Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Ok you first question:I give you a example which may be better understanding! <img src="https://i.stack.imgur.com/UvLpU.jpg" alt="enter image description here"></p> <pre><code>#include&lt;iostream&gt; using namespace std; class Base1 { public: int ibase1; Base1():ibase1(10) {} virtual void f() { cout &lt;&lt; "Base1::f()" &lt;&lt; endl; } virtual void g() { cout &lt;&lt; "Base1::g()" &lt;&lt; endl; } virtual void h() { cout &lt;&lt; "Base1::h()" &lt;&lt; endl; } }; class Base2 { public: int ibase2; Base2():ibase2(20) {} virtual void f() { cout &lt;&lt; "Base2::f()" &lt;&lt; endl; } virtual void g() { cout &lt;&lt; "Base2::g()" &lt;&lt; endl; } virtual void h() { cout &lt;&lt; "Base2::h()" &lt;&lt; endl; } }; class Base3 { public: int ibase3; Base3():ibase3(30) {} virtual void f() { cout &lt;&lt; "Base3::f()" &lt;&lt; endl; } virtual void g() { cout &lt;&lt; "Base3::g()" &lt;&lt; endl; } virtual void h() { cout &lt;&lt; "Base3::h()" &lt;&lt; endl; } }; class Derive : public Base1, public Base2, public Base3 { public: int iderive; Derive():iderive(100) {} virtual void f() { cout &lt;&lt; "Derive::f()" &lt;&lt; endl; } virtual void g1() { cout &lt;&lt; "Derive::g1()" &lt;&lt; endl; } }; </code></pre> <p>This the memory rank of a derived class which implemented three base classes base1, base2, base3, where you :</p> <pre><code>Base1 *p1 = new Derive(); Base2 *p2 = new Derive(); Base3 *p3 = new Derive(); </code></pre> <p>p1 will point the vtale1, p2 will point to vtable2, p3 will point to vtable3, If you call some virtual function it will find the very virtual table and get the address!</p> <p>In your code:</p> <pre><code>X *h = new Y; </code></pre> <p>h will point to beginning position of the memory of Y, which is the virtual table of X,he will find the address of <code>abc()</code> which implemented in Y!</p> <p>your second question:</p> <p>The complier will consider the member function as the normal function, so it put the address of member function in the <code>code section</code>,so it does not occupied the memory!!</p> <p>If you want to read the virtual table you can try like this:which is I tried in my example in gcc4.7</p> <pre><code>typedef void(*Func)(void); Derive d; int **pd = (int **)(&amp;d); int i = 0; while(i &lt; 4) { Func f = (Func)pd[0][i]; f(); i++; } int s = (int)(pd[1]); cout &lt;&lt; s &lt;&lt; endl; i = 0; cout &lt;&lt; "===============================================" &lt;&lt; endl; while(i &lt; 3) { Func f = (Func)pd[2][i]; f(); i++; } s = (int)(pd[3]); cout &lt;&lt; s &lt;&lt; endl; cout &lt;&lt; "===============================================" &lt;&lt; endl; i = 0; while(i &lt; 3) { Func f = (Func)pd[4][i]; f(); i++; } s = (int)(pd[5]); cout &lt;&lt; s &lt;&lt; endl; s = (int)(pd[6]); cout &lt;&lt; s &lt;&lt; endl; </code></pre> <p>and you will get the result as follow:</p> <pre><code> Derive::f() Base1::g() Base1::h() Derive::g1() 10 =============================================== Derive::f() Base2::g() Base2::h() 20 =============================================== Derive::f() Base3::g() Base3::h() 30 100 </code></pre>
    singulars
    1. This table or related slice is empty.
    1. POTrouble with understanding virtual functions
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USminicaptain
    1. USminicaptain
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload