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
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
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; 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
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.