<html lang="en"> <head> <title>Global Variables - Untitled</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="Untitled"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Variables.html#Variables" title="Variables"> <link rel="next" href="Persistent-Variables.html#Persistent-Variables" title="Persistent Variables"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="Global-Variables"></a> <p> Next: <a rel="next" accesskey="n" href="Persistent-Variables.html#Persistent-Variables">Persistent Variables</a>, Up: <a rel="up" accesskey="u" href="Variables.html#Variables">Variables</a> <hr> </div> <h3 class="section">7.1 Global Variables</h3> <p><a name="index-global-variables-423"></a><a name="index-g_t_0040code_007bglobal_007d-statement-424"></a><a name="index-variables_002c-global-425"></a> A variable that has been declared <dfn>global</dfn> may be accessed from within a function body without having to pass it as a formal parameter. <p>A variable may be declared global using a <code>global</code> declaration statement. The following statements are all global declarations. <pre class="example"> global a global a b global c = 2 global d = 3 e f = 5 </pre> <p>A global variable may only be initialized once in a <code>global</code> statement. For example, after executing the following code <pre class="example"> global gvar = 1 global gvar = 2 </pre> <p class="noindent">the value of the global variable <code>gvar</code> is 1, not 2. Issuing a ‘<samp><span class="samp">clear gvar</span></samp>’ command does not change the above behavior, but ‘<samp><span class="samp">clear all</span></samp>’ does. <p>It is necessary declare a variable as global within a function body in order to access it. For example, <pre class="example"> global x function f () x = 1; endfunction f () </pre> <p class="noindent">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 <pre class="example"> function f () global x; x = 1; endfunction </pre> <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 <pre class="example"> function f (x) x = 0 endfunction </pre> <p class="noindent">and the definition of <code>x</code> as a global variable at the top level, <pre class="example"> global x = 13 </pre> <p class="noindent">the expression <pre class="example"> f (x) </pre> <p class="noindent">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. <!-- variables.cc --> <p><a name="doc_002disglobal"></a> <div class="defun"> — Built-in Function: <b>isglobal</b> (<var>name</var>)<var><a name="index-isglobal-426"></a></var><br> <blockquote><p>Return 1 if <var>name</var> is globally visible. Otherwise, return 0. For example, <pre class="example"> global x isglobal ("x") ⇒ 1 </pre> </blockquote></div> </body></html>