Difference between revisions of "ToStdWStringAndBuiltInWchar"

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'''English''' [[toStdWStringAndBuiltInWchar-SimplifiedChinese|简体中文]]
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'''English''' [[toStdWStringAndBuiltInWchar SimplifiedChinese|简体中文]]<br />[[Category:HowTo]]<br />[[Category:snippets]]
  
=QString, std::wstring and built-in wchar_t=
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= QString, std::wstring and built-in wchar_t =
  
==Problem statement==
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== 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()] ''[qt.io]'' and [http://doc.qt.io/qt-5.0/qtcore/qstring.html#fromStdWString QString::fromStdWString()] ''[qt.io]''.
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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 &quot;QString::toStdWString()&quot;:http://doc.qt.io/qt-5.0/qtcore/qstring.html#toStdWString and &quot;QString::fromStdWString()&quot;:http://doc.qt.io/qt-5.0/qtcore/qstring.html#fromStdWString.
  
==Possible solution==
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== 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:
 
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:
  
Note that for other platforms the std::wstring may be implemented using uint32 (for ucs-4/utf-32) instead.
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<code>/*! Convert a QString to an std::wstring '''/<br />std::wstring qToStdWString(const QString &amp;str)<br />{<br />#ifdef _MSC_VER<br /> return std::wstring((const wchar_t''')str.utf16());<br />#else<br /> return str.toStdWString();<br />#endif<br />}
  
===Categories:===
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/*! Convert an std::wstring to a QString '''/<br />QString stdWToQString(const std::wstring &amp;str)<br />{<br />#ifdef _MSC_VER<br /> return QString::fromUtf16((const ushort''')str.c_str());<br />#else<br /> return QString::fromStdWString(str);<br />#endif<br />}</code>
 
 
* [[:Category:HowTo|HowTo]]
 
* [[:Category:snippets|snippets]]
 

Revision as of 10:05, 24 February 2015

English 简体中文

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
}