In one MEX file, I created an output matrix with the command (working fine):
plhs[0] = mxCreateNumericMatrix((mwSize)destLen, 1, mxUINT8_CLASS, mxREAL);
For speedup I wanted to use the dynamic memory uninitialized, which lead me to the undocumented command:
plhs[0] = mxCreateUninitNumericMatrix((mwSize)destLen, 1, mxUINT8_CLASS, mxREAL);
working also very fine within Win32 and Win64.
Using exactly the same code within my Linux environment leads to the following warning from compiler:
warning: assignment makes pointer from integer without a cast [enabled by default]
and the code crashes, which show, that the returned integer value is not that one pointing to the correct memory address.
What can I do to use mxCreateUninitNumericMatrix?
Undocumented MEX functions do not have a corresponding prototype in mex.h header file, so you'll have to explicitly write one yourself. In this case it will be:
EXTERN_C mxArray *mxCreateUninitNumericMatrix(mwSize m, mwSize n,
mxClassID classid, mxComplexity flag);
The EXTERN_C macro expands to extern "C" if you are using C++, otherwise to extern in C, that way you get correct linkage.
In C (not C++), any undeclared functions are assumed to be external functions that return an integer (at least that's the case with GCC compiler I think).