Calllib error: Array must be numeric or logical or a pointer to one

I need to use a function available in Fortran by a private library. Then, I created a DLL in Fortran with a function calling the private function and a header file in C++, so I can load my library to Matlab by loadlibrary. I was able to load it, but I get the following error when I try to call my function:

"Error using calllib

Array must be numeric or logical or a pointer to one."

I tried to change the format of the variables in my codes at Fortran and C++, but with no success. I receive the same error. My function receives another function as an input (it is a function_handle in Matlab), e.g.,

func = @(x) x^2 + x - 2

And, I specified it as a float in the header, which I don't know if it is the right way to do it.

My codes are the following:

DLL (Fortran 90, Visual Studio 2019, Intel Parallel XE Studio 2019):

DOUBLE PRECISION function rizzo_function(func, a, b, c, d, e)
!DEC$ ATTRIBUTES DLLEXPORT, ALIAS : "rizzo_function" :: rizzo_function
include 'library.h'
DOUBLE PRECISION a, b, c, d, e
EXTERNAL func, private_function

CALL private_function(func, a, b, c, d, e)

rizzo_function = c !c is one of the outputs (and inputs) of private_function.

END FUNCTION

Header File (C++):

#ifdef __cplusplus
extern "C" {
#endif
	__declspec(dllexport) double rizzo_function(float *func, double* a, double* b, double* c, double* d, double* e);
#ifdef __cplusplus
}
#endif

I set func as float because func(x), in private_function, is defined as:

real function func(x)
real, intent(in) :: x
end function

I am thinking the error is the wrong specification of func at C++ (or Fortran), but I don't know what should be its format.

Any help and suggestions would be gratefully received.

Thanks in advance,

Rafaela Rizzo.

Answer 1

[James Tursa]

This sounds very similar to the following post, where someone was trying to call a function that had a function pointer as one of its arguments (that "func" in your Fortran code is a function pointer). Read through the solution framework in this link and see if you can modify it for your needs. You will not be able to pass a MATLAB function handle into that Fortran function pointer spot, but maybe you can use an interface function like the one proposed in this post to call that function handle:

https://www.mathworks.com/matlabcentral/answers/480348-c-fortran-callback-to-matlab