Virtual method table
（重定向自Virtual table）
A virtual method table (VMT), virtual function table, virtual call table, dispatch table, vtable, or vftable is a mechanism used in a programming language to support dynamic dispatch (or run-time method binding).
Whenever a class defines a virtual function (or method), most compilers add a hidden member variable to the class which points to an array of pointers to (virtual) functions called the virtual method table (VMT or Vtable). These pointers are used at runtime to invoke the appropriate function implementations, because at compile time it may not yet be known if the base function is to be called or a derived one implemented by a class that inherits from the base class.