               // Data socket in client
            if ((dataSock = socket(PF_INET, SOCK_STREAM, 0)) < 0)
            {
                perror("Client: generate error");
                return 3;
            }
            /* Connect to FTP Server on Data Port */
            if (connect(dataSock, (struct sockaddr *)&servAdr, sizeof(servAdr)) < 0)
            {
                perror("Client: connect error");
                return 4;
            }
            read(dataSock, receiveBuff, sizeof(receiveBuff) - 1);
            write(fileno(stdout), receiveBuff, sizeof(receiveBuff) - 1);
        }
    } while (strncmp(sendBuff, quitBuff, 4) != 0);      // Go until QUIT Command is entered
    close(origSock);
    return 0;
}