No appropriate default constructor available when defining a struct inside QMap

[lansing]

I have a list of one key multiple values to insert into a container.

id: "png", description: "this is png", quality: 100
id: "jpg", description: "this is jpg", quality: 0

id is the key and description and quality are the values. I tried to do this with QMap with a struct at the value position

    struct ImageProp {
        QString description;
        int quality;

        ImageProp(QString d, int qu)
            : description(d), quality(qu)
        {}
    };

    typedef QMap<QString, ImageProp> ImageFormat;
    ImageFormat imageFormatMap;

    imageFormatMap.insert("png", ImageProp("this is png", 100));

The editor detected no error, but when I ran it I got the errors:

'MyClass::ImageProp' no apprpriate default constructor available

C:\Qt\5.15.0\msvc2019_64\include\QtCore\qmap.h:679: error: C2664: 'void QMap<QString, MyClass::ImageProp>::insert(const QMap<QString, MyClass::ImageProp> &)': cannot convert argument 1 from 'const Key' to 'const QMap<QString,MyClass::ImageProp> &'
with
[
   Key=QString
]

For some reason it's not reading my constructor.

[SGaist]

Hi,

A default constructor is a constructor that requires no parameters to be used. So it either have no parameters or all parameters have a default value.

[lansing]

@SGaist

Thanks, adding a blank constructor for the struct solved it.

    struct ImageProp {
        QString description;
        int quality;

        ImageProp() {}

        ImageProp(QString d, int qu)
            : description(d), quality(qu)
        {}
    };

[Christian Ehrlicher]

@lansing This leaves quality uninitialzed...

This is much better, it also avoids one useless copy

struct ImageProp {
  QString description;
  int quality = 0;
  ImageProp() = default;
  ImageProp(const QString &d, int qu)
    : description(d), quality(qu)
  {}
};

[lansing]

@Christian-Ehrlicher

Thanks I'll do that. And why the use of QString &d instead of QString d in the argument?

[Christian Ehrlicher]

@lansing said in No appropriate default constructor available when defining a struct inside QMap:

And why the use of QString &d instead of QString d in the argument?

To avoid a copy of the QString object

[SGaist]

@lansing said in No appropriate default constructor available when defining a struct inside QMap:

@Christian-Ehrlicher

Thanks I'll do that. And why the use of QString &d instead of QString d in the argument?

The const is important in const QString &

[lansing]

@Christian-Ehrlicher @SGaist

Okay I got it. I'll use const QString & from now on.