ToStdWStringAndBuiltInWchar: Difference between revisions

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'''English''' [[toStdWStringAndBuiltInWchar SimplifiedChinese|简体中文]]
[[Category:HowTo]]
[[Category:HowTo]]
[[Category:snippets]]
[[Category:Snippets::Misc]]


= QString, std::wstring and built-in wchar_t =
= QString, std::wstring and built-in wchar_t =
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== Problem statement ==
== 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 [http://doc.qt.io/qt-5.0/qtcore/qstring.html#toStdWString QString::toStdWString()] and [http://doc.qt.io/qt-5.0/qtcore/qstring.html#fromStdWString QString::fromStdWString()].
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 [http://doc.qt.io/qt-5/qstring.html#toStdWString QString::toStdWString()] and [http://doc.qt.io/qt-5/qstring.html#fromStdWString QString::fromStdWString()].


== Possible solution ==
== Possible solution ==
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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:
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:


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


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

Latest revision as of 12:27, 28 November 2016


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)
{
#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
}