Friday, January 27, 2006

finally clause in C++

The following puzzle was suggested by my former colleague Thomas. Explain how to port a finally clause as used in Java to C++ without loosing its semantics.
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3 comments:

Unknown said...

Generally, finally clauses are done using stack objects in C++. I.e. if the code in Java was:

int oldFoo = getFoo();
try {
setFoo(15);
doSomethingThatMayFail();
}
catch( ... )
{
...
}
finally
{
setFoo(oldFoo);
}

You'd write a class

class StFooChanger
{
public:
int mSavedFoo;

StFooChanger( int newVal )
{
mSavedFoo = getFoo();
setFoo( newVal );
}
~StFooChanger()
{
setFoo(mSavedFoo);
}
};

and then use it like:

StFooChanger changer(15);
try {
doSomethingThatMayFail();
}
catch( ... )
{
...
}

And the destructor of changer will take care of setting things back, whether an exception is raised or not. Cookie?

9:48 AM
Unknown said...
This comment has been removed by the author.
9:49 AM
Robert said...

Yes, stack objects is a good way to go here. Though you could write it down a little more Java-like. But since this was not explicitly requested you may take your cookie. Google websites have a spare one all the time. ;-)

10:14 AM

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