Externkeyword

Declares a variable, array or object having external linkage

Syntax

Extern [ Import ] symbolname[ (subscripts) ] [ Alias "aliasname" ] As DataType [, ...]

Parameters

Description

Declares symbolname as an external name, meaning it is global to external modules including those to be compiled as static and dynamic libraries (DLLs).
Extern only declares variables, arrays and objects, and does not define them (different from Common or Dim). It also has the effect of making symbolname a shared name, meaning it is visible within procedures (see Shared). A symbolname declared as external name can be (re)defined (using Dim or Redim) only in a single external module.

If Alias is used, aliasname will be used as the external name rather than symbolname, and its case will be preserved.

Extern was added in order to support the C libraries.

If Import is used, the name will be added to the dynamic library import list so its address can be fixed at run-time.

Remarks

Platform Differences

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

Dialect Differences

• Not available in the -lang qb dialect.
  
  

Differences from QB

• New to FreeBASIC
  
  

See also

• Extern...End Extern
  
• Common
  
• Dim
  
• Shared
  
• Alias (Name)
  
• Alias (Modifier)
  
  

Example

'' extern1.bas



Extern Foo Alias "foo" As Integer



Sub SetFoo

    foo = 1234

End Sub

'' extern2.bas



Declare Sub SetFoo



Extern Foo Alias "foo" As Integer



Dim foo As Integer = 0



SetFoo



Print Foo

Output:

 1234

Reference

• Documented in KeyPgExtern.html