swig c++ to python return unsigned char* by reference

Question

I'm using swig to wrap a c++ function to python like this:

int getBytes(unsigned char *& result, int length)

I have learnt from this question how to wrap a function returned char* by reference:

%typemap(in,numinputs=0) char*& (char* tmp) %{
    $1 = &tmp;
%}

%typemap(argout) char*& (PyObject* obj) %{
    obj = PyUnicode_FromString(*$1);
    $result = SWIG_Python_AppendOutput($result,obj);
%}

%typemap(freearg) char*& %{
    free(*$1);
%}

I tried to apply this to unsigned char* but failed and get the error that SWIG_Python_AppendOutput cannot convert an unsigned char** to signed char**. I searched python doc and didn't find a function which can convert an unsigned char** to unsigned char**. Anyone can help? Thanks!

Answer 1

It's long time ago that I have solved this question, the following is my solution:

%typemap(in, numinputs= 0) (unsigned char *&result, int &length) (unsigned char *temp, int len) %{
  $1 = &temp;
  $2 = &len;
%}

%typemap(argout) (unsigned char *&result, int &length)  %{
    PyObject* arg5 = 0;
    arg5 = SWIG_FromCharPtrAndSize((const char *)(*$1), *$2);

    PyObject* temp = NULL;
    temp = $result;
    $result = PyList_New(1);
    PyList_SetItem($result, 0, temp);
    PyList_Append($result, (PyObject*)arg5);//unsigned char *&
    PyList_Append($result, PyInt_FromLong(*$2));

    Py_DECREF(temp);
%}