COMMON

• Source: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgCommon
• Last revised: 2021-10-05

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Variable declaration and scope modifier

Syntax

` Common [Shared] symbolname[()] [AS DataType] [, ...]

`

Description

Declares a variable which is shared between code modules, including those to be compiled as static and dynamic libraries (DLLs).

A matching Common statement must appear in all other code modules using the variable.

Common variables cannot be initialized.

Common arrays are always variable-length, and must be defined with an empty parameter list (), and its dimensions set in a later Dim or Redim statement.

Common variables cannot be instances of a user-defined type having a constructor or a destructor even implicit.

The Shared optional parameter makes the variable global so that it can be used inside subs and functions, as well as at module level.

Examples

start GeSHi

'' common1.bas

Declare Sub initme()

Common Shared foo() As Double

ReDim foo(0 To 2)

initme()

Print foo(0), foo(1), foo(2)

end GeSHi

start GeSHi

'' common2.bas

Common Shared foo() As Double

Sub initme()
  foo(0) = 4*Atn(1)
  foo(1) = foo(0)/3
  foo(2) = foo(1)*2
End Sub

end GeSHi

After compiling the two files like:

fbc common1.bas common2.bas

running common1 produces the output:

 3.141592653589793           1.047197551196598           2.094395102393195

Platform Differences

• Windows does not support Common with a dynamic library (compiled with -dll or -dylib).

Differences from QB

• The arrays will be always variable-length.
• blockname is not needed and must be removed because the order of declaration no longer matters, only the symbol names.
• Common does not allow to keep the values of certain variables when chaining programs with Chain.

See also

• Dim
• Erase
• Extern
• Lbound
• Redim
• Preserve
• Shared
• Static
• Ubound
• Var

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