How to convert enum to QString?

Question

I am trying to use the Qt reflection for converting enum to QString.

Here is the part of code:

class ModelApple
{
    Q_GADGET
    Q_ENUMS(AppleType)
public:
    enum AppleType {
      Big,
      Small
    }
}

And here is i trying to do:

convertEnumToQString(ModelApple::Big)

Return "Big"

Is this possible? If you have any idea about convertEnumToQString, please share it

score 79 · Accepted Answer · edited Nov 10 '17 at 09:13

79

You need to use Q_ENUM macro, which registers an enum type with the meta-object system.

enum AppleType {
  Big,
  Small
};
Q_ENUM(AppleType)

And now you can use the QMetaEnum class to access meta-data about an enumerator.

QMetaEnum metaEnum = QMetaEnum::fromType<ModelApple::AppleType>();
qDebug() << metaEnum.valueToKey(ModelApple::Big);

Here is a generic template for such utility:

template<typename QEnum>
std::string QtEnumToString (const QEnum value)
{
  return std::string(QMetaEnum::fromType<QEnum>().valueToKey(value));
}

edited Nov 10 '17 at 09:13

iammilind

68,093
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answered Dec 15 '15 at 05:53

Meefte

6,469
1
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8

`QMetaEnum::fromType` is available from Qt 5, it doesn't exist in Qt 4. You should add this remark. By the way, I don't recommend to use `QMetaEnum::key` since it take `index` as parameter, how come is he declared `enum AppleType { Big = 2, Small}` – Danh Dec 15 '15 at 05:58
4

From the docs, it looks like this is actually only available from Qt 5.5 thus I still need to use my method in the answer I gave (was about to update my code but have to use Qt 5.4 for now). – CJCombrink Dec 15 '15 at 06:27
'keyToValue()' can do the other way around: get the enum value from the string! – jaques-sam Dec 11 '18 at 12:58
I got this: undefined reference to MyClass::staticMetaObject . I copied the example from official page of Q_ENUM . – SuB Dec 02 '20 at 08:01

score 40 · Answer 2 · edited Dec 03 '18 at 11:22

Much more elegant way found (Qt 5.9), just one single line, with the help of mighty QVariant.

turns enum into string:

QString theBig = QVariant::fromValue(ModelApple::Big).toString();

Perhaps you don't need QMetaEnum anymore.

Sample code here:

ModelApple (no need to claim Q_DECLARE_METATYE)

class ModelApple : public QObject
{
    Q_OBJECT
public:
    enum AppleType {
      Big,
      Small
    };
    Q_ENUM(AppleType)
    explicit ModelApple(QObject *parent = nullptr);
};

And I create a widget application, calling QVaraint function there :

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <modelapple.h>
#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QString s = QVariant::fromValue(ModelApple::Big).toString();
    qDebug() << s;

}

MainWindow::~MainWindow()
{
    delete ui;
}

You can see that i try to output the string on console , which really did:

And sorry for reverse casting , i tried successfully in some project , but some how this time i met compiling error. So i decide to remove it from my answer.

Thanks for answering, looks like the method needs to add `Q_DECLARE_METATYPE(ModelApple::AppleType)`, and even added make it compiled successful, the result is an empty string. Could you please post the example code for this? — JustWe, Nov 20 '17 at 00:51
For anyone struggling with this solution: you need Q_OBJECT and Q_ENUM. Also your enum has to be public. — Cheesi, Feb 20 '19 at 11:54
@Cheesi you don't need `Q_OBJECT`: `Q_GADGET` is sufficient for this (unless you are really making a `QObject`). — Ruslan, Aug 19 '19 at 12:21

CJCombrink · Answer 3 · 2015-12-15T06:32:10.237

9

The following should get you going:

QString convertEnumToQString(ModelApple::AppleType type) {
    const QMetaObject metaObject = ModelApple::staticMetaObject;
    int enumIndex = metaObject.indexOfEnumerator("AppleType");
    if(enumIndex == -1) {
        /* The enum does not contain the specified enum */
        return "";
    }
    QMetaEnum en = metaObject.enumerator(enumIndex);
    return QString(en.valueToKey(type));
}

edited Dec 15 '15 at 06:32

answered Dec 15 '15 at 05:49

CJCombrink

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38

Why don't you join the declaration of `enumString` and `enumString = en.valueToKey(type);` it will call only 1 constructor instead of 1 constructor and 1 `operator =`. Also, we can eliminate the check with `-1` since we can sure that that enum is existed. – Danh Dec 15 '15 at 05:54
So i have to specify the enumerator "AppleType" ? – JustWe Dec 15 '15 at 05:56
@Danh Yes you can do that. My actual code is a template function that takes in the enum name and the enum value to return the string. I modified it to answer the question. My usage is `string = convertEnumToQString("AppleType", ModelApple::Big);` so I need to check for a valid enum and assert if not valid for debugging. Also I assert before the return thus the reason for first assigning and then returning (purely for debugging). – CJCombrink Dec 15 '15 at 06:23
1

I get the the point for the template. Regarding the declaration, assign, and return, I still think that we shouldn't take an extra step, – Danh Dec 15 '15 at 06:28
@user3308570 Unfortunately yes unless you have Qt 5.5 (then you can use the other answer) that is why I suggest adding the check for in case you decide to change the name of the enum in future. – CJCombrink Dec 15 '15 at 06:41
Okay,unfortunately i am using Qt 5.3. Thanks guys. – JustWe Dec 15 '15 at 07:01

Alexandr Kirilov · Answer 4 · 2020-05-20T09:57:38.870

7

For the global Enum declaring use this in any header file:

namespace YourNamespace {

Q_NAMESPACE

enum YourEnum: int {

    EnumValue1,
    EnumValue2
};
Q_ENUM_NS(YourEnum)

}

and this where you want to get Enum description:

QMetaEnum metaEnum = QMetaEnum::fromType<YourEnum>();
qDebug() << "Enum description: " << metaEnum.name() << "::" << metaEnum.valueToKey(YourEnum::EnumValue2);

edited May 20 '20 at 09:57

answered May 20 '20 at 09:41

Alexandr Kirilov

210
2
7

1

I had tried to get this to work numerous times over the years, and recently I tried your solution, and was successful! The trick was wrapping my "global" enum (ie: not contained within a class) inside a namespace. Thanks! – Doug Dec 07 '20 at 19:18
1

Such a helpful answer. Thank you!! – developer01 Oct 07 '21 at 21:11

score 2 · Answer 5 · edited May 23 '17 at 12:34

2

How about:

QString convertEnumToQString(ModelApple::AppleType type)
{
    const QMetaObject &mo = ModelApple::staticMetaObject;
    int index = mo.indexOfEnumerator("AppleType");
    QMetaEnum metaEnum = mo.enumerator(index);
    return metaEnum.valueToKey(type);
}

UPDATED: For Qt 5.5, see this answer

edited May 23 '17 at 12:34

Community

1
1

answered Dec 15 '15 at 05:50

Danh

5,916
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score 2 · Answer 6 · answered Jun 20 '17 at 13:09

I faced the same problem and this is how i solved it. This is especially for Qt 4.8

QString string = enumToString(ModelApple::Big);

QString ModelApple::enumToString(AppleType apple)
{
    int index = metaObject()->indexOfEnumerator("AppleType");
    QMetaEnum metaEnum = metaObject()->enumerator(index);
    return metaEnum.valueToKey(apple);
}

How to convert enum to QString?

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