Matlab UDP Recieve Error

2016 10 31
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更新时间：2016 10 31
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Hi,
I'm running FlightGear simulation software and output some variable data through UDP on the loopback address 127.0.0.1, port 1234. Using the SocketTest application I can see the data being received however I would like to do this through Matlab which is running on the same PC.
I've read through the following example: https://uk.mathworks.com/matlabcentral/answers/10234-recieving-udp-from-iphone
I try to run the following:
while(1)
u = udp('localhost',1234,'localport',1234);
u.InputBufferSize = 1000;
u.DatagramReceivedFcn = @localReadDatagram;
fopen(u);
end
My issue is that I always get the error: "Unsuccessful open: Address already in use: Cannot bind ", can anyone help?
Thanks, Joe

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Walter Roberson
Walter Roberson 2016-10-31

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You should probably use a different localport unless the receiving software insists that the transmitting port be 1234 . localport is the port number that data is transmitted from.

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Joe Fleming
Joe Fleming 2016-10-31
编辑：Joe Fleming 2016-10-31
Ok so changing the Flightgear port to 5000 and then changing my Matlab code to:
while(1)
u = udp('localhost',5001,'localport',5000);
u.InputBufferSize = 1000;
u.DatagramReceivedFcn = @localReadDatagram;
fopen(u);
end
I now get the following error:
Error using icinterface/fopen (line 83)
Unsuccessful open: Address already in use: Cannot bind
Error in UDP_Connection (line 6)
fopen(u);
Undefined function or variable 'localReadDatagram'.
Error in instrcb (line 36)
feval(val{1}, obj, eventStruct, val{2:end});
Warning: The DatagramReceivedFcn is being disabled. To enable the callback property
either connect to the hardware with FOPEN or set the DatagramReceivedFcn property.
Walter Roberson
Walter Roberson 2016-10-31
Ah, the problem is that you are doing the open in a loop. You should only open once, and then make sure that u does not go out of scope while you use it. Remember to close it after you are done.
Joe Fleming
Joe Fleming 2016-10-31
Ok so I've removed the code from a while loop and I'll just close it through the command window manually for now. Socket test shows the address as 127.0.0.1:52867, so I've set the the ports to the following, is that correct?
u = udp('localhost',52867,'localport',5000);
u.InputBufferSize = 1000;
u.DatagramReceivedFcn = @localReadDatagram;
fopen(u);
I now get the error:
Undefined function or variable 'localReadDatagram'.
Error in instrcb (line 36)
feval(val{1}, obj, eventStruct, val{2:end});
Joe Fleming
Joe Fleming 2016-10-31
All sorted - Thanks for your help

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