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

booleanccalllibdlldriverexternal interfacelib.pointerlibrarypointer

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!

Best Answer

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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MATLAB: Properly passing pointer arguments to .dll functions using loadlibrary and calllib

Your library is not correctly loaded, trying to call the functions in without fixing the load will only lead to frustration with pointers. I expect there were a large number of warnings from your call to loadlibrary. Ryan is on the correct track you need to have a header file that is compilable without prior includes for loadlibrary to work correctly. For these functions you need a definition of INT.

There are quite a few ways to solve the problem two options are: You can use the "mfilename" name option to loadlibrary and then fix the function definitions in the genereated header file. Or you can modify the header file or create a new one that has the correct #include statements in it.

I suggest fixing or creating a fixed header file. Look and a c example program for the library you are using and add any #include statements from it to the beginning of the header you are using with loadlibrary.

If you wish to create a new header file add the needed includes then a #include for the header you are trying to load. When you call loadlibrary use the addheader option and specify the original header name.

MATLAB: Does LIBFUNCTIONS not display more than 8 return arguments in MATLAB 7.6 (R2008a)

This is a limitation of the METHODS, METHODSVIEW, LIBFUNCTIONS, and LIBFUNCTIONVIEW functions in MATLAB release version up to and including MATLAB 7.6 (R2008a). METHODS -full does not list more then 8 output arguments and displays only the first output. Note that the function can still be called correctly and all outputs are returned.

A workaround to view the full function signature is to use the following:

libpkg=findpackage('lib'); 
class=findclass(libpkg,'fifteenArgDLL'); 
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The "method" variable would then contain information about the library:

%Sample invocation:
>> get(methods(1))
                  Name: 'myfun'
           Description: 'myfun'
             Signature: [1x1 schema.signature]
                Static: 'on'
      FirstArgDispatch: 'on'
>> get(methods(1).Signature)
       InputTypes: {16x1 cell}
      OutputTypes: {17x1 cell}
        Varargout: 'off'
         Varargin: 'off'
>> methods(1).Signature.OutputTypes
ans = 
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      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'
      'doublePtr'

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