Math Forum Discussions

Oliver Woodford

Posts: 598
Registered: 8/3/07

Re: Making C++ objects persistent between mex calls, and robust.
Posted: Jan 24, 2011 5:08 AM

Plain Text

"newuser asdf" wrote:
> Iit works now (without Integer->Double->Integer conversions).
> I know that the way I do all this (creating C++ memory leaks, that have to be cleaned up using Matlab...) is not very "clean" programming. But at least it works...

Good. It's worth noting that you are not creating C++ memory leaks; you are simply ensuring that MATLAB doesn't cause memory leaks if you accidentally clear a C++ object without first freeing the memory, by automatically freeing the memory when the object is cleared. There is nothing "unclean" about this; quite the opposite.

I posted the code for the MATLAB class side of things earlier. I'm now posting my code for the C++ side of things below. It includes error checking to make sure you don't convert any uint64 to a pointer, only the true C++ class pointers.

Hope it's useful.
Oliver

// Define types
#ifdef _MSC_VER
typedef __int32 int32_t;
typedef unsigned __int32 uint32_t;
typedef unsigned __int64 uint64_t;
#else
#include <stdint.h>
#endif

#define CLASS_HANDLE_SIGNATURE 0xa5a50f0f
template<class base> class class_handle: public base
{
public:
class_handle() : base() { signature = CLASS_HANDLE_SIGNATURE; }
~class_handle() { signature = 0; }
bool isValid() { return (signature == CLASS_HANDLE_SIGNATURE); }

private:
uint32_t signature;
};

template<class base> inline mxArray *convertPtr2Mat(class_handle<base> *ptr)
{
mxArray *out = mxCreateNumericMatrix(1, 1, mxUINT64_CLASS, mxREAL);
*((uint64_t *)mxGetData(out)) = reinterpret_cast<uint64_t>(ptr);
return out;
}

template<class base> inline class_handle<base> *convertMat2Ptr(const mxArray *in)
{
if (mxGetNumberOfElements(in) != 1 || mxGetClassID(in) != mxUINT64_CLASS || mxIsComplex(in))
mexErrMsgTxt("Input must be a real uint64 scalar.");
class_handle<base> *ptr = reinterpret_cast<class_handle<base> *>(*((uint64_t *)mxGetData(in)));
if (!ptr->isValid())
mexErrMsgTxt("Handle not valid.");
return ptr;
}

// Code for init_mex() - ISM3D is my C++ object class, but you use your own
class_handle<ISM3D> *ism = new class_handle<ISM3D>;

// Code for clear_mex()
class_handle<ISM3D> *ism = convertMat2Ptr<ISM3D>(prhs[0]);
delete ism;

// Code for action_mex
class_handle<ISM3D> *ism = convertMat2Ptr<ISM3D>(prhs[0]);
ism->action();