Is there a possibility to set a QBitArray using a long int?

[Christian Ehrlicher]

Qt5 or Qt6?

https://doc.qt.io/qt-6/qbitarray.html#toUInt32

[Kevin470]

@Christian-Ehrlicher Qt6.
But I am looking for fromUInt32 and not toUInt32 unfortunately.

[Christian Ehrlicher]

Then use https://doc.qt.io/qt-6/qbitarray.html#fromBits

[Kevin470]

@Christian-Ehrlicher
Could you help me out with an example please?
I tried

    QBitArray bitArray;
    quint32 intvalue = 9999999;

    bitArray.fromBits(intvalue,32);
    qInfo() << "Size:" << bitArray.size();

and it throws an error saying main.cpp:12:23: Cannot initialize a parameter of type 'const char *' with an lvalue of type 'quint32' (aka 'unsigned int')

If I try the one below, the program crashes.

    QBitArray bitArray;
    quint32 intvalue = 9999999;

    bitArray.fromBits((char*)(intvalue),32);
    qInfo() << "Size:" << bitArray.size();

[jsulm]

@Kevin470 said in Is there a possibility to set a QBitArray using a long int?:

bitArray.fromBits((char*)(intvalue),32);

Shouldn't it be

bitArray.fromBits((char*)(&intvalue), 32);

?

[Kevin470]

@jsulm Oops sorry. Yes it should be bitArray.fromBits((char*)(&intvalue), 32);

But it still prints Size: 0

[jsulm]

@Kevin470 said in Is there a possibility to set a QBitArray using a long int?:

But it still prints Size: 0

Yes, because https://doc.qt.io/qt-6/qbitarray.html#fromBits is a static method...

[Kevin470]

@jsulm Thanks a lot. Works Perfectly!

QBitArray bitArray;
    quint32 intvalue = 9999999;

    bitArray = QBitArray::fromBits((char*)(&intvalue),32);
    qInfo() << "Size:" << bitArray.size();

[Christian Ehrlicher]

@Kevin470 Then please mark this topic as solved, thx.

[J.Hilk]

where's the downvote button!?!?! c-style casts 🫢

[Pl45m4]

@J-Hilk said in Is there a possibility to set a QBitArray using a long int?:

where's the downvote button

Casted to (void)downvoteBtn;

:)

[JonB]

@J-Hilk
I always have to go look it up, should this one be reinterpret_cast<>, or has C++ introduced yet another new one of these casting templates to use for this case?

Not to mention that the other day @Chris-Kawa wrote in https://forum.qt.io/topic/139176/qgraphicsitem-conversion-into-long-using-reinterpret_cast/2

I'll just mention that on some platforms pointers to different types can have different sizes too i.e. sizeof(char*) != sizeof(int*), so, although unlikely that it affects you, what you're doing is a risky business.

which seems to me to make a nonsense of half of these castings anyway...!

[J.Hilk]

@JonB

• static_cast for basic types
• dynamic_cast for pointers or references to polymorphic class types;
• const_cast const or volatile qualifiers;
• reinterpret_cast is for special circumstances and you think you know better than the compiler. Converting between pointers or references and completely unrelated types.

[Christian Ehrlicher]

@JonB said in Is there a possibility to set a QBitArray using a long int?:

which seems to me to make a nonsense of half of these castings anyway...!

They add validation if the cast is valid which is not available with the c-style cast.

[JonB]

@J-Hilk said in Is there a possibility to set a QBitArray using a long int?:

reinterpret_cast is for special circumstances and you think you know better than the compiler. Converting between pointers or references and completely unrelated types.

And that (reinterpret_cast<>) is what should be used in the case we are discussing (int * -> char *), right?

[Separate: did I see recently that C++20 or whatever has introduced yet another new somethingelse_cast<> construct beyond these 4, or do you think I'm imagining this?]

@Christian-Ehrlicher said in Is there a possibility to set a QBitArray using a long int?:

They add validation if the cast is valid which is not available with the c-style cast.

But not in the reinterpret_cast<> case which (I believe) we are going to use here, right?

[J.Hilk]

@JonB said in Is there a possibility to set a QBitArray using a long int?:

[Separate: did I see recently that C++20 or whatever has introduced yet another new somethingelse_cast<> construct beyond these 4, or do you think I'm imagining this?]

std::bit_cast

but, it's a library feature not a language feature.

Technically, if the OP uses c++20 it would be the "saver" option, otherwise reinterpret_cast