C/the.ansi.c.programming.language/notes.accompany.ansi.c/sx8i.html

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   9 <title>section 5.9: Pointers vs. Multi-dimensional Arrays</title>
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  15 <H2>section 5.9: Pointers vs. Multi-dimensional Arrays</H2>
  16
  17 <p>Actually, some people
  18 (and not just newcomers)
  19 are sometimes
  20 confused about the difference
  21 between a one-dimensional array and a single pointer,
  22 too;
  23 moving to two-dimensional arrays, arrays of pointers,
  24 and pointers to pointers only makes things worse.
  25 (But don't lose heart:
  26 if you pay attention and keep your head screwed on straight,
  27 you should be able to keep the differences clearly in mind.)
  28 </p><p>The adjective ``syntactically'' in the paragraph at the bottom of
  29 the page is significant:
  30 after saying
  31 <pre>   int *b[10];
  32 </pre>an immediate reference to <TT>b[3][4]</TT>
  33 would <em>not</em> be completely legal.
  34 It wouldn't be a syntax error or anything,
  35 but when the compiler tried to fetch the third pointer
  36 and then the fourth integer pointed to,
  37 it would go off into deep space,
  38 because there <em>isn't</em> a third pointer
  39 yet
  40 and it doesn't point anywhere.
  41 </p><p>You might want to draw a picture of the data structures that would result
  42 ``[a]ssuming that each element of <TT>b</TT>
  43 does point to a twenty-element array,''
  44 and verify that there are ``200 <TT>int</TT>s set aside,
  45 plus ten cells for the pointers.''
  46 (The picture will be similar to the one on the next page.)
  47 </p><p>Actually, I'm not sure if having rows of different lengths
  48 is the only important advantage of using a pointer array.
  49 Another is that the size of the arrays
  50 (as we'll see later)
  51 can be decided at run-time;
  52 another is that the pointers make certain manipulations easier
  53 (such as the sorting example we worked through in section 5.6).
  54 </p><p>page 114
  55 </p><p>Do study the pictures on this page carefully,
  56 and make sure you understand
  57 the representations of the <TT>name</TT> and <TT>aname</TT> arrays
  58 and how they differ.
  59 (You might want to refer back
  60 to the similar discussion of <TT>pmessage</TT> and <TT>amessage</TT>
  61 on page 104 in section 5.5.)
  62 </p><hr>
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  71 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
  72 // <a href="copyright.html">Copyright</a> 1995, 1996
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