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<a name="Global-Variables"></a>
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<a name="Global-Variables-1"></a>
<h3 class="section">7.1 Global Variables</h3>
<a name="index-global-variables"></a>
<a name="index-global-statement"></a>
<a name="index-variables_002c-global"></a>

<p>A variable that has been declared <em>global</em> may be accessed from
within a function body without having to pass it as a formal parameter.
</p>
<p>A variable may be declared global using a <code>global</code> declaration
statement.  The following statements are all global declarations.
</p>
<div class="example">
<pre class="example">global a
global a b
global c = 2
global d = 3 e f = 5
</pre></div>

<p>A global variable may only be initialized once in a <code>global</code>
statement.  For example, after executing the following code
</p>
<div class="example">
<pre class="example">global gvar = 1
global gvar = 2
</pre></div>

<p>the value of the global variable <code>gvar</code> is 1, not 2.  Issuing a
&lsquo;<samp>clear gvar</samp>&rsquo; command does not change the above behavior, but
&lsquo;<samp>clear all</samp>&rsquo; does.
</p>
<p>It is necessary declare a variable as global within a function body in
order to access it.  For example,
</p>
<div class="example">
<pre class="example">global x
function f ()
  x = 1;
endfunction
f ()
</pre></div>

<p>does <em>not</em> set the value of the global variable <code>x</code> to 1.  In
order to change the value of the global variable <code>x</code>, you must also
declare it to be global within the function body, like this
</p>
<div class="example">
<pre class="example">function f ()
  global x;
  x = 1;
endfunction
</pre></div>

<p>Passing a global variable in a function parameter list will
make a local copy and not modify the global value.  For example, given
the function
</p>
<div class="example">
<pre class="example">function f (x)
  x = 0
endfunction
</pre></div>

<p>and the definition of <code>x</code> as a global variable at the top level,
</p>
<div class="example">
<pre class="example">global x = 13
</pre></div>

<p>the expression
</p>
<div class="example">
<pre class="example">f (x)
</pre></div>

<p>will display the value of <code>x</code> from inside the function as 0,
but the value of <code>x</code> at the top level remains unchanged, because
the function works with a <em>copy</em> of its argument.
</p>
<a name="XREFisglobal"></a><dl>
<dt><a name="index-isglobal"></a>: <em></em> <strong>isglobal</strong> <em>(<var>name</var>)</em></dt>
<dd><p>Return true if <var>name</var> is a globally visible variable.
</p>
<p>For example:
</p>
<div class="example">
<pre class="example">global x
isglobal (&quot;x&quot;)
   &rArr; 1
</pre></div>

<p><strong>See also:</strong> <a href="Variables.html#XREFisvarname">isvarname</a>, <a href="Status-of-Variables.html#XREFexist">exist</a>.
</p></dd></dl>


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