MATLAB crashes due to calllib (C++ .h file and FORTRAN .dll)

Question

I am trying to include an external FORTRAN-based (compiled with the Intel Fortran compiler) DLL in MATLAB. As it is external, I cannot make any adjustments to the runtime library of the DLL. Currently, I wrote an accompanying header file in C++ to be able to call the DLL. Using loadlibrary the library is loaded into MATLAB (no errors - one warning), however, when using calllib MATLAB crashes and does not provide an error.

I think one of the following might be the reason for this, but as I am an inexperienced in using DLL's (especially coding in C++) I did not yet find the error myself.

• There is also a .lib file that I got from the supplier, but I did not incorporate this yet in the MATLAB file or C++ header file.
• The FILEA and FILEB variables are paths to two text files that are input to the DLL, I think I might not have correctly incorporated these in C++.
• In the mHeader file (MATLAB header file) stdcall is only mentioned in the commented section and not in the coding section.

The code for the header file in C++ and my MATLAB script is shown below:

#ifndef _MYMODEL
#define _MYMODEL
#ifdef __cplusplus
extern "C" {
#endif // _cplusplus
    // Functions and data types defined
     void __stdcall MYFUN(char FILEA[], char FILEB[], int *IDTask, int 
    *nErrorCode, int *ErrorCode, double *Props, double *Out1, double *Out2, 
    double *Out3, double *Out4, double *Out5);
#ifdef __cplusplus
}
#endif // __cplusplus
#endif // !_MYMODEL      

MATLAB (r2018b):

%% Input to model
FILEA       = 'PATH\FILEA.txt';
FILEB       = 'PATH\FILEB.txt';
IDTask      = 1; %Multiple tasks possible in the .dll
%% Determine pointers
lpFILEA         = libpointer('cstring', FILEA);
lpFILEB         = libpointer('cstring', FILEB);
lpIDTask        = libpointer('int32Ptr', IDTask);
lpnErrorCode    = libpointer('int32Ptr');
lpErrorCode     = libpointer('int32Ptr');
lpProps         = libpointer('doublePtr');
lpOut1          = libpointer('doublePtr');
lpOut2          = libpointer('doublePtr');
lpOut3          = libpointer('doublePtr');     
lpOut4          = libpointer('doublePtr');
lpOut5          = libpointer('doublePtr');      

%% LoadLibrary
    [notfound, warnings] = loadlibrary('MYMODEL.dll','MYMODEL.h' ,'mfilename', 'mHeader');
%% Call .dll
[~,~, ~, nErrorOut, ErrorCodeOut, PropsOut, Out1_, ~, ~, Out4_, Out5_] ...
    = calllib('MYMODEL', 'MYFUN', lpFILEA, ...
    lpFILEB, lpIDTask, lpnErrorCode, lpErrorCode, lpProps, lpOut1, ...
    lpOut2, lpOut3, lpOut4, lpOut5);

Thanks in advance for your help!

Answer 1

I think your problem is that you are passing NULL pointers to your FORTRAN function, which will then attempt to write to an illegal address. You need to allocate memory for the outputs first, and pass the pointers to this memory to your function. Something like this:

% Input to model
FILEA       = 'PATH\FILEA.txt';
FILEB       = 'PATH\FILEB.txt';
IDTask      = 1;
% Determine pointers
lpnErrorCode    = libpointer('int32Ptr',0); % !!! You need to know the size of these outputs!
lpErrorCode     = libpointer('int32Ptr',0);
lpProps         = libpointer('doublePtr',zeros(10,1)); 
lpOut1          = libpointer('doublePtr',zeros(4,1));
lpOut2          = libpointer('doublePtr',zeros(8,1));
lpOut3          = libpointer('doublePtr',zeros(2,1));     
lpOut4          = libpointer('doublePtr',zeros(5,1));
lpOut5          = libpointer('doublePtr',zeros(7,1));      

% LoadLibrary
[notfound, warnings] = loadlibrary('MYMODEL.dll','MYMODEL.h' ,'mfilename', 'mHeader');
% Call DLL
calllib('MYMODEL', 'MYFUN', [uint8(FILEA),0], [uint8(FILEB),0], ...
        IDTask, lpnErrorCode, lpErrorCode, lpProps, lpOut1, ...
        lpOut2, lpOut3, lpOut4, lpOut5);
% Get output values
nErrorCode = lpnErrorCode.Value;
clear lpnErrorCode
ErrorCode = lpErrorCode.Value;
clear lpErrorCode
% ... etc.

For each of these outputs, I created data using the zeros function. The first two are scalar values (one data element), the others are arrays of various sizes. I have no idea what your FORTRAN function expects there, so I just made up some sizes. Please check your function to see what memory sizes each pointer should point to.

Note that I also changed how you pass the input data to your function. MATLAB should automatically convert the data to the right types. [uint8(FILEA),0] creates a zero-terminated c-style string from the MATLAB char array FILEA. In C strings must be terminated with a zero. I don't know how FORTRAN determines the length of a string, I presume it is the same, since the function uses a "C" interface.