How to make String to const wchar_t* conversion function work under Windows and Linux

Question

I work on a project written for MSVCC / Windows, that I have to port to GCC / Linux. The Project has its own String Class, which stores its Data in a QString from Qt. For conversion to wchar_t* there was originally this method (for Windows):

const wchar_t* String::c_str() const
{
    if (length() > 0)
    {
        return (const wchar_t*)QString::unicode();
    }
    else
    {
        return &s_nullString;
    }
}

Because unicode() returns a QChar (which is 16 Bit long), this worked under Windows as wchar_t is 16 Bit there, but now with GCC wchar_t is 32 Bit long, so that doesn't work anymore. I've tried to solve that using this:

const wchar_t* String::c_str() const
{
    if ( isEmpty() )
    {
        return &s_nullString;
    }
    else
    {
        return toStdWString().c_str();
    }
}

The problem with this is, that the object doesn't live anymore when this function returns, so this doesn't work eiter. I think the only way to solve this issue is to either:

1. Don't use String::c_str() and call .toStdString().c_str() directly
2. Make GCC treat wchar_t as 16 bit type

Possibility one would mean several hours of needless work to me and I don't know if possiblity 2 is even possible. My question is, how do I solve this issue best? I'd appreciate any useful suggestion. Thank you.

Answer 1

In my opinion, there are 2 ways :

1. convert QString to wchar_t* when needed
2. Let QString to store wchar_t* and return QString::unicode directly

These two functions can convert a QString to std::string and std::wstring
QString::toStdWString
QString::toStdString

To build QString as ucs4 :

#define QT_QSTRING_UCS_4
#include "qstring.h"

This can be used in qt3(qstring.h). I can't find the source of qt4.