How can I stop C MEX s-function from outputting anything?

I have a C MEX s-function that receives some data, processes it and outputs an array.

I was wondering if there is a way to not output anything (instead of zeros) when the s-function does not receive anything. Inside the s-function I can detect whether anything has been received but I couldn't figure out a way to use this information to inhibit the output (e.g. show nothing when connected to a Display (sink)).

TIA,

Answer 1

[Sunny Talekar]

I managed to achieve the desired outcome by configuring the s-function output as variable-size mode and set the current output dimension to 0 when there is nothing to output.

Answer 2

[Abhi Sundararaman]

It shouldn't be possible to remove the output entirely, since if there is an outport on your s-function block, there will always be an output signal.

However, if you want a visual indicator of the output being invalid (basically the same as outputting nothing), you could try outputting "NaN" instead of zeros.

[Sunny Talekar]

The s-function is designed to output an array of uint8s. I tried setting it to NaN, as suggested, using mxGetNaN(), NAN, std::nan but the output either gets limited to 255 or 0. Not sure, if I'm doing it right.