Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>You can imagine this code:</p> <pre><code>struct A { void f() {} int int_in_b1; }; int main() { A a; a.f(); return 0; } </code></pre> <p>Being transformed into something like:</p> <pre><code>struct A { int int_in_b1; }; void A__f(A* const this) {} int main() { A a; A__f(&amp;a); return 0; } </code></pre> <p>Calling <em>f</em> is straight-forward because it's non-virtual. (And sometimes for virtual calls, the virtual dispatch can be avoided if the dynamic type of the object is known, as it is here.)</p> <hr> <p>A longer example that will either give you an idea about how virtual functions work or terribly confuse you:</p> <pre><code>struct B { virtual void foo() { puts(__func__); } }; struct D : B { virtual void foo() { puts(__func__); } }; int main() { B* a[] = { new B(), new D() }; a[0]-&gt;foo(); a[1]-&gt;foo(); return 0; } </code></pre> <p>Becomes something like:</p> <pre><code>void B_foo(void) { puts(__func__); } void D_foo(void) { puts(__func__); } struct B_VT { void (*foo)(void); } B_vtable = { B_foo }, D_vtable = { D_foo }; typedef struct B { struct B_VT* vt; } B; B* new_B(void) { B* p = malloc(sizeof(B)); p-&gt;vt = &amp;B_vtable; return p; } typedef struct D { struct B_VT* vt; } D; D* new_D(void) { D* p = malloc(sizeof(D)); p-&gt;vt = &amp;D_vtable; return p; } int main() { B* a[] = {new_B(), new_D()}; a[0]-&gt;vt-&gt;foo(); a[1]-&gt;vt-&gt;foo(); return 0; } </code></pre> <p>Each object only has one vtable pointer, and you can add many virtual methods to the class without affecting object size. (The vtable grows, but this is stored once per class and is not significant size overhead.) Note that I've simplified many details in this example, but it <a href="http://codepad.org/zDkd4LZD" rel="noreferrer">does work</a>: destructors are not addressed (which should additionally be virtual here), it leaks memory, and the <em>__func__</em> values will be slightly different (they're generated by the compiler for the current function's name), among others.</p>
    singulars
    1. This table or related slice is empty.
    1. POC++ class object memory map
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POC++ class object memory map
      singulars
      1. PTQuestion
    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. COThe second example is a few weeks old that I had written, and I see now that I forgot to add *this* pointers, even though they aren't used. If you don't see how to add them, just let me know and I can edit; otherwise I'll keep it the same as the compiled code in the codepad link.
      singulars
      1. PO
      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