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<h4 class="subsection">A.1.7 Accessing Global Variables in Oct-Files</h4>

<p>Global variables allow variables in the global scope to be
accessed.  Global variables can easily be accessed with oct-files using
the support functions <code>get_global_value</code> and
<code>set_global_value</code>.  <code>get_global_value</code> takes two arguments,
the first is a string representing the variable name to obtain.  The
second argument is a boolean argument specifying what to do in the case
that no global variable of the desired name is found.  An example of the
use of these two functions is

<pre class="example"><pre class="verbatim">     #include &lt;octave/oct.h>
     
     DEFUN_DLD (globaldemo, args, , "Global demo.")
     {
       int nargin = args.length ();
       octave_value retval;
     
       if (nargin != 1)
         print_usage ();
       else
         {
           std::string s = args(0).string_value ();
           if (! error_state)
             {
               octave_value tmp = get_global_value (s, true);
               if (tmp.is_defined ())
                 retval = tmp;
               else
                 retval = "Global variable not found";
     
               set_global_value ("a", 42.0);
             }
         }
       return retval;
     }
</pre></pre>
   <p>An example of its use is

<pre class="example">     global a b
     b = 10;
     globaldemo ("b")
     &rArr; 10
     globaldemo ("c")
     &rArr; "Global variable not found"
     num2str (a)
     &rArr; 42
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