C ++ derived class Object Memory Layout

• Question:

Class C inherits from the base class A and base class B. Now there is an object of class C which converts its address to the base class A pointer and the base class B pointer respectively, are the values of these two pointers equal?

• Answer:

Not equal.

• Explanation:

As you can see, the derived class Object puts the information about each base class together in the memory and stores its own members. The values of class C object addresses after being converted to Class A and Class B pointers are shown in.

• The following is a verification program:

// Cpp_learning.cpp: defines the entry point for the console application. <br/> // </P> <p> # include <iostream> <br/> using namespace STD; <br/> Class A <br/>{< br/> Public: <br/> int A; <br/> int B; <br/> virtual void message () <br/>{< br/> cout <"base a" <Endl; <br/>}< br/> }; </P> <p> Class B <br/> {<br/> Public: <br/> int C; <br/> int D; <br/> virtual void message () <br/>{< br/> cout <"Base B" <E NDL; <br/>}</P> <p >}; </P> <p> Class C: Public, public B <br/>{< br/> Public: <br/> int e; <br/> virtual void message () <br/>{< br/> cout <"derive C" <Endl; <br/>}< br/> }; </P> <p> void Casta (A) <br/> {<br/> cout <". A = "<. A <Endl; <br/> cout <". B = "<. B <Endl; <br/>. message (); </P> <p >}</P> <p> void castb (B) <br/>{< br/> cout <"B. C = "<B. c <Endl; <br/> cout <"B. D = "<B. d <Endl; <Br/> B. message (); <br/>}</P> <p> void castaref (A & A) <br/>{< br/> cout <". A = "<. A <Endl; <br/> cout <". B = "<. B <Endl; <br/>. message (); </P> <p >}</P> <p> void castbref (B & B) <br/> {<br/> cout <"B. C = "<B. c <Endl; <br/> cout <"B. D = "<B. d <Endl; <br/> B. message (); <br/>}</P> <p> int main () <br/>{< br/> C; <br/> C. a = 1; <br/> C. B = 2; <br/> C. C = 3; <br/> C. D = 4; <br/> C. E = 5; <Br/> C C1; <br/> A * pA = (A *) & C; <br/> B * pb = (B *) & C; <br/> A & A = C; <br/> B & B = C; </P> <p> If (INT) pA = (INT) Pb) <br/>{< br/> cout <"Pa = Pb" <Endl; <br/>}< br/> else <br/>{< br/> cout <"Pa! = Pb "<Endl; <br/>}</P> <p> If (INT) & A = (INT) & B) <br/>{ <br/> cout <"& A = & B" <Endl; <br/>}< br/> else <br/>{< br/> cout <"&! = & B "<Endl; <br/>}</P> <p> If (INT) & A = (INT) Pa) <br/>{< br/> cout <"& A = PA" <Endl; <br/>}< br/> else <br/>{< br/> cout <"&! = PA "<Endl; <br/>}</P> <p> If (INT) & B = (INT) Pb) <br/>{< br/> cout <"& B = Pb" <Endl; <br/>}< br/> else <br/>{< br/> cout <"& B! = Pb "<Endl; <br/>}</P> <p> Casta (c); <br/> castb (C ); <br/> castaref (c); <br/> castbref (c); <br/> cout <"Pa =" <(INT) Pa <Endl; <br/> cout <"PB =" <(INT) Pb <Endl; <br/> cout <"& C. E = "<(INT) & C. E <Endl; <br/> cout <"sizeof A =" <sizeof (a) <Endl; <br/> cout <"sizeof B =" <sizeof (B) <Endl; <br/> cout <"sizeof c =" <sizeof (c) <Endl; </P> <p> return 0; <br/>}

• Execution result:

Pa! = Pb
&! = & B
& A = pa
& B = Pb
A. A = 1
A. B = 2
Base
B. C = 3
B. D = 4
Base B
A. A = 1
A. B = 2
Derive C
B. C = 3
B. D = 4
Derive C
Pa = 2293536
Petabytes = 2293548
& Amp; C. E = 2293560
Sizeof A = 12
Sizeof B = 12
Sizeof c = 28