Deserializing QByteArray with known QMetaType::Type into QVariant

user_9987834 0
Viewed 175

I have a QByteArray containing the raw data of a variable.
The QMetaType::Type describing the variable is known.

I want to deserialize this variable into a QVariant

With the following inputs :

QByteArray bytes; // Consider it initialized
QMetaType::Type type; // Same

My attempts so far do not work:

QVariant var{bytes};
var.convert(type); // Does not work, apparently QVariant expects bytes to be a string representation of the variable

QDataStream ds(bytes, QIODevice::ReadOnly);
QVariant var;
ds >> var; // Does not work because bytes does not come from the serialization of a QVariant (especially, it lacks type information)

I cannot change my inputs or output types :

  • The inputs must be of type QByteArray and QMetaType::Type.
  • The output must be of type QVariant

Example :

//Inputs
QByteArray bytes = { 0x12, 0x34, 0x56, 0x78 };
QMetaType::Type type = QMetaType::UInt; // Suppose the size of unsigned int is 4 bytes (could be 2)
// Note: this is an example, in pratice I have to manage many types, including double

//Expected output:
QVariant var = deserialize(bytes, type);
// var.type() == QMetaType::UInt
// var.toUInt() == 305419896 (== 0x12345678)
qt c++
2 Answers

Facing the same problem, I got around constructing the QVariant from a QByteArray directly through its data() method using the provided type id:

QByteArray bytes; // Consider it initialized
QMetaType::Type type; // Same
QVariant result(type.id(),bytes.data());

If the construction fails, you will end up with an invalid QVariant, but so far, for my types, it worked well.

user_74776890

You can write to an unsigned int and then convert it to QVariant:

    const char data[] = { 0x12, 0x34, 0x56, 0x78 };
    QByteArray bytes { QByteArray::fromRawData( data, 4) };

    QDataStream s {&bytes, QIODevice::ReadOnly};
    //write out the data to uint
    unsigned int x{};
    s >> x;

    //create a Qvariant from it
    QVariant var{x};

    qDebug () << "x: " << x;                       //305419896
    qDebug () << "variant: " << var;               //QVariant(uint, 305419896)
    qDebug () << "variant uint: " << var.toUInt(); //305419896

Alternatively you can also directly construct a QVariant:

    auto v = QVariant(bytes.toHex().toUInt());
    //auto v = QVariant(bytes.toUInt());            //this will not work
    qDebug () << "Bytes to uint; " << v.toUInt(); //305419896
user_22794220
Related