[Interest] problem converting QVariant UserType to Int

[Mandeep Sandhu]

>
> Output:
> =====
> UserTypeClass ctor 0x7fff6aa02710 3 -> 3
> UserTypeClass copy 0x7fff6aa02710 to 0x194eb20 3 (UserType copied into
> QVariant)
> UserTypeClass::toInt 0x7fff6aa026f0 false 26537440 (1st conversion
> failed, where did 26537440 come from?)

Seems like uninitialized value from a THIRD UserTypeClass @
0x7fff6aa026f0. I'm curious as to where this 3rd object came from?!

> UserTypeClass::toInt 0x194eb20 true 3 (second attempt seems correct, I
> expect 3.)
> main(): value = 3
> =====
>
> The call to value.toInt(&b) in main generates a call to
> QVariant::qNumVariantToHelper, which can do 2 attempts to make the
> conversion, both of which call back to UserTypeClass::toInt():
>
> from QVariant.cpp:
>
> template <typename T>
> inline T qNumVariantToHelper(const QVariant::Private &d,
> const HandlersManager &handlerManager, bool *ok, const T& val)
> {
> ...some code omitted...
>
> T ret = 0;
> if ((d.type >= QMetaType::User || t >= QMetaType::User)
> && QMetaType::convert(&val, d.type, &ret, t)) {
> return ret;
> }
>
> if (!handlerManager[d.type]->convert(&d, t, &ret, ok) && ok)
> *ok = false;
> return ret;
> }
>
>
> The first conversion attempt fails because UserTypeClass::toInt() finds
> m_Data > 3. I had to contrive that restriction to demonstrate the
> problem. Since I am able to return false, the second conversion is tried
> next and it turns out to be the correct one. Note that 'this' from the
> copy of UserTypeClass (line 2 of output) is the same as 'this' from the
> second attempt at conversion (line 4 of output).
>
> Am I doing this correctly? What is the difference between the two
> conversion attempts in QVariant::qNumVariantToHelper?
>
>
> Thanks,
>
> glenn
> _______________________________________________
> Interest mailing list
> Interest at qt-project.org
> http://lists.qt-project.org/mailman/listinfo/interest