Re: How Type-Safe is C++?

Lance Diduck <>
Mon, 26 May 2008 23:01:07 CST
On May 26, 6:02 pm, Tjark Weber <> wrote:


what are the language constructs that break type safety in C++?

After looking at the standard, my impression is that most constructs
which are potentially unsafe (in particular casts, pointer arithmetic,
unions) have defined behavior only as long as they are used in a type-
safe way. The memcpy function seems to be an exception. Are there
any others, e.g. in connection with derived classes?


operator= is one example. I'm not quite sure what the standard says,
but this is sure to break some code, but is perfectly type safe:
class B{
B& operator=(B const&b){
//the typical implementation...
int v;

class D:B{

D& operator=(D const&d){
return *this;
double b;

Then of course you do this:
B*b=new D;
B b2;
b2=*b;//slice, and UDB

Of course,
delete b;//undefined, per the standard
//no virtual dtor


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