CODEWITHSUNDEEP
cmatlabmex
marcusagren
marcusagren

Reputation: 1

MEX (C -> Matlab) converting to int -> double different on mac/linux and windows

I have a Matlab script that calls a C code which reads my dat file consisting of all my data which of one is the timestamp_low. Running my script on windows I get the correct time value of 4.1472*10^9 but of linux/mac I get the value 1.8447*10^19. Essentially I'm only reading from the file and saving it.

unsigned int timestamp_low = inBytes[0] + (inBytes[1] << 8) +
    (inBytes[2] << 16) + (inBytes[3] << 24);
mxSetField(outCell, 0, "timestamp_low", mxCreateDoubleScalar((double)timestamp_low));

Does anyone know if the mex-compiler works differently on different OS for this kind of stuff? I haven't written this code myself, so I'm not super familiar with details. I use it to gather CSI from a WiFi device. I've tried on different Matlab versions and on Mac/Linux and they produce the same (wrong) value.

Upvotes: 0

Views: 65

Answers (1)

Paul R
Paul R

Reputation: 212969

I suspect you have some Undefined Behaviour here:

unsigned int timestamp_low = inBytes[0] + (inBytes[1] << 8) +
                            (inBytes[2] << 16) + (inBytes[3] << 24);

(although it's not clear as you haven't told us the type of inBytes).

Try:

unsigned int timestamp_low = (unsigned int)inBytes[0] + ((unsigned int)inBytes[1] << 8) + 
                            ((unsigned int)inBytes[2] << 16) + ((unsigned int)inBytes[3] << 24);

Upvotes: 1

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