MATLAB: How to get a C++ structure ‘behind’ a libpointer

c++ structureexternal function callMATLAB

Hi there
I'm using an old 7.5.0/R2007b version of Matlab, and I'm experiencing a problem when reading structures created by an external C++ function.
I'm calling the function
struct_new* GetStruct_new(uint16 const val);
via loadlibrary and calllib. I'm also using a prototype file to circumvent a packing problem I had some months ago.
The structure is declared as follows in C++ code:
typedef struct
{
  float32  u16_Upper;
  float32  u16_Lower;
  float32* pf32_Parameters;
}
match_s;
typedef struct
{
  uint16    u16_Start;
  uint16    u16_End;
  match_s*  ps_1st_Match;
  match_s*  ps_2nd_Match;
}
results_s;
typedef struct
{
  uint16   u16_Depth;
  uint16   u16_Width;
  uint16   u16_Height;
  uint16*  pu16_InData;
  uint16*  pu16_OutData;
  results_s s_Results[256];
  uint8  bla[256];
  uint8*  blubb[256];
}
struct_new;
…and in the prototype file:
structs.match_s.packing=4;
structs.match_s.members=struct('u16_ED_Upper', 'single', 'u16_ED_Lower', 'single', 'pf32_ED_Parameters', 'singlePtr');
structs.results_s.packing=4;
structs.results_s.members=struct('u16_Start', 'uint16', 'u16_End', 'uint16', 'ps_1st_Match', 'match_sPtr', 'ps_2nd_Match', 'match_sPtr');
structs.struct_new.packing=4;
structs.struct_new.members=struct('u16_Depth', 'uint16', 'u16_Width', 'uint16', 'u16_Height', 'uint16', 'pu16_InData', 'uint16Ptr', 'pu16_OutData', 'uint16Ptr', 's_Results', 'results_s#256', 'bla', 'uint8#256', 'blubb', 'uint8Ptr#256');
In Matlab I do the following:
>> addpath ('\\projects\Binford\KX-2500\')
>> loadlibrary ('KX_drives.dll', @KX-2500, 'alias', 'KX');
>> params = calllib('KX', 'GetStruct_new', 11);
>> par = get(params, 'Value');
>> par.s_Results
ans =
libpointer
This libpointer is my problem, as I have no clue how to resolve it into an array of s_Result structures and read/write them. I've searched the documentation, but I wasn't able to find something that could help me on this one; most exapmles were about creating pointers, not the opposite way.
Thanks in advance!

Best Answer

Given:
structs.struct_new.members=struct('u16_Depth', 'uint16', 'u16_Width', 'uint16', 'u16_Height', 'uint16', 'pu16_InData', 'uint16Ptr', 'pu16_OutData', 'uint16Ptr', 's_Results', 'results_s#256', 'bla', 'uint8#256', 'blubb', 'uint8Ptr#256');
I expect you are getting some warnings when you call loadlibrary. Loadlibrary cannot properly process 'results_s#256' or 'uint8Ptr#256 your options are to redeclare these fields as a vector of a basic data type or change your structure.
For structures this complex you may be better off with a mex file or writing a helper dll that can access the structure and return its members or pointers to the desired members.
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