struct Foo
{
  int a;
  uint b;
};

void boo(Foo* foo, uint foo_size);

  // Ver = 0
struct Foo_v0
{
  int a;
  uint b;
};
  // Ver = 1
struct Foo_v1
{
  int a;
  uint b;
  uint c;
};

class Foo {};

class Foo_v0 : public Foo
{
public:
   int a;
   uint b;
};

class Foo_v1 : public Foo
{
public:
   int a;
   uint b;
   uint c;
};

class Foo
{
public:
   int a;
   uint b;
};

class Foo_v0 : public Foo
{
};

class Foo_v1 : public Foo
{
public:
   uint c;
;

int boo(Foo* foo, uint foo_size);
// вызов
Foo_v0 foo;
res = boo(&foo, sizeof(foo));

А>struct Foo
А>{
А>  int a;
А>  uint b;
А>};
А>

А>void boo(Foo* foo, uint foo_size);
А>

class IFoo
{
   IFoo* queryInterface(char const*);
};

class Foo : public IFoo
{
   IFoo* queryInterface(char const* name)
   {
       return strcmp(name, "Foo") ? NULL : this;
   }
};

class Foo2 : public IFoo
{
   IFoo* queryInterface(char const* name)
   {
       return strcmp(name, "Foo.2") ? NULL : this;
   }
};


void boo(IFoo* foo)
{
    if (IFoo* f = foo.queryInterface("Foo"))
    {
        // do something        
    }
    else if (IFoo* f = foo.queryInterface("Foo.2"))
    {
        // do something
    }
    else
    { 
         throw std::runtime_error("The interface is not supported.");
    }
}