cpp类内存布局

#include <iostream>

class A
{
public:
    A() : c(0)
    {
        std::cout << "A::A()" << std::endl;
        func2();
    };
    void func2() { std::cout <<"A::func2()" << std::endl; };
private:
    int c;
};

int main(void)
{
    A a1;
    A a2;
    
    return 0;
}

GNU gdb (Ubuntu 12.1-0ubuntu1~22.04) 12.1
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Reading symbols from ./a.out...
(gdb) b 22
Breakpoint 1 at 0x11fc: file basic.cpp, line 22.
(gdb) run
Starting program: /mnt/work/cs-note-src/src/cpp/memory/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
A::A()
A::func2()
A::A()
A::func2()

Breakpoint 1, main () at basic.cpp:22
22          return 0;
(gdb) info vtbl a1
This object does not have a virtual function table
(gdb)
This object does not have a virtual function table
(gdb) p a
$1 = {i = {0, 1045149306}, x = 1.2904777690891933e-08, d = 1.2904777690891933e-08}
(gdb) p a1
$2 = {c = 0}
(gdb) p a2
$3 = {c = 0}
(gdb) p &a1
$4 = (A *) 0x7fffffffe250
(gdb) p &a2
$5 = (A *) 0x7fffffffe254
(gdb) p typeid(a1)
could not find typeinfo symbol for 'A'
(gdb) info address A::func2
Symbol "A::func2()" is a function at address 0x5555555552da.
(gdb) info symbo A::func2
A::func2() in section .text of /mnt/work/cs-note-src/src/cpp/memory/a.out
(gdb)

0x555555557d80        0x000055555555603c
0x555555557d78        0x00007ffff7fa2fa0
0x555555557d70        0x0000555555555366
0x555555557d68        0x00005555555552ea

#include <iostream>

class A
{
public:
    A() : c(0)
    {
        std::cout << "A::A()" << std::endl;
        func2();
    };
    virtual void virtual_func1() { std::cout << "A::virtual_func1()" << std::endl;};
    void func2() { std::cout <<"A::func2()" << std::endl; };
    virtual void virtual_func3() { std::cout << "A::virtual_func3()" << std::endl;};
private:
    int c;
};

class B : public A
{
public:
    B() : a(0), b(0)
    {
        std::cout << "B::B()" << std::endl;
        func2();
    }
    B(int a, int b) : a(a), b(b)
    {
        std::cout << "B::B(int a, int b)" << std::endl;
        func2();
    }
    ~B() { std::cout << "B::~B()" << std::endl; };
    virtual void virtual_fun1() { std::cout <<"B::virtual_fun1()" << std::endl; };
    void func2() { std::cout <<"B::func2()" << std::endl; };
    virtual void virtual_func3() { std::cout << "B::virtual_func3()" << std::endl;};
private:
    int a;
    int b;
};

int main(void)

{
    A a1;
    A a2;
    B b1;
    B b2;

    return 0;

}

(gdb) b 48
Breakpoint 1 at 0x1235: file ./inheritance.cpp, line 48.
(gdb) run
Starting program: /mnt/work/cs-note-src/src/cpp/memory/inheritance
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
A::A()
A::func2()
A::A()
A::func2()
A::A()
A::func2()
B::B()
B::func2()
A::A()
A::func2()
B::B()
B::func2()

Breakpoint 1, main () at ./inheritance.cpp:48
48          return 0;
(gdb) p b1
$1 = {<A> = {_vptr.A = 0x555555557d10 <vtable for B+16>, c = 0}, a = 0, b = 0}
(gdb) p b2
$2 = {<A> = {_vptr.A = 0x555555557d10 <vtable for B+16>, c = 0}, a = 0, b = 0}
(gdb) p &b1
$3 = (B *) 0x7fffffffe210
(gdb) p &b2
$4 = (B *) 0x7fffffffe230
(gdb) p typeid(b1)
$5 = {_vptr.type_info = 0x7ffff7fa3c30 <vtable for __cxxabiv1::__si_class_type_info+16>, __name = 0x55555555607b <typeinfo name for B> "1B"}
(gdb) p typeid(b2)
$6 = {_vptr.type_info = 0x7ffff7fa3c30 <vtable for __cxxabiv1::__si_class_type_info+16>, __name = 0x55555555607b <typeinfo name for B> "1B"}
(gdb) info vtbr b1
Undefined info command: "vtbr b1".  Try "help info".
(gdb) info vtbl b1
vtable for 'B' @ 0x555555557d10 (subobject @ 0x7fffffffe210):
[0]: 0x555555555362 <A::virtual_func1()>
[1]: 0x55555555555e <B::virtual_func3()>
[2]: 0x5555555554e2 <B::virtual_fun1()>
(gdb) p &typeid(b1)
$7 = (gdb_gnu_v3_type_info *) 0x555555557d48 <typeinfo for B>
(gdb) x /16xg 0x555555557d10
0x555555557d10 <_ZTV1B+16>:     0x0000555555555362      0x000055555555555e
0x555555557d20 <_ZTV1B+32>:     0x00005555555554e2      0x0000000000000000
0x555555557d30 <_ZTV1A+8>:      0x0000555555557d60      0x0000555555555362
0x555555557d40 <_ZTV1A+24>:     0x00005555555553de      0x00007ffff7fa3c30
0x555555557d50 <_ZTI1B+8>:      0x000055555555607b      0x0000555555557d60
0x555555557d60 <_ZTI1A>:        0x00007ffff7fa2fa0      0x000055555555607e
0x555555557d70: 0x0000000000000001      0x00000000000001b6
0x555555557d80: 0x0000000000000001      0x00000000000001c5

0x555555557d68       0x000055555555607e  --> typeid(a)  __name = 1A
0x555555557d60       0x00007ffff7fa2fa0  --> typeid(a) _vptr.type_info
0x555555557d58       0x0000555555557d60
0x555555557d50       0x000055555555607b  --> typeid(b)  __name = 1B
0x555555557d48       0x00007ffff7fa3c30  --> typeid(b) _vptr.type_info
0x555555557d40       0x00005555555553de  --> A::virtual_func3()
0x555555557d38       0x0000555555555362  --> A::virtual_func1()
0x555555557d30       0x0000555555557d60
0x555555557d28       0x0000000000000000
0x555555557d20       0x00005555555554e2  --> B::virtual_fun1()
0x555555557d18       0x000055555555555e  --> B::virtual_func3()
0x555555557d10       0x0000555555555362  --> A::virtual_func1()