On segunda-feira, 11 de novembro de 2013 13:37:20, Samuel Gaist wrote: > Hi, > > I have been experiencing a strange behavior with QStringList and the order > of execution of takeFirst.
> qDebug() << lineData.takeFirst() << lineData.takeFirst();
The problem is not takeFirst.
> behaves differently on two computers.
Correct. You have undefined behaviour.
Both calls to takeFirst() are in the same "sequence-point". That means the
compiler is allowed to execute in any order.
It would be the same if you had written:
f(lineData.takeFirst(), lineData.takeFirst());
> qDebug() << lineData.takeFirst();
> qDebug() << lineData.takeFirst();
>
> The order is correct on both of them.
>
> What could explain the difference ?
In the second case, there are two sequence points (they are separated by a ;).
In C++11-speak, the first line of the second example is guaranteed to "happens-
before" the second line. In the first example, there's no "happens-before",
therefore any one can happen before the other, or after.
--
Thiago Macieira - thiago.macieira (AT) intel.com
Software Architect - Intel Open Source Technology Center
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