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   9 <title>15.4: Pointers to Structures</title>
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  15 <H2>15.4: Pointers to Structures</H2>
  16
  17 <p>[This section corresponds to K&amp;R Sec. 6.4]
  18 </p><p>Pointers in C are general; we can have pointers to any type.
  19 It turns out that pointers to structures are particularly useful.
  20 </p><p>We declare pointers to structures
  21 the same way we declare any other pointers:
  22 by preceding the variable name with an asterisk in the declaration.
  23 We could declare two pointers to <TT>struct complex</TT>
  24 with
  25 <pre>
  26         struct complex *p1, *p2;
  27 </pre>
  28 And, as before,
  29 we could set these pointers to point to actual variables of type complex:
  30 <pre>
  31         p1 = &amp;c2;
  32         p2 = &amp;c3;
  33 </pre>
  34 Then,
  35 <pre>
  36         *p1 = *p2
  37 </pre>
  38 would copy the structure pointed to by <TT>p2</TT>
  39 to the structure pointed to by <TT>p1</TT>
  40 (i.e. <TT>c3</TT> to <TT>c2</TT>),
  41 and
  42 <pre>
  43         p1 = p2
  44 </pre>
  45 would set <TT>p1</TT> to point wherever <TT>p2</TT> points.
  46 (None of this is new,
  47 these are the obvious analogs of how all
  48
  49 pointer assignments work.)
  50 If we wanted to access the member of a pointed-to structure,
  51 it would be a tiny bit messy--first
  52 we'd have to use <TT>*</TT> to get the structure pointed to,
  53 then <TT>.</TT> to access the desired member.
  54 Furthermore,
  55 since <TT>.</TT> has higher precedence than <TT>*</TT>,
  56 we'd have to use parentheses:
  57 <pre>
  58         (*p1).real
  59 </pre>
  60 (Without the parentheses,
  61 i.e. if we wrote simply <TT>*p1.real</TT>,
  62 we'd be taking the structure <TT>p1</TT>,
  63 selecting its member named <TT>real</TT>,
  64 and accessing the value that <TT>p1.real</TT> points to,
  65 which would be doubly nonfunctional,
  66 since the <TT>real</TT> member is in our ongoing example not a pointer,
  67 and <TT>p1</TT> is not a structure
  68 but rather a pointer to a structure,
  69 so the <TT>.</TT> operator won't work on it.)
  70 </p><p>Since pointers to structures are common,
  71 and the parentheses in the example above are a nuisance,
  72 there's another structure selection operator
  73 which works on pointers to structures.
  74 If <TT>p</TT> is a pointer to a structure
  75 and <TT>m</TT> is a member of that structure,
  76 then
  77 <pre>
  78         p-&gt;m
  79 </pre>
  80 selects that member of the pointed-to structure.
  81 The expression <TT>p-&gt;m</TT> is therefore exactly equivalent to
  82 <pre>
  83         (*p).m
  84 </pre>
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