Re: [Swig-user] Typemap of Python unicode to C++ std::string in UTF-8 encoding

[William S F. <ws...@fu...>]

On 19/10/13 11:21, Stefan Bellon wrote:
> Hi all,
>
> I'm interfacing C and Python 2.7 using SWIG 2.0.x. Previously I've only
> been using char* and const char* to create the mapping to the C side,
> but now I'd like to use C++ and directly interface std::string& as well.
>
> I have the convention that on the C/C++ side strings are internally
> represented in UTF-8 encoding. Therefore my Typemap for the pure C side
> currently looks like this:
>
> %typemap(in) const char * (PyObject *temp_obj = NULL),
>               char * (PyObject *temp_obj = NULL)
> {
>    // Python -> C
>    if (PyString_Check($input))
>    {
>      $1 = PyString_AsString($input);
>    }
>    else if (PyUnicode_Check($input))
>    {
>      temp_obj = PyUnicode_AsUTF8String($input);
>      if (temp_obj != NULL)
>      {
>        $1 = PyString_AsString(temp_obj);
>      }
>      else
>      {
>        SWIG_exception_fail(SWIG_RuntimeError,
>          "in method '$symname',
>          argument '$1_name' corrupt unicode");
>      }
>    }
>    else
>    {
>      SWIG_exception_fail(SWIG_TypeError,
>        "in method '$symname',
>        argument '$1_name' of type '$1_type'");
>    }
> }
>
> (Not sure, perhaps this can be even simplified, but it works.)
>
> However I am completely unsure of how to extend this to work with C++
> std::string as well.
>
> At present, I have
>
> %include "std_string.i"
> %include "std_wstring.i"
>
> in my .i file, and it works for Python "str", but not for "unicode":
>
> TypeError: in method 'test', argument 1 of type 'std::string'
>
> Any help of how to get Python 2.7 "unicode" to C++ std::string using
> UTF-8 encoding would be greatly appreciated!
You'll probably need to redefine all the std::string typemaps. This can 
be a bit mind boggling as the implementation is hidden behind a number 
of macros. I suggest using the preprocessor by running swig -E and 
looking for the std::string typemaps and then provide your own 
overrides. Probably you just need the 'in', 'out' typemaps for 
std::string and const std::string&, but it really depends on what you 
are using.

William