The answer to "why 24" will be that allocating a single byte, or 4, probably doesn't make sense with the amount of bookkeeping data involved. That malloc implementation is probably just making the minimum size be 24, quite possibly for alignment reasons.

C99 has variable-length arrays (VLAs), which would allow this, where gizmo would be on the stack and evaporate on do_something's return: 

void do_something(int n) {
  struct acme gizmo[n];
  int i;
  for (i=0; i<n; i++) { /* do stuff */ }
}

[download]

The code above has a syntax error: gizmo* = (acme*)malloc(sizeof(acme) * N) has an unnecessary "*" after "gizmo".

In reply to Re^2: OT: Why does malloc always give me 24? by etj
in thread OT: Why does malloc always give me 24? [SOLVED] by karlgoethebier

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.