V1.2
Hello!
Recently I wrote
a post about a better way of performing type casting in C++ when needing the use of the problematic
reinterpret_cast. Now I woud like to write some comments about another "casting", namely between a struct and a QByteArray.
Conversion using QDataStream
A conversion
from a struct
to a QByteArray can be usefull when somebody, for example, handles some data inside a struct and want to send it through a interface that works with QByteArray such as
QIODevice. At the other side of the system, the received QByteArray may be needed
to be converted back to a defined struct for proper handling.
In accordance to some references, the proper way of doing this is by constructing serialization and de-serialization methods specifically for doing such a job using
QDataStream.
Here is a example for a serialization method:
QByteArray serialize()
{
QByteArray byteArray;
QDataStream stream(&byteArray, QIODevice::WriteOnly);
stream.setVersion(QDataStream::Qt_4_5);
stream << status_change_id
<< result_code
<< reserved[0]
<< reserved[1]
<< reserved[2];
return byteArray;
}
And here how to deserialize some data:
void deserialize(const QByteArray& byteArray)
{
QDataStream stream(byteArray);
stream.setVersion(QDataStream::Qt_4_5);
stream >> status_change_id
>> result_code
>> reserved[0]
>> reserved[1]
>> reserved[2];
}
Other options
Another option (now exclusivaly about converting from a QByteArray to a struct) is doing a cast of the QByteArray to a pointer of void and then static-casting to the desired struct, either in a const or non-const way:
void convertToStruct(const QByteArray& byteArray)
{
//constData() used because const is desired; otherwise, prefer data() don't forgetting deep copy issues
const void* poTemp = (const void*)byteArray.constData();
const MyStruct* poStruct = static_cast< const MyStruct* >(poTemp);
}
Conclusion
In this article we saw how to do proper casting between a struct and a QByteArray, something that may come in handy many times when working with more advanced applications. About the usage of QDataStream for doing this work, I'ld suggest a reading on
this forum thread where I had a discussion about the usage of QDataStream for such context. Another interesting reading would be
this other thread where I discussed about other methods of doing this work and some other, more generalized suggestions were discussed.
God bless you!
Have a nice day!
References
