C + + Note memory alignment

1#include <iostream>2 3 #pragmaPack (4)4 5 structa{6 A () {}7~A () {}8     intM1;//4 bytes9     intm2; 4 bytesTen }; One structb:a{ A B () {} -~B () {} -     intM1;//4 bytes the     Charm2; -     Static Charm3; - }; - structc{ + C () {} -     Virtual~C () {}//64-bit system is 8 bytes//32-bit system is 4 bytes +     intM1; 4 bytes A      Shortm2; at }; -  - intMain () - { -Std::cout <<sizeof(A) <<Std::endl; -Std::cout <<sizeof(B) <<Std::endl; inStd::cout <<sizeof(C) <<Std::endl; -Std::cout <<sizeof(int*) <<Std::endl; to  +     return 0; -}

• In a 32-bit system

sizeof (A) = 4 + 4 = 8 byte

sizeof (B) = sizeof (A) + 4 + 1 (requires memory alignment) = Byte

sizeof (C) = virtual function pointer size 4 + 4 + 2 (requires memory alignment) = Byte

• In a 64-bit system

sizeof (A) = 4 + 4 = 8 byte

sizeof (B) = sizeof (A) + 4 + 1 (requires memory alignment) = Byte

sizeof (C) = virtual function pointer size 8 + 4 + 2 (requires memory alignment) = Byte

C + + Note memory alignment