Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>With the declaration <code>unsigned long *points</code>, <code>points</code> is a pointer. It points to the beginning of an array. <code>arr[x]</code> is the same as <code>*(arr + x)</code>, so whether <code>arr</code> is an array (in which case, it takes the address of the array, adds <code>x</code>, and dereferences the 'pointer') or a pointer (in which case, it takes the pointer value, adds <code>x</code>, and dereferences the pointer), <code>arr[0]</code> still gets the same array access.</p> <p>In this case, you can't declare <code>points</code> as an array because you're not <em>using</em> it as an array - you're using it as a pointer, which points to an array. A pointer is a shallow copy - if you change the data pointed to by a pointer, it changes the original data. To create a regular array, you'd need to do a deep copy, which would prevent your changes in <code>pointer</code> from affecting the array <code>self</code>, which is ultimately what you want.</p> <p>In fact, you could rewrite the whole thing without <code>points</code>:</p> <pre><code>void SetSpanSeries(Series *self, const Span *src) { if (src-&gt;lo &lt; src-&gt;hi ) { self-&gt;points[0] = src-&gt;lo; self-&gt;points[1] = src-&gt;hi; self-&gt;count = 1; } } </code></pre> <p>As to your second example, yes, <code>points[0].lo</code> is correct. <code>points-&gt;lo</code> would also be correct, so long as you're only accessing <code>points[0]</code>. (Or <code>self-&gt;points[0].lo</code> if you take out <code>points</code> entirely.)</p>
    singulars
    1. This table or related slice is empty.
    1. POBetter way of declaring an array?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USChris Lutz
    1. USChris Lutz
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POBetter way of declaring an array?
      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. CO58 seconds faster _and_ more eloquent. Nice. :)
      singulars
      1. PO
      1. USsarnold
    2. CO"It points to an array" - strictly it points to the first element of the array. This is the same address in memory as the array, but a pointer-to-array is a different type from a pointer-to-an-element-of-that-array. Usually you can conflate the two without causing trouble, but a beginner still needs to know that they're two different things.
      singulars
      1. PO
      1. USSteve Jessop
    3. COThanks you explanation helped be a lot.
      singulars
      1. PO
      1. UShistorystamp
 

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