How to retrieve a BOOL type value returned from a .dll function

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Qian 2012-1-9

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Hi! I'm new to the external interface tools of MATLAB and I'm not very familiar with C/C++ so I was wondering if anyone here has experience.

I'm writing a control script for a near-infrared camera, which came with a driver .dll file and a brief description of the functions within it.

For example, I have a function described as:

BOOL DLL_Get_Spectra(double* pdblData, double* pdblCaseTemperature);

Description: Acquire one snapshot spectrum.

Parameter: double* pdblData: Pointer of spectrum power array allocated by the user (Buffer size >= pixel count)

double* pdblCaseTemperature: Pionter of case temperature.

Return value: Boolean TRUE: Operation completed FALSE: Operation failed

After loading dll and using libfunction, we see that the library is loaded without any problems:

[lib.pointer, doublePtr] DLL_Get_Wavelenth(double, doublePtr)

I have read how to pass pointers into MATLAB, but not much on how to read pointers from MATLAB, do I just use doublePtr.Value?

Also, MATLAB does not have a BOOL type, so how am I suppose to read the returned lib.pointer as TRUE or FALSE?

Thanks!

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Answer 1

Philip Borghesani 2012-1-10

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That function should not be returning a lib.pointer to MATLAB something went wrong loading the dll. What warnings were reported when loading the library?

BOOL is not a traditional c data type and should be returned to MATLAB as a simple number 0 for false and 1 for true. However a header file is frequently needed to define BOOL for a library. In this case I expect the library header expects windows.h to be included before it is used.

You can fix the header file by adding appropriate typedefs or includes. Or you can generate a prototype file and fix that using uint8 or logical as the data type.

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Qian 2012-1-11

Thanks Philip and Walter for continuing the follow-up on this thread.

I tried generating a prototype function (Spec2020Dll_proto.m) with #include <windows.h> in the original header as Philip had suggested.

When I used loadlibrary with the prototype file, no warnings were generated:

loadlibrary('Spec2020Dll.dll', @Spec2020Dll_proto)

>>

I used libfunctionview to verify that the function is indeed loaded:

[int32,doublePtr,doublePtr] DLL_Get_Spectra (doublePtr,doublePtr)

I can see now that the BOOL type is now in MATLAB corresponding to int32.

However, when I'm actually calling a function, I get a segmentation violation note and no output.

If it's a problem with MATLAB parsing windows.h, is there another header that I can use to fix this? I've read that there is another header stdbool.h (which is non-stanard) and perhaps I can find a code for it on the web.

Another solution that I'm considering is to write another .dll in C++ that converts the BOOL and the output to "MATLAB-friendly" types, and then use MATLAB to call that new .dll . Having no C++ experience at all, I can already feel the agony of doing so. Do you think that's going too far? Or in your experience is this a feasible solution?

Thanks again!

Qian

Philip Borghesani 2012-1-12

I agree with Walter the BOOL issue has been fixed. I expect that one of the values you are passing into the function is not correct. You will need to supply the MATLAB code you are using to call DLL_Get_Spectraband and more information like the pixel count you expect. I suggest creating a new question with this information.

Qian 2012-1-12

It has indeed been resolved! I'm not sure why it didn't work yesterday but it seems to run just fine now. Thanks guys!

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