[gmpi] Re: C++ detail question

On Wed, Mar 02, 2005 at 05:00:52PM -0500, Ron Kuper wrote:
> In VC, the compiler barfs on the cfoo1 assignment.  No surprise since
> it's a member of CFoo, therefore not visible at global scope.

woops, I mean to say "cfoo->cfoo1 = 12345;", of course.

> The call to cfoo->method2() crashes.

as expected.

> /* defined in C */
> struct Foo
> {
>       int foo1;
>       int foo2;
> };
> 
> /* defined in C++ */
> class CFoo : public Foo
> {
> public:
>       int method1(void) { return 0; }
>       virtual int method2(void) { return 0; }
>       int cfoo1;
> };
> 
> void func(struct Foo *foo)
> {
>       CFoo* cfoo = static_cast<CFoo*>(foo);
> 
>       cfoo->method1();        /* safe? */
>       cfoo->method2();        /* not safe */
>       cfoo1 = 12345;          /* not safe */
> }
> 
> 
> My assumption is that it is safe to call CFoo::method1 because the
> compiler will do static binding.  Now, if method1 does something unsafe,
> that's a different story.  Assuming method1 is safe internally, is this
> safe to do?
> 
> It seems pretty clear that CFoo::method2 is illegal, as the CFoo object
> does not have a valid vtable.  Accessing the cfoo1 member is likewise
> bad because it doesn't exist.
> 
> The question is whether it is safe to access method1?
> 
> Specifically, there is a C struct that I want to wrap in C++, including
> a couple of operator methods (needed to be put into a map).  We could
> create a new CFoo and initialize it with the Foo, but it seems like
> there will be a lot of construct/destruct cycles wasted there...
> 
> 
> 
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