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GNU Octave

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 b = 2 global c = 3, d, e = 5

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; endfunction 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; endfunction

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 endfunction

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 Variable: warn_comma_in_global_decl

If the value of warn_comma_in_global_decl is nonzero, a warning is issued for statements like

global a = 1, b

which makes the variables a and b global and assigns the value 1 to the variable a, because in this context, the comma is not interpreted as a statement separator.

The default value of warn_comma_in_global_decl is nonzero.

initialize_global_variables:

if the value of initialize_global_variables is nonzero, global variables are initialized to the value of the built-in variable default_global_variable_value.

the default value of initialize_global_variables is zero.

default_global_variable_value:

if initialize_global_variables is nonzero, the value of default_glbaol_variable_value is used as the initial value of global variables that are not explicitly initialized. for example,

initialize_global_variables = 1; default_global_variable_value = 13; global foo; foo => 13

the variable default_global_variable_value is initially undefined.

Built-in Function: is_global (name)

Return 1 if name is globally visible. Otherwise, return 0. For example,

global x is_global ("x") => 1