Is a two dimensional array in a structure supported by loadlibarary interface in MATLAB?

How do I pass a two dimensional array inside a structure to MATLAB while using LOADLIBRARY interface.

Answer 1

[Murugavel Sivagnanam]

The ability to pass a two dimensional array in a structure is not available through LOADLIBRARY in MATLAB. Suppose following is the definition of the structure with p1 as the two dimensional array, p1.

typedef struct { 

    int p1[2][3]; 

    int p2; 

    int p3; 

} c_struct;

Following code shows the function foo which returns the pointer to a_struct created.

#include  

#include    

#include "mathworks_example.h" 

c_struct a_struct = {{{1,2,3},{4,5,6}},7,8}; 

EXPORTED_FUNCTION c_struct* foo() { 

return &a_struct;

}

If this structure is returned from the library to MATLAB. It would not be read correctly.

To workaround this issue, please generate a prototype file using the library and header. The protoype file for the above function definition would look like the following:

function [methodinfo,structs,enuminfo,ThunkLibName]=proto 

%PROTO Create structures to define interfaces found in 'mathworks_example1'. 

%This function was generated by loadlibrary.m parser version 1.1.8.25 on Mon Sep 20 17:13:34 2010 

%perl options:'mathworks_example1.i -outfile=proto.m -chunkfile=mathworks_example_thunk_maci64.c' 

ival={cell(1,0)}; 

% change 0 to the actual number of functions to preallocate the data. 

structs=[];

enuminfo=[];

fcnNum=1; 

fcns=struct('name',ival,'calltype',ival,'LHS',ival,'RHS',ival,'alias',ival,'thunkname', ival); 

MfilePath=fileparts(mfilename('fullpath')); 

ThunkLibName=fullfile(MfilePath,'mathworks_example_thunk_maci64'); 

% c_struct * foo (); 

fcns.thunkname{fcnNum}='voidPtrThunk';fcns.name{fcnNum}='foo'; 

fcns.calltype{fcnNum}='Thunk';

fcns.LHS{fcnNum}='c_structPtr'; 

fcns.RHS{fcnNum}=[];

fcnNum=fcnNum+1; 

structs.c_struct.members=struct('p1', 'int32#', 'p2', 'int32', 'p3', 'int32'); 

methodinfo=fcns;

The syntax of structure is interpreted by MATLAB by the following line in the above code:

structs.c_struct.members=struct('p1', 'int32#', 'p2', 'int32', 'p3', 'int32');

The parameter p1 is of the type 'int32' but the length of the array is missing. If p1 were a one dimensional array of length 5, the following would be the output in prototype file:

structs.c_struct.members=struct('p1', 'int32#5', 'p2', 'int32', 'p3', 'int32');

To workaround the limitation of two dimensional array in a structure please manually change the prototype file to assign the size of the two dimensional array, like the following:

structs.c_struct.members=struct('p1', 'int32#6', 'p2', 'int32', 'p3', 'int32'); 

% the number following the #, denotes the length of the array.

Now when we call the function using loadlibrary we would get a structure with p1 as a single dimensional array of length 6. We can reshape the array to a two dimensional array using the function RESHAPE.