lang/C/the.ansi.c.programming.language/notes.accompany.ansi.c/sx7i.html

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   9 <title>section 4.9: Initialization</title>
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  15 <H2>section 4.9: Initialization</H2>
  16
  17 page 85
  18 <p>These are <em>some</em> of the rules on initialization;
  19 we'll learn a few more later
  20 as we learn about a few more data types.
  21 </p><p>If you don't feel like memorizing the rules for default initialization,
  22 just go ahead and explicitly initialize everything you care about.
  23 </p><p>Earlier we said that C is quite general in its treatment of expressions:
  24 anywhere you can use an expression,
  25 you can use any expression.
  26 Here's an exception to that rule:
  27 in an initialization of an external or static variable
  28 (strictly speaking, any variable of static duration;
  29 generally speaking, any global variable
  30 or local <TT>static</TT> variable),
  31 the initializer must be a constant expression,
  32 with value determinable at compile time,
  33 without calling any functions.
  34 (This rule is easy to understand:
  35 since these initializations
  36 happen
  37 conceptually at compile time,
  38 before the program starts running,
  39 there's no way for a function call--that is,
  40 some run-time action--to be involved.)
  41 </p><p>page 86
  42 </p><p>It probably won't concern you right away,
  43 but it turns out that there's another exception
  44 about the allowable expressions in initializers:
  45 in the brace-enclosed list of initializers for an array,
  46 all of the expressions must be constant expressions
  47 (even for local arrays).
  48
  49 </p><p>There is an error in some printings:
  50 if there are fewer explicit initializers than required for an array,
  51 the others will be initialized to zero,
  52 for external, static, <em>and</em> automatic (local) arrays.
  53 (When an automatic array has no initializers at all,
  54 then it contains garbage,
  55 just as simple automatic variables do.)
  56 </p><p>If the initialization
  57 <pre>   char pattern[] = "ould";
  58 </pre>makes sense to you, you're fine.
  59 But if the statement that
  60 <pre>   char pattern[] = "ould";
  61 </pre>is equivalent to
  62 <pre>   char pattern[] = { 'o', 'u', 'l', 'd', '\0' };
  63 </pre>bothers you at all,
  64 study it until it makes sense.
  65 Also, note that a character array which seems to contain
  66 (for example)
  67 four characters
  68 actually contains five, because of the terminating <TT>'\0'</TT>.
  69 </p><hr>
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  78 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
  79 // <a href="copyright.html">Copyright</a> 1995, 1996
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