📄 atl under the hood - part 2.mht
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<SPAN class=3Dcpp-keyword>class</SPAN> Base {
<SPAN class=3Dcpp-keyword>public</SPAN>:
Base() {
cout << <SPAN class=3Dcpp-string>"In Base"</SPAN> << =
endl;
cout << <SPAN class=3Dcpp-string>"Virtual Pointer =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN> << endl;
cout << <SPAN class=3Dcpp-string>"Address of Vtable =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN class=3Dcpp-keyword>this</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 1st =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>0</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 2nd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>1</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 3rd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>2</SPAN>) =
<< endl;
cout << endl;
}
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f1() { cout << <SPAN =
class=3Dcpp-string>"Base::f1"</SPAN> << endl; }
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f2() { cout << <SPAN =
class=3Dcpp-string>"Base::f2"</SPAN> << endl; }
};
<SPAN class=3Dcpp-keyword>class</SPAN> Drive : <SPAN =
class=3Dcpp-keyword>public</SPAN> Base {
<SPAN class=3Dcpp-keyword>public</SPAN>:
Drive() {
cout << <SPAN class=3Dcpp-string>"In Drive"</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Virtual Pointer =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN> << endl;
cout << <SPAN class=3Dcpp-string>"Address of Vtable =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN class=3Dcpp-keyword>this</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 1st =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>0</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 2nd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>1</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 3rd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>2</SPAN>) =
<< endl;
cout << endl;
}
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f1() { cout << <SPAN =
class=3Dcpp-string>"Drive::f1"</SPAN> << endl; }
};
<SPAN class=3Dcpp-keyword>int</SPAN> main() {
Drive d;
<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>The output of this program is <PRE>In Base
Virtual Pointer =3D 0012FF7C
Address of Vtable =3D 0046C0E0
Value at Vtable 1st entry =3D 004010F0
Value at Vtable 2nd entry =3D <SPAN class=3Dcpp-literal>00401145</SPAN>
Value at Vtable 3rd entry =3D <SPAN class=3Dcpp-literal>00000000</SPAN>
In Drive
Virtual Pointer =3D 0012FF7C
Address of Vtable =3D 0046C0C8
Value at Vtable 1st entry =3D 0040121C
Value at Vtable 2nd entry =3D <SPAN class=3Dcpp-literal>00401145</SPAN>
Value at Vtable 3rd entry =3D <SPAN class=3Dcpp-literal>00000000</SPAN>
</PRE>The output of this program shows that the base class's virtual=20
function is not overridden in drive class then drive class =
constructor=20
doesn't do anything with that entry in virtual function.=20
<P>Now invite pure virtual function in this game too and see the =
behavior=20
of it. Take a look at the following program=20
<H3>Program 27</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
<iostream></SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;
<SPAN class=3Dcpp-keyword>class</SPAN> Base {
<SPAN class=3Dcpp-keyword>public</SPAN>:
Base() {
cout << <SPAN class=3Dcpp-string>"In Base"</SPAN> << =
endl;
cout << <SPAN class=3Dcpp-string>"Virtual Pointer =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN> << endl;
cout << <SPAN class=3Dcpp-string>"Address of Vtable =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN class=3Dcpp-keyword>this</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 1st =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>0</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 2nd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>1</SPAN>) =
<< endl;
cout << endl;
}
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f1() =3D <SPAN =
class=3Dcpp-literal>0</SPAN>;
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f2() =3D <SPAN =
class=3Dcpp-literal>0</SPAN>;
};
<SPAN class=3Dcpp-keyword>class</SPAN> Drive : <SPAN =
class=3Dcpp-keyword>public</SPAN> Base {
<SPAN class=3Dcpp-keyword>public</SPAN>:
Drive() {
cout << <SPAN class=3Dcpp-string>"In Drive"</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Virtual Pointer =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN> << endl;
cout << <SPAN class=3Dcpp-string>"Address of Vtable =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN class=3Dcpp-keyword>this</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 1st =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>0</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 2nd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>1</SPAN>) =
<< endl;
cout << endl;
}
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f1() { cout << <SPAN =
class=3Dcpp-string>"Drive::f1"</SPAN> << endl; }
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f2() { cout << <SPAN =
class=3Dcpp-string>"Drive::f2"</SPAN> << endl; }
};
<SPAN class=3Dcpp-keyword>int</SPAN> main() {
Drive d;
<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>The output of this program is little bit different in debug and=20
release mode. Here is the output of the debug mode <PRE>In Base
Virtual Pointer =3D 0012FF7C
Address of Vtable =3D 0046C0BC
Value at Vtable 1st entry =3D 00420CB0
Value at Vtable 2nd entry =3D 00420CB0
In Drive
Virtual Pointer =3D 0012FF7C
Address of Vtable =3D 0046C0A4
Value at Vtable 1st entry =3D <SPAN class=3Dcpp-literal>00401212</SPAN>
Value at Vtable 2nd entry =3D 0040128F
</PRE>And here is the output in the release Mode <PRE>In Base
Virtual Pointer =3D 0012FF80
Address of Vtable =3D 0042115C
Value at Vtable 1st entry =3D 0041245D
Value at Vtable 2nd entry =3D 0041245D
In Drive
Virtual Pointer =3D 0012FF80
Address of Vtable =3D <SPAN class=3Dcpp-literal>00421154</SPAN>
Value at Vtable 1st entry =3D <SPAN class=3Dcpp-literal>00401310</SPAN>
Value at Vtable 2nd entry =3D <SPAN class=3Dcpp-literal>00401380</SPAN>
</PRE>To better understand change a program little bit and try to call=20
virtual function from function pointer.=20
<H3>Program 28</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
<iostream></SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;
<SPAN class=3Dcpp-keyword>typedef</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN>(*Fun)();
<SPAN class=3Dcpp-keyword>class</SPAN> Base {
<SPAN class=3Dcpp-keyword>public</SPAN>:
Base() {
cout << <SPAN class=3Dcpp-string>"In Base"</SPAN> << =
endl;
cout << <SPAN class=3Dcpp-string>"Virtual Pointer =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN> << endl;
cout << <SPAN class=3Dcpp-string>"Address of Vtable =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN class=3Dcpp-keyword>this</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 1st =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>0</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 2nd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>1</SPAN>) =
<< endl;
=20
<SPAN class=3Dcpp-comment>// try to execute first virtual =
function</SPAN>
Fun pFun =3D (Fun)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>0</SPAN>);
pFun();
cout << endl;
}
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f1() =3D <SPAN =
class=3Dcpp-literal>0</SPAN>;
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f2() =3D <SPAN =
class=3Dcpp-literal>0</SPAN>;
};
<SPAN class=3Dcpp-keyword>class</SPAN> Drive : <SPAN =
class=3Dcpp-keyword>public</SPAN> Base {
<SPAN class=3Dcpp-keyword>public</SPAN>:
Drive() {
cout << <SPAN class=3Dcpp-string>"In Drive"</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Virtual Pointer =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN> << endl;
cout << <SPAN class=3Dcpp-string>"Address of Vtable =3D =
"</SPAN> << (<SPAN class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN class=3Dcpp-keyword>this</SPAN> =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 1st =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>0</SPAN>) =
<< endl;
cout << <SPAN class=3Dcpp-string>"Value at Vtable 2nd =
entry =3D "</SPAN> << (<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*((<SPAN =
class=3Dcpp-keyword>int</SPAN>*)*(<SPAN =
class=3Dcpp-keyword>int</SPAN>*)<SPAN =
class=3Dcpp-keyword>this</SPAN>+<SPAN class=3Dcpp-literal>1</SPAN>) =
<< endl;
cout << endl;
}
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f1() { cout << <SPAN =
class=3Dcpp-string>"Drive::f1"</SPAN> << endl; }
<SPAN class=3Dcpp-keyword>virtual</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> f2() { cout << <SPAN =
class=3Dcpp-string>"Drive::f2"</SPAN> << endl; }
};
<SPAN class=3Dcpp-keyword>int</SPAN> main() {
Drive d;
<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>Now the behavior of program is different in debug and release =
Mode.=20
In Debug mode it display run time error dialog box=20
<P>
<CENTER><IMG height=3D188=20
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