Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <blockquote> <p>I can somewhat guarantee that no object would exists in multiple_selection or simple_selection if it is not in object_container first.</p> </blockquote> <p>If you 150% sure, than there is no need for smart ptr.</p> <p>Reason you may need it in this situation is debug, I think. In case you describe - multiple_selection and simple_selection is not <strong>shared_ptr</strong>, but <strong>weak_ptr</strong>.</p> <p>Code with <strong>error</strong>:</p> <pre><code> std::vector&lt;int*&gt; owner_vector; std::vector&lt;int*&gt; weak_vector; int* a = new int(3); owner_vector.push_back(a); weak_vector.push_back(a); std::for_each( owner_vector.begin(), owner_vector.end(), [](int* ptr) { delete ptr; } ); std::for_each( weak_vector.begin(), weak_vector.end(), [](int* ptr) { *ptr = 3; // oops... usage of deleted pointer } ); </code></pre> <p>You can catch it with smart pointers:</p> <pre><code> std::vector&lt;std::shared_ptr&lt;int&gt;&gt; owner_vector; std::vector&lt;std::weak_ptr&lt;int&gt;&gt; weak_vector; { auto a = std::make_shared&lt;int&gt;(); owner_vector.push_back(a); weak_vector.push_back(a); } std::for_each( owner_vector.begin(), owner_vector.end(), [](std::shared_ptr&lt;int&gt;&amp; ptr) { ptr.reset(); // memory delete } ); std::for_each( weak_vector.begin(), weak_vector.end(), [](std::weak_ptr&lt;int&gt;&amp; ptr) { assert(!ptr.expired()); // guarantee to be alive auto shared_ptr = ptr.lock(); *shared_ptr = 3; } ); </code></pre> <p>In last example you will have assert failed, but not undefined/segmentation fault. In not debug case you can disable shared_ptr <strong>overhead</strong>.</p>
    singulars
    1. This table or related slice is empty.
    1. POReplacing raw pointers in vectors with std::shared_ptr
      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. 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
    1. COThanks for the thorough examples. I am adding them to my personal reference file right now. I just commented below that I am sure they won't be used when deleted since every change in the owning vector is followed by empty / setting the borrowers to null. You mention the weak_ptr and I just read the somewhat cryptic (to me) reference... Could that model the "I borrow this resource" relationship?. Kai below suggested keeping the current scheme (tried and true) and I may just do that if that's a reasonable solution. Any tips?. Thanks a lot.
      singulars
      1. PO
      1. USThe Marlboro Man
 

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