Overhead of C++ inheritance with no virtual functions

Question

In C++, what's the overhead (memory/cpu) associated with inheriting a base class that has no virtual functions? Is it as good as a straight up copy+paste of class members?

class a { public:     void get(); protected:     int _px; }  class b : public a {  } 

compared with

class a { public:     void get(); protected:     int _px; }  class b { public:     void get(); protected:     int _px;  } 

Answer 1

There might a be slight memory overhead (due to padding) when using inheritance compared to copy and past, consider the following class definitions:

struct A {   int i;   char c1; };  struct B1 : A {   char c2; };   struct B2 {   int i;   char c1;   char c2; }; 

sizeof(B1) will probably be 12, whereas sizeof(B2) might just be 8. This is because the base class A gets padded separately to 8 bytes and then B1 gets padded again to 12 bytes.

Answer 2

It will take very slightly longer to compile, and there will be no additional runtime overhead. From the optimizer's perspective, non-virtual methods are the same as procedures -- they can be called using only their memory address, without overhead from a virtual method table.