Mex function issues when executing in matlab

I have created a mex function using visual c++ 2010, and for some reason, the function works but once the function ends, it causes matlab to shut down. my function in c++ is called 'void main()'. I have found some documentation that suggests I rename to 'void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])' but when I try and use that (also fixed in my .def), i get the error 'error LNK2019: unresolved external symbol main referenced in function __tmainCRTStartup'. So i go into link properties under advanced and add in the following: '/ENTRY:mexFunction' but that is causing the error: 'error LNK2001: unresolved external symbol /ENTRY: mexFunction'. What do i do to make this function work correctly w/out shutting down my matlab!?!

Thank you in advanced for any help.

Answer 1

[Jan]

C++ MEX functions do neither require a .def file nor a main() function. The function mexFunction() is called instead, such that a minimal MEX file looks like:

#inlcude "mex.h"
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{  // Some dummy code:
  mexPrintf("Number of inputs:  %d\n", nrhs);
  mexPrintf("Number of outputs: %d\n", nlhs);
}

Save this as "dulltext.cpp" and compile it by mex dulltest.c. No main(), no .def.

This mexFunction can now convert the Matlab arrays of the type mxArray * to the corresponding C-arrays, call the calculation in C as subfunctions, and convert the results back to mxArray * as output to Matlab.

When Matlab shuts down after the execution of your code, the code contains a bug.

Answer 2

[Walter Roberson]

Remember that your entry point to a C++ program needs to be defined with

extern "C" {
 ....
}

Answer 3

[ryan]

Would i put that inside the .def file? Right now this is my .def:

LIBRARY LibName EXPORTS mexFunction

And my mexFunction is set up like so:

void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[] ) {

return; }

[Walter Roberson]

.def files are not part of the C++ language (but they might be part of a particular implementation.)

I do not know what goes into .def files.

[ryan]

and in my preprocesor calls I have this:

#define CBASED extern "C"
#define EXPORTED_FUNCTION __declspec(dllexport)

but i still get this error:

MSVCRTD.lib(crtexe.obj) : error LNK2019: unresolved external symbol main referenced in function __tmainCRTStartup

[ryan]

I am pretty sure it has something to do with the entry point, or something. But I thought the .def would take care of this...

[Walter Roberson]

For technical reasons, the real entry point for C programs (and presumably C++ as well) is not main() itself, but rather a routine that runs before main() does. If you were to manage to change your entry point to main then your C++ code would not function properly for buffered I/O or for dynamic memory allocation or for argv and argc.

I would suggest switching to int main instead of void main, and returning 0 from the routine.

[Jan]

@Walter: I disagree. Ryan wants to create a MEX-function. Then a main() is not required, neither as void nor as int.