[Interest] QXmlStreamReader and qDebug()

[Giuseppe D'Angelo]

Il 27/07/2013 00:51, Alexander Syvak ha scritto:
> operator<< is evaluated from the left to the right each time returning
> QDebug object.

That's only half of the story. When in your code you have something like 
this:

     qDebug() << a << b << c;

that will get parsed by the compiler into something like this:

     operator<<(operator<<(operator<<(qDebug(), a), b), c);

Now, what's the order of evaluation of the parameters of topmost 
operator<< call? That's it: C++ leaves it to the implementation.

Under x86, for various reasons (*), arguments gets evaluated right to 
left and pushed to the stack in that order. That means c gets evaluated 
before b, and b before a. If a, b, c are function calls that modify a 
global state, your results will be... unexpected. Which is what you're 
experiencing.

(*) for instance, for being able to implement variadic functions more 
easily: the known parameters are on the top of the stack.

Hope this helps,
-- 
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