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| 22 | <title>File-Scope Variables (GNU C Language Manual)</title>
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| 58 | <span id="File_002dScope-Variables"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Static-Local-Variables.html" accesskey="n" rel="next">Static Local Variables</a>, Previous: <a href="Local-Variables.html" accesskey="p" rel="prev">Local Variables</a>, Up: <a href="Variables.html" accesskey="u" rel="up">Variables</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
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| 61 | </div>
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| 62 | <hr>
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| 63 | <span id="File_002dScope-Variables-1"></span><h3 class="section">20.6 File-Scope Variables</h3>
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| 64 | <span id="index-file_002dscope-variables"></span>
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| 65 | <span id="index-global-variables"></span>
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| 66 | <span id="index-variables_002c-file_002dscope"></span>
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| 67 | <span id="index-variables_002c-global"></span>
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| 68 |
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| 69 | <p>A variable declaration at the top level in a file (not inside a
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| 70 | function definition) declares a <em>file-scope variable</em>. Loading a
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| 71 | program allocates the storage for all the file-scope variables in it,
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| 72 | and initializes them too.
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| 73 | </p>
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| 74 | <p>Each file-scope variable is either <em>static</em> (limited to one
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| 75 | compilation module) or <em>global</em> (shared with all compilation
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| 76 | modules in the program). To make the variable static, write the
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| 77 | keyword <code>static</code> at the start of the declaration. Omitting
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| 78 | <code>static</code> makes the variable global.
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| 79 | </p>
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| 80 | <p>The initial value for a file-scope variable can’t depend on the
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| 81 | contents of storage, and can’t call any functions.
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| 82 | </p>
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| 83 | <div class="example">
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| 84 | <pre class="example">int foo = 5; /* <span class="roman">Valid.</span> */
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| 85 | int bar = foo; /* <span class="roman">Invalid!</span> */
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| 86 | int bar = sin (1.0); /* <span class="roman">Invalid!</span> */
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| 87 | </pre></div>
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| 88 |
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| 89 | <p>But it can use the address of another file-scope variable:
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| 90 | </p>
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| 91 | <div class="example">
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| 92 | <pre class="example">int foo;
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| 93 | int *bar = &foo; /* <span class="roman">Valid.</span> */
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| 94 | int arr[5];
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| 95 | int *bar3 = &arr[3]; /* <span class="roman">Valid.</span> */
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| 96 | int *bar4 = arr + 4; /* <span class="roman">Valid.</span> */
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| 97 | </pre></div>
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| 98 |
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| 99 | <p>It is valid for a module to have multiple declarations for a
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| 100 | file-scope variable, as long as they are all global or all static, but
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| 101 | at most one declaration can specify an initial value for it.
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| 102 | </p>
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| 103 |
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