Cast QVariant to int

TomNow99

Hello,

I have QVariant with int value on it:

QVariant variant(3);

Now I would like to do something like that:

int value = variant;

Of course I can't. I can't cast from QVariant to int. So I can use method toInt() from QVariant. But I would like to do that dynamically. I try:

int value = ( variant.type() ) variant;

Of course this doesn't work, but I would like something like that. Is there any way to do that?

JonB

@TomNow99
But there isn't, for the same reason. QDataStream operator << needs to know the type at compile time, just the same question as before. Because we are C++ and that is a strongly typed language. Unless you're willing to stream it as a QVariant, which is not what you want.

At the end of the day you can write a method just like you've shown just with the necessary ifs/switch for all the QVariant types you want to handle, which might be a dozen? Once you've written the method once, it's done.

mrjj

@TomNow99
Hi
Af far as i know - you cant really do that dynamic.

Also if
int value = ( variant.type() ) variant;
did work, you would convert all to int which might not always be what you wanted.

Can I ask what you need this for ?

JonB

@TomNow99 said in Cast QVariant to int:

int value = ( variant.type() ) variant;

It seems to me the whole point of C++ typing is that you simply cannot do anything like this.....

TomNow99

@JonB

@mrjj Of course I know that

int value = ( variant.type() ) variant;

doesn't work and I know about "int" :)

I have many QVariant variables and I would like to add them to QByteArray. But I can't add them to this Array like QVariant. I need to add them like int/char/double.

So I would like do something like:

QByteArray byte;
QDataStream stream(&byte, QIODevice::WriteOnly);


for( auto element: variants )
{
    stream<<element; // here I have to cast QVariant to int/char/double
}

Of course I can do something like:

if(metatype of element == metatype int )
{
    stream<<element.toInt();
}
else if(metatype of element == metatype double )
{
    stream<<element.toDouble();
}

But maybe is shorter solution?

JonB

@TomNow99
But there isn't, for the same reason. QDataStream operator << needs to know the type at compile time, just the same question as before. Because we are C++ and that is a strongly typed language. Unless you're willing to stream it as a QVariant, which is not what you want.

At the end of the day you can write a method just like you've shown just with the necessary ifs/switch for all the QVariant types you want to handle, which might be a dozen? Once you've written the method once, it's done.