What is the dynamic type of the object allocated by malloc?

Question

The C++ standard refers to the term "dynamic type" (and the C standard refers to "effective type" in the similar context), for example

<

Answer 1

As per 1.3.7 in C++11 standard,

dynamic type glvalue type of the most derived object (1.8) to which the glvalue denoted by a glvalue expression refers [Example: if a pointer (8.3.1) p whose static type is “pointer to class B” is pointing to an object of class D, derived from B (Clause 10), the dynamic type of the expression *p is “D.” References (8.3.2) are treated similarly. — end example ]

for an example

class A {}
class B : public A {}
A *a = new B;

the "static" type of a is A * while its dynamic type is B *.

The idea of referencing not the same type comes to protect from something like

class A{}
class B : public A {int x;}
class C : public A {int y;}
A *a = new B;
reinterpret_cast(a)->x;

which may lead to undefined behavior.

void * does not point to an object, but the distinction between dynamic and declaration type makes sense only for objects.