What am I missing in my code ?

Decaration

QList<const QBluetoothDeviceInfo* > RemoteDeviceInfo;

This works

RemoteDeviceInfo.append(&info);

        // verify
        text = "!!!!!!!!!   DEBUG verify RemoteDeviceInfo \n";
        text += " name \n";
        text += RemoteDeviceInfo.at(0)->name();
        qDebug() << text;
        m_ui->plainTextEdit_8->appendPlainText(text);
        // m_ui->plainTextEdit_3->appendPlainText(text

      for(auto &device:RemoteDeviceInfo)
        {
            text = " BUILD  range loop test ";
            m_ui->plainTextEdit_8->appendPlainText(text);

            text = " device name ";
            text += device->name();
            m_ui->plainTextEdit_8->appendPlainText(text);
        }

when I attempt to verify RemoteDeviceInfo) using another method

it fails

if(!RemoteDeviceInfo.isEmpty()) passes OK
{
for (auto &device:RemoteDeviceInfo)
{
text = " For loop test ";
qDebug() << text;
text = " device address \n";
text += device->address().toString(); fails here
qDebug() << text;
m_ui->plainTextEdit_8->appendPlainText(text);
text = " device name \n";
text += device->name(); // >address().toString()
qDebug() << text;
m_ui->plainTextEdit_8->appendPlainText(text);

                        }
                    }
                }

My debug shows no contents in RemoteDeviceInfo when used in another method.

Example:

QList<QBluetoothDeviceInfo> RemoteDevicesList; //list of values

RemoteDevicesList.append(info); //append a value (copy it into the back of the list)
RemoteDevicesList.insert(17, info); //insert a copy of info at position 17
RemoteDevicesList.removeFirst(); //remove first element
RemoteDevicesList.removeLast(); //remove last element
RemoteDevicesList.removeOne(info); //remove first element which value equals info
QBluetoothDeviceInfo i1 = RemoteDevicesList.first(); //copy first element out to i1 variable
QBluetoothDeviceInfo i2 = RemoteDevicesList.last(); //copy first element out to i2 variable
QBluetoothDeviceInfo i3 = RemoteDevicesList.at(42); //copy 42nd element out to i3 variable

The above is when you have a list of values. If you have a list of pointers it's pretty much the same, but you deal with addresses, so & when you want to take an address of an object and * when you want to get an object a pointer points to:

QList<QBluetoothDeviceInfo*> RemoteDevicesList; //list of pointers

RemoteDevicesList.append(&info); //append an address of info object (pointer) to the back of the list
RemoteDevicesList.insert(17, &info); //insert a pointer to the info object at position 17
QBluetoothDeviceInfo i1 = *RemoteDevicesList.first(); //take the first pointer from the list, dereference it with * and copy it to i1 variable
QBluetoothDeviceInfo* i2 = RemoteDevicesList.first(); //take the first pointer from the list and copy it to i2 variable

Keep in mind that when you're dealing with pointers you have to make sure the objects they point to are still alive, otherwise the pointers will point to garbage and cause a crash when you try to access the objects through them.

why I am getting the error

Your list holds pointers and you're trying to pass an object reference to append().

OFFER A SOLUTION

Change the list type to match what you're passing or change what you're passing to match the list type.