c++ - cannot convert parameter 2 from 'mxArray **' to 'mwArray &' -

i want create c++ shared library matlab using deloytool , use in mvs. compile function name 'foo.m', result got list of files (.h,.cpp,.lib,...) , found function in 'foocpplib.h' follow:

extern lib_foocpplib_cpp_api void mw_call_conv foo(int nargout, mwarray& y, const mwarray& x); 

then create mvs project (2010), window form application, 2 textbox , 2 click button, 1 textbox named inbox, , named outbox. code inside button_click follow:

private: system::void button1_click(system::object^  sender, system::eventargs^  e) { double input = system::double::parse(inbox->text); mxarray *x_ptr; mxarray *y_ptr=null; double *y;  // create mxarray input mlffoo x_ptr = mxcreatedoublescalar(input);  // call implementation function  // note second input argument should &y_ptr instead of y_ptr.  foo(1,&y_ptr,x_ptr);  // return value mlffoo mxarray.  // use mxgetpr pointer data contains. y = (double*)mxgetpr(y_ptr);  // display result in form outbox->text = ""+*y;  //clean memory mxdestroyarray(x_ptr); mxdestroyarray(y_ptr); } 

when build project, error occurred below:

error c2664: 'foo' : cannot convert parameter 2 'mxarray **' 'mwarray &' types pointed unrelated; conversion requires reinterpret_cast, c-style cast or function-style cast. 

note: included 'foocpplib.h' in .cpp source file.

could me this! thank you!

when parameter declared as

typename &argname 

it means argname reference. in c++ can pass parameters reference, allows function modify variable pass (among other things).

if have pointer, function expects reference, need dereference pointer in call asterisk, rather taking address of pointer ampersand:

foo(1,*y_ptr,*x_ptr); //    ^      ^ //    |      | //  here , here 

you can think of variables, pointers, pointers pointers, etc. in terms of level of indirection. variables have level of indirection of zero; pointers have level of indirection of one; pointers pointers have level of indirection of two, , on.

adding ampersand increases level of indirection; adding asterisk decreases it. variables, references have level of indirection of zero. if have pointer , need variable, must decrease level of indirection prepending asterisk.

another problem in code foo expects references mwarray, "w", passing references mxarray, "x". types need match, otherwise compiler not going take program.