[C++-sig] Re: Automatic PyUnicode to 'const char*'

[Stefan Seefeld]

David Abrahams wrote:
> "Lijun Qin" <qinlj at solidshare.com> writes:
> 
> 
>>Hi all,
>>
>>I'm using boost.python to wrap the WTL (Windows Template Libaray), using VC
>>7.1 and porting some old code previously use win32ui.pyd.
>>Basically it is easy to do, though gccxml failed to parse the ATL/WTL code
>>so I can not use Pyste.
>>But there is a trouble, does anybody know how to automaticly convert
>>PyUnicode to 'const char *'? Without this, I have to change lot of code
>>lines to explictly use str() function.
> 
> 
> I'm not an expert in it, but I thought Unicode used 16- or 32- byte
> wchar_t characters.  How would you convert it to char const*?

unicode allows different encodings, some (such as utf-8) with variably
sized character representations. This means that conversions usually
can't be done on-the-fly without helper constructs, i.e. some memory
management is needed.

As an example, I'm doing such conversions in a xml library. The C
implementation uses 'xmlChar *', which is just an alias for 'char *',
but really holds utf-8 encoded text.
I convert it to various string types (the public API is parametrized
for the string type):

Here is the conversion between xmlChar * and std::string:

struct string_convert
{
   static std::string in(const xmlChar *buffer)
   {
     return buffer ? std::string((char *)buffer) : std::string();
   }
   static xmlChar *out(const std::string &buffer)
   {
     return (xmlChar *)buffer.c_str();
   }
};

And here is the conversion between xmlChar * and Qt's QString:

struct QStringConvert
{
   struct Converter
   {
      Converter(const QCString &s) : utf8(s) {}
      operator const xmlChar *() const
      { return (const xmlChar *)static_cast<const char *>(utf8);}
      QCString utf8;
   };

   static QString in(const xmlChar *buffer)
   {
     return buffer ? QString::fromUtf8((const char *)buffer) : QString();
   }
   static Converter out(const QString &buffer)
   {
     return Converter(buffer.utf8());
   }
};



Regards,
		Stefan