Computes the bytes occupied by the C + + class (that is, sizeof)

In a class, if there is nothing, the class consumes 1 bytes, and once there are other space-occupying members in the class, the 1 bytes are not counted, such as a class with only one int that takes 4 bytes instead of 5 bytes. If there is only a member function, it is still only 1 bytes, because the class function does not occupy space. virtual function Because there is a virtual function table, requires 4 bytes, the data member object if the pointer is 4 bytes, note that there is byte alignment, if it is 13 bytes, it is rounded up to 16 bytes of space. Need to note:

1 to find out if there is a virtual function table, +4
2 static member variables belong to the class domain and are not counted into the object +0
3 God horse members do not have a class, or only member functions +1
4 Note the Alignment rule

Example:

classctest{ Public: CTest (): M_chdata (' \0'), M_ndata (0)        {        }        Virtual voidMem_fun () {}Private:        CharM_chdata; intM_ndata; Static CharS_chdata;};CharCtest::s_chdata= ' \0’;

(1) What is the value of sizeof (CTest) If you press 4 bytes? (2) What is the value of sizeof (CTest) If you press 1 bytes? Answers: 12 and 9

Computes the bytes occupied by the C + + class (that is, sizeof)