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GNU Octave Manual Version 3
by John W. Eaton, David Bateman, Søren Hauberg
Paperback (6"x9"), 568 pages
ISBN 095461206X
RRP £24.95 ($39.95)

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7.1 Global Variables

A variable that has been declared global may be accessed from within a function body without having to pass it as a formal parameter.

A variable may be declared global using a global declaration statement. The following statements are all global declarations.

global a
global a b
global c = 2
global d = 3 e f = 5

A global variable may only be initialized once in a global statement. For example, after executing the following code

global gvar = 1
global gvar = 2

the value of the global variable gvar is 1, not 2. Issuing a ‘clear gvar’ command does not change the above behavior, but ‘clear all’ does.

It is necessary declare a variable as global within a function body in order to access it. For example,

global x
function f ()
  x = 1;
f ()

does not set the value of the global variable x to 1. In order to change the value of the global variable x, you must also declare it to be global within the function body, like this

function f ()
  global x;
  x = 1;

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

function f (x)
  x = 0

and the definition of x as a global variable at the top level,

global x = 13

the expression

f (x)

will display the value of x from inside the function as 0, but the value of x at the top level remains unchanged, because the function works with a copy of its argument.

Built-in Function: isglobal (name)
Return 1 if name is globally visible. Otherwise, return 0. For example,

global x
isglobal ("x")
     => 1
ISBN 095461206XGNU Octave Manual Version 3See the print edition