Why we use "QT_USE_NAMESPACE" in some of Qt Programs?

[PooyaSis]

Hi
In many cases I've seen that people use "QT_USE_NAMESPACE".
I googled it, and couldn't find anything..
What's the purpose of "QT_USE_NAMESPACE" , and why do we use it?
Why there is nothing about it around!!!! :/

[aha_1980]

Hi @PooyaSis

You can compile Qt yourself within a namespace, e.g. to use a diffent Qt version within a plugin than the program that loads the plugin uses. More information here: https://wiki.qt.io/Qt_In_Namespace

I have not seen QT_USE_NAMESPACE so far, only QT_BEGIN_NAMESPACE and QT_END_NAMESPACE.

Where did you see QT_USE_NAMESPACE?

[PooyaSis]

@PooyaSis said in Why we use "QT_USE_NAMESPACE" in some of Qt Programs?:

QT_USE_NAMESPACE

Thanks a lot.
It was here in this example:

http://doc.qt.io/qt-5/qtserialport-cwriterasync-serialportwriter-cpp.html

[FloatFlower.Huang]

@PooyaSis
In Qt source code, you can check qtbase/src/corelib/global/qglobal.h
You will find that

#define QT_USE_NAMESPACE using namespace ::QT_NAMESPACE;

Here is the source code, you can find it at line 133
https://github.com/qt/qtbase/blob/5.10/src/corelib/global/qglobal.h