why to use QStringLiteral instead of QString

guru007

please look for follwing code

//your code here
 void setupUi(QMainWindow *Analyzer)
    {
        if (Analyzer->objectName().isEmpty())
            Analyzer->setObjectName(QStringLiteral("Analyzer"));

why we can't use Analyzer->setObjectName(QString("Analyzer"));
or
Analyzer->setObjectName("Analyzer");

JKSH

@guru007 said in why to use QStringLiteral instead of QString:

why we can't use Analyzer->setObjectName(QString("Analyzer"));
or
Analyzer->setObjectName("Analyzer");

See the QString documentation at http://doc.qt.io/qt-5/qstring.html#more-efficient-string-construction :

"Many strings are known at compile time. But the trivial constructor QString("Hello"), will copy the contents of the string, treating the contents as Latin-1. To avoid this one can use the QStringLiteral macro to directly create the required data at compile time. Constructing a QString out of the literal does then not cause any overhead at runtime."

VRonin

A detailed explanation is also available here: https://woboq.com/blog/qstringliteral.html (oddly enough it's the result #1 on my Google for the qstringliteral query)

guru007

Thanks for ur replies....
Is there any situation where we have to specifically used QStringliteral over to QString.

mrjj

@guru007
Hi
Its an optimization. You use QStringLiteral to avoid to constructing a QString and then copy data.
So it can make a difference in loops where lots of strings are used and other cases with
lots of access.
For a small program, it won't really matter but why not just use in all cases where it fits.
It won't hurt performance and there is no reason not to.

I cant think of a case where you HAVE to use QStringliteral.

VRonin

The only downside I found is that, being a macro, it breaks inline static code analysis in Visual Studio. Definitely a minor thing that should not stop you using it.

The only case where it'd avoid it is if there is an explicit overload for const char* or QLatin1String. for example:

QString base("base");
base.prepend("prepended"); //better
base.prepend(QStringLiteral("prepended")); //worse