LOCAL and GLOBAL

Variables in ScriptBasic for Java need not be declared. They are created automatically when the program execution sees a variable. When a variable is used in a subroutine, however it can be either a local or a global variable. The interpreter can not derive the intention of the programmer and for this reason there are two commands LOCAL and GLOBAL that can be used to declare variables.

Inside a subroutine all variables are local unless defined global.

A variable can be declared tio be global inside a subroutine or in the main program code. LOCAL and GLOBAL declarations can be used in subroutines only before the first executable command. In the main program you can use GLOBAL anywhere.

Lets have a look at the following program:

' Program demonstrating global
' and local variables

gVar1 = "global"
gVar2 = "global"
anyVar = "global"
arg = "global"

GLOBAL myLocalVar2

sub mySub(arg)

  LOCAL anyVar, myLocalVar
  GLOBAL gVar2

  anyVar = "local"
  arg = "local"
  gVar1 = "local"
  gVar2 = "local"
  myLocalVar1 = "local"
  myLocalVar2 = "local"

endsub


mySub "argument"

print "gVar1=",gVar1
print "\n"
print "gVar2=",gVar2
print "\n"
print "anyVal=",anyVar
print "\n"
print "arg=",arg
print "\n"
print "myLocalVar1=",myLocalVar1
print "\n"
print "myLocalVar2=",myLocalVar2
print "\n"

The output of the program is

gVar1=global
gVar2=local
anyVal=global
arg=global
myLocalVar1=undef
myLocalVar2=undef

Only the variable gVar2 was modified to hold the string "local" in the subroutine, because that is the only variable declared to be global. All other variables including the argument is local.

Practice

Treating all variables local unless declared global is a safe practice. This prevents a subroutine to accidentally overwrite the value of a global variable.

Even though it is not required to declare every variable, it is a good practice to declare variables either to be global and local. ScriptBasic for Java has an internal feature that makes it possible to programmatically configure the interpreter to alter the behavior above. It can be forced to treat any non declared variable global inside subroutines. Use ScriptBasic for Java only if you really have to because what you do is actually harm your BASIC programmers.

The other possible programmatic configuration is to treat any non declared variable an error. To make the interpreter usable this way the GLOBAL keyword can be used in the main program code and you can declare any local variable as LOCAL inside a subroutine.