Home » Tip Bank » C++ » Virtual Functions

Language: C++
Expertise: All

Mar 1, 2000

Generally, compilers can't inline a virtual function call if the it's resolved dynamically. Therefore, declaring a virtual member function inline might seem pointless. However, not every call of a virtual function is resolved dynamically; in some cases, the compiler can resolve the call statically, as if the function weren't virtual. In situations like these, the compiler can also inline the call. For example:

 
  class Base
  {
  public:
    inline virtual int f() { return 0; }
  };

  int main()
  {
    Base b;
    b.f(); // resolved statically; call can be inlined
  }

The invocation of f() is resolved statically because b is not a pointer or a reference. The compiler can also expand the call inline, thereby optimizing the code even further.