Inserting QObject * in QMap - cannot initialize or pass the pointer

Question

I have two classes set up, InputFile and InputStream. Both inherit QObject, and are initialized with the Q_OBJECT macro.

InputFile contains a QMap<int,InputStream*>, creates InputStream objects and inserts them in the QMap.

InputStream is initialized with an explicit constructor, then inserted into the map like this:

InputStream myStream = InputStream(this, *myParameter);
_myMap.insert(myInt, *myStream);

The compiler returns a few errors in reference to my insertion call:

/opt/Qt5.5.0/5.5/gcc/include/QtCore/qobject.h:461: error: 'QObject::QObject(const QObject&)' is private
 Q_DISABLE_COPY(QObject)
                ^  

/home/myusername/Documents/Projects/MyProject/inputfile.cpp:17: error: no match for 'operator*' (operand type is 'InputStream')
             _myMap.insert(myInt, *myStream);
                                ^

I then tried to initialize InputStream as a pointer:

InputStream *myStream = InputStream(this, *myParameter);

In this case, the compiler returns the following error:

/home/myusername/Documents/Projects/MyProject/inputfile.cpp:16: error: cannot convert 'InputStream' to 'InputStream*' in initialization
             InputStream *myStream = InputStream(this, *myParameter);
                                                                        ^

I have also tried to use a reference (&) in the insert call, but this still returns the first error.

How can I initialize my object as needed and insert it in my QMap?

score 0 · Accepted Answer · answered Sep 24 '15 at 19:27

First error means that you can't copy QObject subclass, so you should use pointer to it (as you said in the beginning), so you need your second approach, but you forgot allocate memory and construct object( you forgot new keyword). So use just:

InputStream *stream = new InputStream(...);

score 0 · Answer 2 · answered Sep 24 '15 at 19:28

If _myMap is really a QMap<int,InputStream*> then you should insert just the raw pointer, not the object pointed at by the pointer:

_myMap.insert(myInt, myStream);

The error message is telling you that you cannot copy QObjects. Here is an explanation as to why QObjects are not copyable.

Inserting QObject * in QMap - cannot initialize or pass the pointer

2 Answers2