[solved] Doubts using QStringLiteral and QStringBuilder

luisborlido

Hi!

I've been reading the Qt documentation on "QString":http://qt-project.org/doc/qt-5/qstring.html to see how to correctly use it and I am a little bit confused.
In the documentation there is a macro called "QStringLiteral":http://qt-project.org/doc/qt-5/qstring.html#QStringLiteral, For what I understood, we should use it, depending of the cases, to prevent memory allocation, copy and conversion of const char*. Also that we should only use it when does not exist an overload to use "QLatin1String":http://qt-project.org/doc/qt-5/QLatin1String.html. But in the example for this case it is used QString::operator==, but the available overloads are:
@bool operator==(const QByteArray & other) const
bool operator==(const char * other) const@

So instead of
@if (attribute.name() == QLatin1String("http-contents-length")) //...@

should not be written
@if (attribute.name() == "http-contents-length") //... ?@

Also, what of the following best describes an optimized initialization of a QString?
@QString first = "ångström";
QString second = QLatin1String("ångström");
QString third = QStringLiteral("ångström");@

There is also another topic where I have some doubts: "More Efficient String Construction":http://qt-project.org/doc/qt-5/qstring.html#more-efficient-string-construction.
In this topic one refers that can be used QStringBuilder and gives the following example:
@QString foo;
QString type = "long";

foo->setText(QLatin1String("vector<") + type + QLatin1String(">::iterator"));

if (foo.startsWith("(" + type + ") 0x"))
...@

But one does not shows the alternate version using the QStringBuilder. Is this the best (optimized) way to use it?
@
#include <QStringBuilder>
...
QString foo;
QString type = "long";

foo->setText("vector<" % type % ">::iterator");

if (foo.startsWith("(" % type % ") 0x"))
...@

And finally, is this correct?
@QString testString = tempString % " minutes";
if (executeThisCondition)
testString = testString & " or seconds";@

Or should we use QString::operator+= and QString::append?

Thanks for your time and patiente ;-)

sierdzio

This post is much better suited for Interest mailing list, where the developers who wrote QString are present.

I'll give you some answers, but treat them with caution, as I am far from being an expert on this.

I think in your first example, the comparison with const char is fine

I think the best is a fourth option, where you don't create any temporary value: @ QString third("ångström"); @

QStringBuilder is used automatically by QString in Qt 5.x and Qt 4.8+. AFAIK, you do not need to use any special syntax for it to work

If you want other developers to understand your code, use operator+= or ::append()

luisborlido

Thanks for your reply. I'm sorry for the the delay; I've been busy with other projects and hadn't the time to check out the forum.

I think there is no need to send to mailing list since you have fulfilled all my doubts.

Do I need to change the subject to close this discussion?

sierdzio

[quote author="luisborlido" date="1413201000"]Thanks for your reply. I'm sorry for the the delay; I've been busy with other projects and hadn't the time to check out the forum.

I think there is no need to send to mailing list since you have fulfilled all my doubts.

Do I need to change the subject to close this discussion?[/quote]

OK, no problem.

I've marked the thread as solved for you. Have fun :-)