Q_ENUM(enum_name) works with only enums declared inside class. srsly?

Kofr

Let's look at example from documentation which is copied next.

class Message : public QObject
 {
     Q_OBJECT
     Q_ENUMS(Status)
     Q_PROPERTY(Status status READ status NOTIFY statusChanged)
 public:
     enum Status {
         Ready,
         Loading,
         Error
     };
     Status status() const;
 signals:
     void statusChanged();
 };

In this example we declare our enumeration declared inside class with Q_ENUM(). It is ok. But what if we want to use Globally declared enumeration. Qt gives errors. How can we achieve operating with enumerations declared outside the class?

SGaist

Hi,

You can't, Q_ENUMS need a meta object provided either by the QObject class or the Q_GADGET macro

dethtoll

This is an old topic, but still comes up as one of the first Google results. I just wanted to add:

If the main goal is to use the enum as a property, it is sufficient to just use Q_DECLARE_METATYPE after the globally-declared enumeration.

If you need the other conveniences of Q_ENUM, then SGaist's reply applies.

raven-worx

@Kofr said in Q_ENUM(enum_name) works with only enums declared inside class. srsly?:

How can we achieve operating with enumerations declared outside the class?

This is possible since Qt 5.8 where the Q_NAMESPACE macro was introduced. This enables the generation of a MOC object also for namespaces.

namespace MyNamespace
{
    Q_NAMESPACE
 
    enum MyEnum {
        Foo,
        Bar
    };
    Q_ENUM_NS(MyEnum)
}

Note the Q_ENUM_NS macro here. There is also a Q_FLAG_NS macro available.

Drake Campbell

Let me know if this question does not belong on this post. I am on Windows 10 and my project configuration is set to use Qt 5.11.0 MSVC2015 64 bit. I created a new Qt Quick application and copy pasted the namespace deceleration as posted by raven-worx and compiled. I get the following errors which disappear if I remove the Q_NAMESPACE and Q_ENUM_NS statements.

qtprojects\QEnum\myenum.h:7: error: C2143: syntax error: missing ';' before 'enum [tag]'
qtprojects\QEnum\myenum.h:8: error: C4430: missing type specifier - int assumed. Note: C++ does not support default-int
qtprojects\QEnum\myenum.h:13: error: C2143: syntax error: missing ';' before '}'
qtprojects\QEnum\myenum.h:13: error: C4430: missing type specifier - int assumed. Note: C++ does not support default-int
QTProjects\build-QEnum-Desktop_Qt_5_11_0_MSVC2015_64bit-Debug\debug\moc_myenum.cpp:65: error: C2039: 'staticMetaObject': is not a member of 'Enums'
qtprojects\QEnum\myenum.h:4: see declaration of 'Enums'

I am also new so I feel like I may be missing something simple. The only things that exist are the default main.cpp and main.qml and a header file with the above pasted code. Thanks in advance.

Judit

You need to include QObject to make it work

Pixelgrease

To add to SGaist' response, below is an example of Q_ENUM in a struct with Q_GADGET:

struct Message 
{
     Q_GADGET
public:
     enum Status {
         Ready,
         Loading,
         Error
     };
     Q_ENUM(Status)
};

This precludes using signals and slots within the struct, is a lightweight solution for properties or unit test arguments. This works as far back as Qt 5.5.