[C++-sig] Re: const char arrays

[David Abrahams]

"Ralf W. Grosse-Kunstleve" <rwgk at yahoo.com> writes:

> --- Niall Douglas <s_sourceforge at nedprod.com> wrote:
>>   struct custom_string_to_python_str
>>   {
>>     static PyObject* convert(custom_string const& s)
>>     {
>>       return 
>> boost::python::incref(boost::python::object(s.value()).ptr());
>>     }
>>   };
>> 
>> Isn't this making use of boost.python's inbuilt std::string 
>> converter? ie; it's not converting to a python string itself.
>
> Yes. Just to keep the example simple. Or maybe because I was too lazy to figure
> out the raw C API call.

Err, no.  Trace it in a debugger; the conversion should not go through
std::string at all.  If it does I'm very surprised.

>> For some non-std::string based string, would it be more like:
>> 
>>   struct custom_string_to_python_str
>>   {
>>     static PyObject* convert(custom_string const& s)
>>     {
>>       return 
>> boost::python::incref(PyString_FromStringAndSize(s.text(), 
>> s.length()));
>>     }
>>   };
>
> Close, but I think you are leaking a reference count. This should do the job:
>
>   return PyString_FromStringAndSize(s.text(), s.length());
>
> The bottom line is that you have to return a new Python reference.
> How exactly you do this is entirely up to you.

On the other hand, Ralf's instincts were good; it's generally better
to use high-level Boost.Python calls than low-level Python 'C' API
calls.  When the converter mechanism is ready for us to document, it
will probably not be returning raw PyObject*s.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com