How to convert a pointer value to QString?

Why not simply use QString & QString::sprintf ( const char * cformat, ... )

QString t;
// QString::sprintf adds 0x prefix
t.sprintf("%08p", ptr);

Using QString::arg():

MyClass *ptr = new MyClass();
QString ptrStr = QString("0x%1").arg((quintptr)ptr, 
                    QT_POINTER_SIZE * 2, 16, QChar('0'));

It will use the correct type and size for pointers (quintptr and QT_POINTER_SIZE) and will always prefix "0x".

Notes:
To prefix the value with zeros, the fourth parameter needs to be QChar('0').
To output the correct number of digits, QT_POINTER_SIZE needs to be doubled (because each byte needs 2 hex digits).

QTextStream appears to offer the functionality you seek, and operates simply on a void*.

const void * address = static_cast<const void*>(ptr);
QString addressString;
QTextStream addressStream (&addressString);
addressStream << address;
qDebug() << addressString;

Unlike the other approaches, it does not reference notions like the particular number "8" or casting to "qlonglong". Seems less worrisome, and is much like the prescribed method for std::string (though without getting std::string conversions involved)