How do you manually call constructors in C++?

e.g. if you have allocated an array of class instances but weren't allowed to use new(), and the classes have stuff in the constructor which is important, but you can't move it into an .Init() function because they are other classes within the private: data of the class.
(It's great working with other peoples code isn't it!)


I tried doing
for (i=0;i.MyClass();

But no luck:
"error C2274: 'function-style cast' : illegal as right side of '.' operator"


Weirdly:
for (i=0;i.~MyClass();
works!


You learn something old everyday...

>
>
> How do you manually call constructors in C++?
>
> e.g. if you have allocated an array of class instances but weren't allowed to
> use new(), and the classes have stuff in the constructor which is important, but
> you can't move it into an .Init() function because they are other classes within
> the private: data of the class.
> (It's great working with other peoples code isn't it!)
>
>
> I tried doing
> for (i=0;i.MyClass();
>
> But no luck:
> "error C2274: 'function-style cast' : illegal as right side of '.' operator"

You want.. placement new!

For example,

void* mem=malloc(sizeof(FooClass));

FooClass* p = new(mem) FooClass(999);

To delete the object, as you found you can call destructors, then just free the memory.
>
>
> Weirdly:
> for (i=0;i.~MyClass();
> works!
>
>
> You learn something old everyday...
>

> >
> >
> > How do you manually call constructors in C++?
> >
> > e.g. if you have allocated an array of class instances but weren't allowed to
> > use new(), and the classes have stuff in the constructor which is important,
> but
> > you can't move it into an .Init() function because they are other classes
> within
> > the private: data of the class.
> > (It's great working with other peoples code isn't it!)
> >
> >
> > I tried doing
> > for (i=0;i.MyClass();
> >
> > But no luck:
> > "error C2274: 'function-style cast' : illegal as right side of '.' operator"
>
> You want.. placement new!
>
> For example,
>
> void* mem=malloc(sizeof(FooClass));
>
> FooClass* p = new(mem) FooClass(999);
>
> To delete the object, as you found you can call destructors, then just free the
> memory.


Brilliant! Thanks, that's just what I was after. You learn something new everyday

In fact I learnt two new things: strrchr is an ANSI function to find the last occurance of a character. Hurrah! The amount of times I needed that and ending up writing my own tacky routine :p
Now if only Microsoft had used it in Outlook...

> >
> >
> > Weirdly:
> > for (i=0;i.~MyClass();
> > works!
> >
> >
> > You learn something old everyday...
> >
>


You learn something old everyday...