Question

我的目标是编写C ++程序，使用udp协议从网络接收数据。 OS - linux。我几乎没有问题。

我想确保我可以使用linux C库来编写C ++程序。
是否有任何存在的完整教程，如何在linux中使用套接字编程一步一步地进行操作？（我知道网络中有很多教程，但我正在寻找能帮助我从INTERNET接收udp数据的东西，而不是同一设备上的其他程序。）。

我在终端（使用tcpdump）中看到我的计算机收到发往指定端口的udp包。我的程序有什么问题，看起来像这样

class Connection
{
private:
    char * buffer;
    int bufferSize;
    int sock;
    struct sockaddr_in server;
    struct sockaddr_in other;
    socklen_t addressLength;

public:
    Connection(string address, int port, int bufferSize);
    ~Connection();
    int reciveData();
};

Connection::Connection(string address, int port, int bufferSize)
{
    this->addressLength = sizeof(this->server);

    this->sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);

    if(this->sock == -1)
    {
        cout << "Socket error!" << endl;
        exit(1);
    }

    memset(&(this->server), 0, sizeof(this->server));
    this->server.sin_family = AF_INET;
    this->server.sin_port = htons(port);
    this->server.sin_addr.s_addr = htonl(INADDR_ANY);

    if( bind(this->sock, (sockaddr *) &(this->server), this->addressLength) == -1 )
    {
        cout << "Bind socket error!" << endl;
        exit(1);
    }

    this->bufferSize = bufferSize;
    this->buffer = new char[bufferSize];

    cout << "Socket created!" << endl;
}

int Connection::receiveData()
{
    int returned;
    fflush(stdout);

    if( (returned =recvfrom(this->sock, this->buffer, this->bufferSize, 0, (sockaddr *) &(this->other), &this->addressLength)) == -1)
    {
        cout << "Receiving error!" << endl;
        exit(1);
    }

    return returned;
}

当我打电话给receiveData()时没有发生任何事情 - 我认为程序会等待一些udp包（我不知道为什么他没有收到它）。

有人能解释一下udp服务器和客户端程序之间的区别吗？

非常感谢。

Answer 1

调用recvfrom()时，您将向其传递指向this->addressLength的指针。在输入时，长度需要是地址缓冲区的完整大小。输出时，返回实际的地址长度。因此recvfrom()可能会改变您的addressLength成员，从而影响后续代码。改为使用局部变量：

int Connection::receiveData()
{
    int returned;
    int addrlen = sizeof(this->other);

    fflush(stdout);

    returned = recvfrom(this->sock, this->buffer, this->bufferSize, 0, (sockaddr *) &(this->other), &addrLen);
    if( returned == -1 )
    {
        cout << "Receiving error!" << endl;
        exit(1);
    }

    return returned;
}

或者，改为使用单独的成员变量：

class Connection
{
private:
    char * buffer;
    int bufferSize;
    int sock;
    struct sockaddr_in server;
    struct sockaddr_in other;
    socklen_t serverAddressLength;
    socklen_t otherAddressLength;

public:
    Connection(string address, int port, int bufferSize);
    ~Connection();
    int reciveData();
};

Connection::Connection(string address, int port, int bufferSize)
{
    this->serverAddressLength = sizeof(this->server);

    this->sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);

    if(this->sock == -1)
    {
        cout << "Socket error!" << endl;
        exit(1);
    }

    if(this->sock == -1)
    {
        cout << "Socket error!" << endl;
        exit(1);
    }

    memset(&(this->server), 0, sizeof(this->server));
    this->server.sin_family = AF_INET;
    this->server.sin_port = htons(port);
    this->server.sin_addr.s_addr = htonl(INADDR_ANY);

    if( bind(this->sock, (sockaddr *) &(this->server), this->serverAddressLength) == -1 )
    {
        cout << "Bind socket error!" << endl;
        exit(1);
    }

    this->bufferSize = bufferSize;
    this->buffer = new char[bufferSize];

    cout << "Socket created!" << endl;
}

int Connection::receiveData()
{
    int returned;
    fflush(stdout);

    this->otherAddressLength = sizeof(this->other);
    if( (returned =recvfrom(this->sock, this->buffer, this->bufferSize, 0, (sockaddr *) &(this->other), &this->otherAddressLength)) == -1)
    {
        cout << "Receiving error!" << endl;
        exit(1);
    }

    return returned;
}

无法使用udp协议从网络接收数据

1 个答案: