Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>It is perfectly safe.</p> <p>The following code sample:</p> <pre><code>#include &lt;iostream&gt; #include &lt;boost/shared_ptr.hpp&gt; int main(int, char**) { boost::shared_ptr&lt;int&gt; a(new int(5)); boost::shared_ptr&lt;const int&gt; b = a; std::cout &lt;&lt; "a: " &lt;&lt; a.use_count() &lt;&lt; std::endl; std::cout &lt;&lt; "b: " &lt;&lt; b.use_count() &lt;&lt; std::endl; return EXIT_SUCCESS; } </code></pre> <p>Compiles and run fine, and is perfectly correct. It outputs:</p> <pre><code>a: 2 b: 2 </code></pre> <p>The two <code>shared_ptr</code> share the same reference counter.</p> <hr> <p>Also:</p> <pre><code>#include &lt;iostream&gt; #include &lt;boost/shared_ptr.hpp&gt; class A {}; class B : public A {}; int main(int, char**) { boost::shared_ptr&lt;A&gt; a(new B()); boost::shared_ptr&lt;B&gt; b = boost::static_pointer_cast&lt;B&gt;(a); std::cout &lt;&lt; "a: " &lt;&lt; a.use_count() &lt;&lt; std::endl; std::cout &lt;&lt; "b: " &lt;&lt; b.use_count() &lt;&lt; std::endl; return EXIT_SUCCESS; } </code></pre> <p>Behave the same way. You must, however <strong>never</strong> build your <code>shared_ptr</code> using a construct like this:</p> <pre><code>boost::shared_ptr&lt;A&gt; a(new B()); boost::shared_ptr&lt;B&gt; b(static_cast&lt;B*&gt;(a.get())); </code></pre> <p><code>a.get()</code> gives the raw pointer and loses all information about reference counting. Doing this, you'll end up with two distinct (not linked) <code>shared_ptr</code> that use the same pointer but different reference counters.</p>
    singulars
    1. This table or related slice is empty.
    1. PODo boost::shared_ptr<T> and boost::shared_ptr<const T> share the reference count?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USereOn
    1. USereOn
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PODo boost::shared_ptr<T> and boost::shared_ptr<const T> share the reference count?
      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. VTAcceptedByOriginator
    1. COThanks, you are perfectly right. I had a completely different misunderstanding along the lines of ybungalobill's example. Thank you both!
      singulars
      1. PO
      1. USlytenyn
    2. COI was about to post a question on casting shared_pointer but got the answer here. Thx.
      singulars
      1. PO
      1. USrjoshi
 

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