Can someone please explain this section of code

Questions » Can someone please explain this section of code

Joe Danlloh

6 years, 9 months ago.

EthernetInterface eth;
TCPSocketConnection socket;
 
typedef struct packetToSent_s {
uint16_t data[80]; 
} packetToSend_t;
 
packetToSend_t dataOut;
 
int main()
{
    eth.init("192.168.1.4","255.255.255.0","192.168.1.1");  // Static IP of 192.168.1.4
    eth.connect();
 
    socket.connect("192.168.1.5", 1001)  // connect to the PC at the given IP address and socket 
 
 
    socket.send_all((char*)&dataOut,sizeof(packetToSend_t)); // send the data
}

Retrieved from https://developer.mbed.org/questions/5238/Ethernet-for-high-speed-data-transfer-NO/ credit to Andy A.

Where do I define the data that I want to send from my mbed to the server? I'm trying to define dataOut since socket.send_all function sends the data contained in the address of dataOut pointed to.. yet I get compilation errors.

Please help.

Hi Joe, in order to assist you better can you please edit your post and place "<<code>> <</code>>" tags around your code excerpt? Thanks!

posted by Jenny Plunkett 11 Jul 2017

Thank you Jenny did not know that was how to do it.

posted by Joe Danlloh 11 Jul 2017

I'm also having an issue when using DHCP that the eth.getIPAddress() function is not printing anything to my terminal, just appears blank and then continues to run the code

posted by Joe Danlloh 11 Jul 2017

1 Answer

Andy A

6 years, 9 months ago.

Here's a more annotated version of the code. This was originally posted as a basic framework to get data sent rather than a full working application.

Also keep in mind this is mbed2 code, mbed5 changes some of the function calls slightly.

// the ethernet and socket objects
EthernetInterface eth;
TCPSocketConnection socket;
 
// A data structure of the data to send
// In this case it's fairly pointless, you may as well just use a uint16_t[] directly in place of this
// But if you package what you want into a structure then you don't need to change the 
// transmission code if you change what is being sent, you just change the structure definition.
typedef struct packetToSent_s {
uint16_t data[80]; 
} packetToSend_t;

// an instance of the packet to send.
packetToSend_t dataOut;
 
int main()
{
   // initialize the ethernet interface to a static IP address
    eth.init("192.168.1.4","255.255.255.0","192.168.1.1");  // Static IP of 192.168.1.4

   // connect. Ideally you should check at this point that the connect succeeded.
    eth.connect();
 
   // open a network socket. to port 1001 on IP address 192.168.1.5
   // it is assumed that a TCP server is listening for connections on that address/port
    socket.connect("192.168.1.5", 1001) 
  
   // at this point you should really check that the socket opened OK. 
 
   // you should now set the data to send. e.g.
   for (int i=0;i<80;i++)
     dataOut.data[i]=i*5;

   // send the data packet.
    socket.send_all((char*)&dataOut,sizeof(packetToSend_t));

   // ideally we should also check the return value from send_all to verify that there weren't any errors.
}

Accepted Answer

Thanks so much Andy. It's the struct part that I didn't quite understand. You've clarified perfectly.