Problem to bind a UDP socket.

[jenya7]

The bind method

int UDP::Start(QString local_ip, quint16 local_port)
{
    int result;

    //socket->reset();
    //socket->setProxy(QNetworkProxy::NoProxy);
        
    //result = socket->bind(QHostAddress::Any, local_port);
    result = socket->bind(QHostAddress(local_ip), local_port);

    QString err = socket->errorString();

    result = socket->error();

    return result;
}

In main

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    UDP udp_1 ;

    int soc_err;
    QString qs;

    QObject::connect(&udp_1, &UDP::ReadyForReader, &reader, &READER::ReadyForReader);
  
    GetNetInfo();

    soc_err = udp_1.Start("192.68.3.40", 8001);

    if (soc_err)
    {
        qs = QString::number(soc_err);
        cout << "Socket 1 error - " << qs.toStdString() << std::endl;
    }
    else
    {
        cout << "Socket 1 OK\n";
    }

    return a.exec();
}

I see in console
192.168.3.40
172.16.1.118
127.0.0.1
Socket 1 error - -1

It sees the IP - 192.168.3.40 but I get an error. Why?

[Christian Ehrlicher]

@jenya7 said in Problem to bind a UDP socket.:

"192.68.3.40"

Typo?

[jenya7]

@Christian-Ehrlicher said in Problem to bind a UDP socket.:

@jenya7 said in Problem to bind a UDP socket.:

"192.68.3.40"

Typo?

yes. it's "192.168.3.40"

[Christian Ehrlicher]

So does it work now? If so please print out the errorString.

[jenya7]

@Christian-Ehrlicher said in Problem to bind a UDP socket.:

So does it work now? If so please print out the errorString.

to print it I added another argument

soc_err = udp_1.Start("192.168.3.40", 8001, &err_str);

    if (soc_err)
    {
        qs = QString::number(soc_err);
        cout << "Socket 1 error - " << qs.toStdString() << std::endl;
        cout << err_str.toStdString();
    }
    else
    {
        cout << "Socket 1 OK\n";
    }

It prints
192.168.3.40
172.16.1.118
127.0.0.1
Socket 1 error - -1
Unknown error

this way

result = socket->bind(QHostAddress::Any, local_port);

I also get
Socket 1 error - -1
Unknown error

[Christian Ehrlicher]

@jenya7 said in Problem to bind a UDP socket.:

172.16.1.118
127.0.0.1

Where do those two IPs come from? Please post your actual code and the real output. Also make sure the IPs you're using are correct (= your host has those IPs assigned)

[jenya7]

@Christian-Ehrlicher said in Problem to bind a UDP socket.:

@jenya7 said in Problem to bind a UDP socket.:

172.16.1.118
127.0.0.1

Where do those two IPs come from? Please post your actual code and the real output. Also make sure the IPs you're using are correct (= your host has those IPs assigned)

172.16.1.118 - is another network card. 127.0.0.1 - default local host.

I changed for PC with only one network card.
cmd->ipconfig
Ethernet adapter Local Area Connection 2:

Connection-specific DNS Suffix . :
Link-local IPv6 Address . . . . . : fe80::7d2a:547e:e90a:6e3e%12
IPv4 Address. . . . . . . . . . . : 172.16.1.139
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 172.16.1.1

soc_err = udp_1.Start("172.16.1.139", 8001, &err_str);

I get
172.16.1.139
127.0.0.1
Socket 1 error - -1
Unknown error

[KroMignon]

@jenya7 said in Problem to bind a UDP socket.:

result = socket->bind(QHostAddress(local_ip), local_port);
QString err = socket->errorString();
result = socket->error();

This code do not make sense to me, you have to check if operation was not successful before trying to find an error!
There is no error code "Success" in QAbstractSocket::SocketError (cf. https://doc.qt.io/qt-5/qabstractsocket.html#SocketError-enum).

Please review your code.

[jsulm]

@jenya7 Please connect a slot to https://doc.qt.io/qt-5/qabstractsocket.html#errorOccurred and print the error there.

[jenya7]

@KroMignon said in Problem to bind a UDP socket.:

@jenya7 said in Problem to bind a UDP socket.:

result = socket->bind(QHostAddress(local_ip), local_port);
QString err = socket->errorString();
result = socket->error();

This code do not make sense to me, you have to check if operation was not successful before trying to find an error!
There is no error code "Success" in QAbstractSocket::SocketError (cf. https://doc.qt.io/qt-5/qabstractsocket.html#SocketError-enum).

Please review your code.

OK.

int UDP::Start(QString local_ip, quint16 local_port, QString *err_str)
{
    int result;

    //socket->reset();
    //socket->setProxy(QNetworkProxy::NoProxy);

    result = socket->bind(QHostAddress::Any, local_port);
    //result = socket->bind(QHostAddress(local_ip), local_port);

    if (result != 0)
    {
        *err_str = socket->errorString();
         result = socket->error();
    }

    return result;
}

So I get result = 1 after result = socket->bind(QHostAddress::Any, local_port);
Should I trust to a returned result?

[jenya7]

@jsulm said in Problem to bind a UDP socket.:

@jenya7 Please connect a slot to https://doc.qt.io/qt-5/qabstractsocket.html#errorOccurred and print the error there.

can not do that.
it's UDP socket, not Abstract socket. it has no errorOccurred signal.

QUdpSocket *socket;

[KroMignon]

@jenya7 said in Problem to bind a UDP socket.:

So I get result = 1 after result = socket->bind(QHostAddress::Any, local_port);
Should I trust to a returned result?

Please take time to read a little bit of documentation. This will save you many of your time. It is very easy with Qt Creator, you only have to hit F1 to get help for a function!

QUdpSocket::bind() (cf. https://doc.qt.io/qt-5/qabstractsocket.html#bind) will return a boolean:

• true: success
• false: error

[Christian Ehrlicher]

@jenya7 said in Problem to bind a UDP socket.:

it's UDP socket, not Abstract socket.

QUdpSocket derives from QAbstractSocket...

udp_1.Start("192.168.3.40", 8001, &err_str);

You call Start() with an IP which you computer doesn't have according your ipconfig output above. This can't work. Also 172.16.1.118 is not your IP.

[KroMignon]

@jenya7 said in Problem to bind a UDP socket.:

it's UDP socket, not Abstract socket. it has no errorOccurred signal.

QUpdSocket is based on QAbstractSocket, do you have C++ knowledge?
Do you know what subclassing means?

[jenya7]

@KroMignon said in Problem to bind a UDP socket.:

@jenya7 said in Problem to bind a UDP socket.:

it's UDP socket, not Abstract socket. it has no errorOccurred signal.

QUpdSocket is based on QAbstractSocket, do you have C++ knowledge?
Do you know what subclassing means?

QObject::connect(socket, &QAbstractSocket::error, this, &UDP::SocketError);

void UDP::SocketError(QAbstractSocket::SocketError socketError)
{
    qDebug() << "Socket Error: " << socketError;
}

I get
error: no matching member function for call to 'connect'

[Christian Ehrlicher]

@jenya7 said in Problem to bind a UDP socket.:

QObject::connect(socket, &QAbstractSocket::error, this, &UDP::SocketError);

And again to lazy to hit 'F1': https://doc.qt.io/qt-5/qabstractsocket-obsolete.html#error-1

Note: Signal error is overloaded in this class. To connect to this signal by using the function pointer syntax, Qt provides a convenient helper for obtaining the function pointer as shown in this example:

connect(abstractSocket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error),
    [=](QAbstractSocket::SocketError socketError){ /* ... */ });

Also this signal is deprecated - use errorOccurred() if possible (since Qt5.15)

[KroMignon]

@jenya7 said in Problem to bind a UDP socket.:

QObject::connect(socket, &QAbstractSocket::error, this, &UDP::SocketError);

This signal is called errorOccurred() and not error()

[EDIT] errorOccurred() has been added with Qt 5.15, if you are using an older Qt version, use code suggested by @Christian-Ehrlicher

[jenya7]

@KroMignon said in Problem to bind a UDP socket.:

@jenya7 said in Problem to bind a UDP socket.:

So I get result = 1 after result = socket->bind(QHostAddress::Any, local_port);
Should I trust to a returned result?

Please take time to read a little bit of documentation. This will save you many of your time. It is very easy with Qt Creator, you only have to hit F1 to get help for a function!

QUdpSocket::bind() (cf. https://doc.qt.io/qt-5/qabstractsocket.html#bind) will return a boolean:

• true: success
• false: error

oops. sorry.