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How can I create a pointer to a structure with more than 3 elements?

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Hello to eveyone. I am trying to write a MATLAB code able to use the DLL library of WaveVision5 from Texas Instruments, in order to control my ADC Development board. I am just trying now to call a function from the DLL, in order to see if the library is up and working.
Of course there is a little bit to have a look at what kind of data I will need, for example the function which I am trying to call is taking in input some kind of data defined inside the library header.
Now my function is taking in input: * A pointer to a ulong (which on my MATLAB should be a int32) * A pointer to a null terminated string * A pointer to a structure composed by four ulong.
typedef struct {
/** Major */
WvWord Major;
/** Minor */
WvWord Minor;
/** Release */
WvWord Release;
/** Build */
WvWord Build;
} WvVersionNumber;
Now the problem is that I have created the first two pointers without problems, but it seems like I am not able to create a pointer to a structure containing more than 3 elements, for instance:
sm = struct('p1', int32(0), 'p2', int32(0), 'p3', int32(0), 'p4', int32(0));
sp = libpointer('c_struct',sm);
I receive the followind error:
A field does not match one in the struct.
Error in libpointer (line 18)
ptr=lib.pointer(varargin{:});
Error in ADC_test (line 34)
sp = libpointer('c_struct',sm);
Instead if I just get rid of one of those fields inside the structure, everything looks fine.
I suppose that using c_struct is not the best way to do this, how can I create the wanted pointer? Any ideas?
Best Regards, Giovanni

  1 Comment

dpb
dpb on 25 Jul 2013
I've not used libpointer but it says in the doc that
P = libpointer('TYPE') returns an empty pointer to the given TYPE.
TYPE can be any MATLAB numeric type, or a structure or enum defined in a loaded library.
From that I infer that the problem is that your sm is a Matlab structure and not one from a loaded library. Looks to me like you need
doc loadlibrary
doc libstruct

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Accepted Answer

Philip Borghesani
Philip Borghesani on 29 Jul 2013
dpb is correct the code should be something like:
% call loadlibrary to load mylib
sm = struct('Major', 0, 'Minor', 0, 'Release', 0, 'Build', 0) %let MATLAB worry about data types
verStruct=libstruct('WvVersionNumber',sm);
calllib('mylib','myfun', 0 ,'the string',verStruc);

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