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   9 <title>section 6.4: Pointers to Structures</title>
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  15 <H2>section 6.4: Pointers to Structures</H2>
  16
  17 <p>The bulk of this section illustrates how to rewrite the
  18 <TT>binsearch</TT> function
  19 (which we've already been glossing over)
  20 in terms of pointers instead of arrays
  21 (an exercise which we've
  22 been downplaying).
  23 There are a few important points towards the end of the section,
  24 however.
  25 </p><p>page 138
  26 </p><p>When we began talking about pointers and arrays,
  27 we said that it was important never to access outside of the
  28 defined and allocated bounds of an array,
  29 either with an out-of-range index
  30 or an out-of-bounds pointer.
  31 There is one exception:
  32 you may compute
  33 (but not access, or ``dereference'')
  34 a pointer to the imaginary element
  35 which sits one past the end of an array.
  36 Therefore,
  37 a common idiom for accessing an array using a pointer looks
  38 like
  39 <pre>   int a[10];
  40         int *ip;
  41 <br>
  42 <br>
  43         for (ip = &amp;a[0]; ip &lt; &amp;a[10]; ip++)
  44                 ...
  45 </pre>or
  46 <pre>   int a[10];
  47         int *endp = &amp;a[10];
  48         int *ip;
  49 <br>
  50 <br>
  51         for (ip = a; ip &lt; endp; ip++)
  52                 ...
  53 </pre>The element <TT>a[10]</TT> does not exist
  54 (the allocated elements run from <TT>[0]</TT> to <TT>[9]</TT>),
  55 but we may compute the pointer <TT>&amp;a[10]</TT>,
  56 and use it in expressions like
  57 <TT>ip &lt; &amp;a[10]</TT>
  58 and
  59 <TT>endp = &amp;a[10]</TT>.
  60 </p><p>Deep sentence:
  61 <blockquote>Don't assume, however,
  62 that the size of a structure is the sum of the sizes of its members.
  63 </blockquote>If this isn't the sort of thing you'd be likely to assume,
  64 you don't have to remember the reason,
  65 which is mildly esoteric
  66 (having to do with memory alignment requirements).
  67 </p><hr>
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  76 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
  77 // <a href="copyright.html">Copyright</a> 1995, 1996
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