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() and QString::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) {

  1. ifdef _MSC_VER
return std::wstring((const wchar_t)str.utf16());
  1. else
return str.toStdWString();
  1. endif

}

/*! Convert an std::wstring to a QString */ QString stdWToQString(const std::wstring &str) {

  1. ifdef _MSC_VER
return QString::fromUtf16((const ushort)str.c_str());
  1. else
return QString::fromStdWString(str);
  1. endif

}