Variable name strings used to be a part of the mxArray itself. However, that hasn't been the case for several years now. There is no easy way to recover the name of the passed variable other than to use mexCallMATLAB with "whos" and do an exhaustive search for the variable mxArray address to discover its name in the caller's workspace. So, you can either do that, or just drop that part of the test completely out of your mex code.
EDIT
If you really think you need this functionality, you could use the following function. The difference for this function compared to the original is that this function returns a pointer to dynamically allocated memory, so you might want to mxFree( ) it (or allow MATLAB to garbage collect it).
char *mxGetName(const mxArray *mx)
{
mxArray *lhs[1];
mxArray *cell;
size_t i, n;
char *varname;
varname = (char *) mxMalloc(65);
if( mx ) {
mexCallMATLAB(1,lhs,0,NULL,"who");
n = mxGetNumberOfElements(lhs[0]);
for( i=0; i<n; i++ ) {
cell = mxGetCell(lhs[0], i);
mxGetString(cell, varname, 65);
if( mx == mexGetVariablePtr("caller", varname) ) {
mxDestroyArray(lhs[0]);
return varname;
}
}
mxDestroyArray(lhs[0]);
}
varname[0] = '\0';
return varname;
}
