qt QtUdpSocket

Today’s basic job is to watch over a machine and doing basic communication.

How to watch over if the machine is online?
Basic Idea: Because we are transferring Datagrams, so use QSocket.hasPendingDataGrams(). However the socket states changes very quickly, so use a for-loop to ‘wait’ until a datagram is received and if so, return true.
How to auto-find the IP? Use multicast socket, then record the ip addr when recvdatagram() is called.

My_socket->bind(QHostAddress::AnyIPv4, m_LimitMPort,QUdpSocket::ShareAddress | QUdpSocket::ReuseAddressHint)// return true if succesful
My_socket-> joinMulticastGroup(QHostAddress("224.224.224.224"))

How to transfer my own defined structure?
Cause I have defined a structure for data, I need to cast it to char* as this is qt pre-written function in writedatagram method call.
Solution: use memcpy to copy my data into a char*, such as

int size = sizeof(My_struct1) + sizeof(My_struct2);
char* buffer[size] = 0;
memcpy(buffer, &transfer1, sizeof(My_struct1));
memcpy(buffer + sizeof(transfer1), &transfer2, sizeof(My_struct2));

Remember always do the pointer bias.
This also works when I have to parse a received bytes Array to my own defined struct.

*recorded_ = *((My_struct *)(m_BytesArray))// Firstly I cast the pointer type then I give the value to recorded, or the value get wasted.

Always use mutex when operating on the data queue or vector,
connect(socket, SIGNAL, Qobject, SLOT) means socket would operate SLOT when a SIGNAL is emitted and caught. It’s like abstract version of click the button and perform an action. (OnButtonClicked())

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