[Interest] QStringList, takeFirst and order of execution

[Giuseppe D'Angelo]

Il 11/11/2013 13:37, Samuel Gaist ha scritto:
> Hi,
>
> I have been experiencing a strange behavior with QStringList and the order of execution of takeFirst.
>
> The following code:
>
> QString line = file.readLine();  // line contains "46 71\n"
> QStringList lineData = line.split(); // lineData contains ("46", "71\n")
> qDebug() << lineData.takeFirst() << lineData.takeFirst();

I've already explained this in the past but I can't find the relevant 
email. This last line is parsed as

> operator<<( operator<<( qDebug(), lineData.takeFirst() ) , lineData.takeFirst() )

(operator<< is left associative).

Take the outer operator<<. C++ does not define the order of evaluating 
its parameters. That means that either lineData.takeFirst() can be 
called before evaluating the inner operator<<, or vice-versa. Depending 
on what the compiler chooses to do, you'll have a different result.

HTH,
-- 
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Software Engineer
KDAB (UK) Ltd., a KDAB Group company
Tel. UK +44-1738-450410, Sweden (HQ) +46-563-540090
KDAB - Qt Experts - Platform-independent software solutions

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