Problems with struct pointer pointer in calllib

I'm working with a header that has the following declaration:

struct ADI_FileHandle__ { int unused; }; typedef struct ADI_FileHandle__ *ADI_FileHandle;

One function I am using is:

DLLEXPORT ADIResultCode ADI_OpenFile(const unsigned short* path, ADI_FileHandle* fileH, ADIFileOpenMode mode);

My Matlab code calling this is:

result = calllib('ADIDatIOWin','ADI_OpenFile',int16(file_path),file_handle_pointer,file_open_mode);

This results in a value for unused (structure field in ADI_FileHandle__ ). A typical value is something like 1654585380. The result value indicates a success.

I then try to call another function:

DLLEXPORT ADIResultCode ADI_GetNumberOfChannels(ADI_FileHandle fileH, long* nChannels);

in Matlab as:

            file_handle_pointer = libpointer('ADI_FileHandle__Ptr');
            set(file_handle_pointer,'Value',struct('unused',int32(1654585380)))
            n_channels_pointer = libpointer('longPtr');
            result = calllib('ADIDatIOWin','ADI_GetNumberOfChannels',file_handle_pointer,n_channels_pointer);

At this point Matlab crashes.

What am I missing?

Thanks, Jim

[Jim Hokanson]

Note, I tried this link and had no luck.

http://www.mathworks.com/matlabcentral/answers/96578-why-does-matlab-crash-when-i-make-a-function-call-on-a-dll-in-matlab-7-6-r2008a

[Kaustubha Govind]

Sorry, I mistakenly created an answer (and deleted it), after realizing that you do follow the documentation: http://www.mathworks.com/help/matlab/matlab_external/working-with-pointers.html#f50712

[Friedrich]

Are you sure the DLL can handle a made up file_handle_pointer? I would assume it crashes because no actual valid file was opened and hence the DLL crashes.

Have you tried calling the ADI_GetNumberOfChannels function from a plain C application with the exact same inputs?

[Jim Hokanson]

@Friedrich,

I should clarify, the input to the second function is the numerical result of unused from the first. There is however an additional level of redirection that I'm not quite sure that I'm handling correctly. Something like:

A => points to => B => points to => C (which is a structure)

A : ADI_FileHandle*

B : ADI_FileHandle == typedef struct ADI_FileHandle__ *ADI_FileHandle

C : ADI_FileHandle__

I think what I am passing to the second function is C (ADI_FileHandle__), not ADI_FileHandle (Notice the missing trailing underscores)

I'm giving the mex a shot now ...

[Jim Hokanson]

Well, after many hours of making silly mistakes in mex, the code works just fine (in mex). I think the problem is the inability to get the double pointer on the structure working as intended.