ToStdWStringAndBuiltInWchar

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QString, std::wstring and built-in wchar_t

Problem statement

Qt advises to build your Qt based software without wchar_t as built-in type, just like the Qt libraries themselves. In some cases this is not desired by the environment or not possible because other libraries have been built with the built-in wchar_t type. This will cause obscure linker errors when using std::wstrings, and "QString::toStdWString()":http://doc.qt.io/qt-5.0/qtcore/qstring.html#toStdWString and "QString::fromStdWString()":http://doc.qt.io/qt-5.0/qtcore/qstring.html#fromStdWString.

Possible solution

Windows uses utf-16 for its character encoding, as does Qt. Using this information we can use the following code to work around the issue:

/*! Convert a QString to an std::wstring */
std::wstring qToStdWString(const QString &str)
{
#ifdef _MSC_VER
 return std::wstring((const wchar_t''')str.utf16());
#else
 return str.toStdWString();
#endif
}

/*! Convert an std::wstring to a QString */
QString stdWToQString(const std::wstring &str)
{
#ifdef _MSC_VER
 return QString::fromUtf16((const ushort''')str.c_str());
#else
 return QString::fromStdWString(str);
#endif
}