markww wrote:
Hi,
Can someone explain to me what static and dynamic dispatch are and what
the difference is between the two? Do this even occurr in C++?
Thanks
In the context of C++, "dispatch" is just a fancy name for calling a
member function. A "static" dispatch is one where all the type
information needed to decide which function to call is known at compile
time. Consider the following example:
#include <iostream>
class A
{
public:
void f() const { std::cout << "A::f()" << std::endl ; }
} ;
class B
{
public:
void f() const { std::cout << "B::f()" << std::endl ; }
} ;
int main()
{
A a ;
B b ;
a.f() ;
b.f() ;
}
Here, the compiler has all the type information needed to figure out
which function "f" to call in each case. In the first call, A::f is
called, and in the second, B::f is called.
Dynamic dispatching is needed when it cannot be determined until runtime
which function to call. In C++, this is implemented using virtual
functions. Consider the following:
#include <iostream>
class base
{
public:
virtual void f() const = 0 ;
virtual ~base() {}
} ;
class A : public base
{
public:
virtual void f() const { std::cout << "A::f()" << std::endl ; }
} ;
class B : public base
{
public:
virtual void f() const { std::cout << "B::f()" << std::endl ; }
} ;
void dispatch(const base & x)
{
x.f() ;
}
int main()
{
A a ;
B b ;
dispatch(a) ;
dispatch(b) ;
}
The line "x.f() ;" gets executed twice, but a different function gets
called each time.
--
Alan Johnson
