Convert std::string to QString

Question

I've got an std::string content that I know contains UTF-8 data. I want to convert it to a QString. How do I do that, avoiding the from-ASCII conversion in Qt?

Solution 1

There's a QString function called fromUtf8 that takes a const char*:

QString str = QString::fromUtf8(content.c_str());

Solution 2

QString::fromStdString(content) is better since it is more robust. Also note, that if std::string is encoded in UTF-8, then it should give exactly the same result as QString::fromUtf8(content.data(), int(content.size())).

Solution 3

Since Qt5 fromStdString internally uses fromUtf8, so you can use both:

inline QString QString::fromStdString(const std::string& s) 
{
return fromUtf8(s.data(), int(s.size()));
}

Solution 4

Usually, the best way of doing the conversion is using the method fromUtf8, but the problem is when you have strings locale-dependent.

In these cases, it's preferable to use fromLocal8Bit. Example:

std::string str = "ëxample";
QString qs = QString::fromLocal8Bit(str.c_str());

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Comments

[Marc Mutz - mmutz]

More efficient: QString::fromUtf8( content.data(), content.size() )

[Rémi Benoit]

Only in Qt5. In Qt4 it uses QString::fromAscii.

[plasmacel]

In the C++ standard there is no guarantee, that std::string is encoded in UTF8 (actually the encoding is unspecified), so this answer is not entirely correct. At least you should check the encoding by an assertion.

[plasmacel]

This should be the accepted answer. However your last statement is not necessarily true. In the C++ standard there is no guarantee, that std::string is encoded in UTF8 (actually the encoding is unspecified), so QString::fromUtf8(content.data(), int(content.size())) may give different (and also incorrect) results than QString::fromStdString(content).