virtual function table in c++

what is vfptr？
The follow codes show u it.

#include <stdint.h>#include <iostream>class base {public:  virtual void func1() {    std::cout << "base::func1" << std::endl;  }  virtual void func2() {    std::cout << "base::func2" << std::endl;  }};typedef void (base::*virtual_func)(void);void test_virtual_table() {  char base_addredd[sizeof(base)] = {0};  base *b = new(base_addredd)base;  std::cout <<"The address prealloced is 0x" << std::hex << (intptr_t)base_addredd << std::endl;  std::cout <<"base's address is 0x" << std::hex << b << std::endl;  intptr_t **__vfptr = *reinterpret_cast<intptr_t***>(b);  virtual_func* pfuncs = reinterpret_cast<virtual_func*>(__vfptr);  virtual_func v_func1 = pfuncs[0];  virtual_func v_func2 = pfuncs[1];  std::cout << "function found by vftable" << std::endl;  (b->*v_func1)();  // maybe g++ implement virtual function table differently with virtual studio,this line will crash down  // the messageis: Segmentation fault (core dumped)  // (b->*v_func2)();  std::cout << "end" << std::endl;  void (*p_temp)(void) = (void (*)(void))(&base::func1);  p_temp();  }int main() {  std::cout << "base's size is " << sizeof(base) << std::endl;  test_virtual_table();  return 0;}