Difference between revisions of "ToStdWStringAndBuiltInWchar"

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'''English''' [[toStdWStringAndBuiltInWchar SimplifiedChinese|简体中文]]<br />[[Category:HowTo]]<br />[[Category:snippets]]
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[[Category:HowTo]]
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[[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 &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.
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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 [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 '''/<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 />}
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'''Convert a QString to an std::wstring'''
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<code>
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std::wstring qToStdWString(const QString &str)
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{
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#ifdef _MSC_VER
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return std::wstring((const wchar_t*)str.utf16());
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#else
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return str.toStdWString();
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#endif
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}
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</code>
  
/*! 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>
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'''Convert an std::wstring to a QString'''
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<code>
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QString stdWToQString(const std::wstring &str)
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{
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#ifdef _MSC_VER
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return QString::fromUtf16((const ushort*)str.c_str());
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#else
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return QString::fromStdWString(str);
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#endif
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}
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</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) {

  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

}