Variable declaration modifier specifying visibility throughout a module

Dim Shared ...
Redim Shared ...
Common Shared ...
Static Shared ...

Shared makes module-level variables visible inside Subs and Functions.
If Shared is not used on a module-level variable's declaration, the variable is only visible to the module-level code in that file (furthermore, only a variable declared with Dim without Shared modifier, and not inside a Namespace block, is stored on the stack).

NOTES (for Shared variables excluding Common variables):
  • Generally a Shared variable may only be initialized with a constant value (its starting value is set at the start of the program in the .data section before any code is run, and so it cannot depend on any variables or functions in it).
  • A first exception is a Shared variable of var-len string type, that never can be initialized, even with a constant string (because of its structure with a descriptor in the .data section, but to point to a dynamic memory block).
  • A second exception is a Shared variable of user-defined type having a constructor even implicit, that can be initialized with a non-constant value (because it's the constructor code, called when the program starts, which writes the "initial" values into the .data section).

'' Compile with -lang qb or fblite

'$lang: "qb"

Declare Sub MySub
Dim Shared x As Integer
Dim y As Integer

x = 10
y = 5


Sub MySub
    Print "x is "; x 'this will report 10 as it is shared
    Print "y is "; y 'this will not report 5 because it is not shared
End Sub

Differences from QB:
See also:
Back to Variable Declarations
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