On Sun, Feb 27, 2005 at 01:11:11PM -0500, christopher diggins wrote:
From: "Jeff Garland"
At the risk of going against the entrenched dogma here, I'd suggest there are significant cases where this is a good and useful thing to do. I think the original guidance came from Scott Meyers Effective C++ #14 -- make destructors virtual in base classes. The problem I have with this is that I find there are plenty of situations where I might want to add some convenience functions to an stl container in which the subclass has a trivial destructor (eg: no allocated resources)
I am a little confused here, does MySubClass below have a "trivial" destructor?
(N.B. I think the standard uses "trivial destructor" in a stricter sense, meaning that the class *and* all its members and bases have implicitly-declared dtors.)
MySubClass : MyBaseClass { int x; };
I'm not sure what happens to x. I know that with GCC the following code never calls B::~B(), so if it was doing any non-trivial work it would leak: #include <iostream> struct A {}; struct B { ~B() { std::cout << "B::~B\n"; } }; struct C : A { B b; }; int main() { A* p = new C; delete p; } That implies that if you derive from a concrete type with a non-virtual dtor you'd better not add any data members at all. I think don't many people realise that, so I don't think encouraging inheritance from STL containers is a good idea. I might be wrong, but does 12.5/4 mean it is ill-formed to call delete on a pointer-to-base if base::~base is not virtual? jon -- When writing a specialization Be careful about its location Else to make it compile Will be such a trial As to kindle its self-immolation - ISO/IEC 14882/1998 (The C++ Standard)