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   9 <title>section 6.2: Structures and Functions</title>
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  15 <H2>section 6.2: Structures and Functions</H2>
  16
  17 <p>In this section,
  18 we'll begin playing with structures
  19 more or less as if they were ordinary variables
  20 such as we've been using all along
  21 (which they more or less are).
  22 As we'll see,
  23 we can
  24 declare variables of structure type,
  25 declare functions which accept structures as parameters and return them,
  26 declare pointers to structures,
  27 take the address of a structure
  28 (creating a pointer-to-structure)
  29 with <TT>&amp;</TT>,
  30 and assign structures.
  31 </p><p>Notice that when we declare something as ``a structure type,''
  32 we always have to say <em>which</em> structure type,
  33 usually by using the struct tag.
  34 If we've set up a ``point'' structure as above,
  35 then to declare a variable of this type,
  36 we say
  37 <pre>   struct point thepoint;
  38 </pre>Both
  39 <pre>   struct thepoint;        /* WRONG */
  40 </pre>and
  41 <pre>   point thepoint;         /* WRONG */
  42 </pre>would be errors.
  43 </p><p>The above list of things the language lets us do with structures
  44 lets us keep them and move them around,
  45 but there isn't really anything defined by the language
  46 that we can <em>do</em> with structures.
  47 It's up to us to define any operations on structures,
  48 usually by writing functions.
  49 (The <TT>addpoint</TT> function on page 130 is a good example.
  50 It will make a bit more sense
  51 if you think of it as adding not isolated points,
  52 but rather vectors.
  53
  54 [We can't add Seattle plus Los Angeles,
  55 but we could add
  56 (two miles south, one mile east)
  57 plus
  58 (one mile east, two miles north).])
  59 </p><p>page 131
  60 </p><p>As an aside,
  61 how safe are the <TT>min()</TT> and <TT>max()</TT>
  62 macros defined at the top of page 131,
  63 with respect to the criteria
  64 discussed on pages 15 and 16
  65
  66 of the notes
  67 on section 4.11.2 (page 90 in the text)?
  68 </p><p>The precise meaning of the ``shorthand'' <TT>-&gt;</TT> operator
  69 is that <TT>sp-&gt;m</TT> is,
  70 by definition,
  71 equivalent
  72
  73 to <TT>(*sp).m</TT>,
  74 for any structure pointer <TT>sp</TT>
  75 and member <TT>m</TT> of the pointed-to structure.
  76 </p><hr>
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  85 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
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