Extern...End Extern
Statement block to allow calling of functions compiled for specific languages or platforms.
Extern { "C" | "C++" | "Windows" | "Windows-MS" } [ Lib "libname" ]
Extern blocks provide default calling conventions for procedures and mandate a certain name decoration.
Extern "C" blocks provide a default cdecl calling convention to procedures, and also preserve the case of all names declared within them. The same effect can be achieved without the EXTERN block by using cdecl together with an Alias string containing the exact procedure name.
Extern "C++" blocks are exactly like Extern "C" blocks but they also mangle the names declared within them in a way compatible to that of g++-4.x.
Extern "Windows" blocks provide a default stdcall calling convention to procedures, preserve the case of all names declared within them, and on the Windows platform, append an "@N" suffix to procedure names, where N is the total size in bytes of any procedure parameters. Similar to the Extern "C" block, the same effect can be achieved by using stdcall and Alias.
Extern "Windows-MS" blocks are exactly like Extern "Windows" blocks but do not append the "@N" suffix to procedure names on Windows.
Lib "libname" can be used to specify a library which will be linked in as if #Inclib "Libname" or -l libname had been used. Additionally, all procedure declarations inside the Extern block will use the specified Lib "libname" as if it was specified as part of their declarations (but it can still be overridden with an explicit Lib "libname").
Syntax
Extern { "C" | "C++" | "Windows" | "Windows-MS" } [ Lib "libname" ]
declarative statements
End ExternDescription
Extern blocks provide default calling conventions for procedures and mandate a certain name decoration.
Extern "C" blocks provide a default cdecl calling convention to procedures, and also preserve the case of all names declared within them. The same effect can be achieved without the EXTERN block by using cdecl together with an Alias string containing the exact procedure name.
Extern "C++" blocks are exactly like Extern "C" blocks but they also mangle the names declared within them in a way compatible to that of g++-4.x.
Extern "Windows" blocks provide a default stdcall calling convention to procedures, preserve the case of all names declared within them, and on the Windows platform, append an "@N" suffix to procedure names, where N is the total size in bytes of any procedure parameters. Similar to the Extern "C" block, the same effect can be achieved by using stdcall and Alias.
Extern "Windows-MS" blocks are exactly like Extern "Windows" blocks but do not append the "@N" suffix to procedure names on Windows.
Lib "libname" can be used to specify a library which will be linked in as if #Inclib "Libname" or -l libname had been used. Additionally, all procedure declarations inside the Extern block will use the specified Lib "libname" as if it was specified as part of their declarations (but it can still be overridden with an explicit Lib "libname").
Example
Extern "C"
'' This procedure uses the CDECL convention and is seen externally
'' as "SomeProcedure".
Declare Sub SomeProcedure ( ByVal As Integer )
End Extern
Extern "C++"
'' This procedure uses the CDECL convention and its name is mangled
'' compatible to that of g++-4.x.
Declare Function AnotherProcedure ( ByVal As Integer ) As Integer
End Extern
Extern "Windows"
'' This procedure uses the STDCALL convention and is seen externally
'' as "YetAnotherProcedure@4" on Windows, and
'' "YetAnotherProcedure" on Linux, *BSD and DOS.
Declare Function YetAnotherProcedure ( ByVal As Integer ) As Integer
End Extern
Extern "Windows-MS"
'' This procedure uses the STDCALL convention and is seen externally
'' as "YetAnotherProcedure".
Declare Function YetAnotherProcedure ( ByVal As Integer ) As Integer
End Extern
'' This procedure uses the CDECL convention and is seen externally
'' as "SomeProcedure".
Declare Sub SomeProcedure ( ByVal As Integer )
End Extern
Extern "C++"
'' This procedure uses the CDECL convention and its name is mangled
'' compatible to that of g++-4.x.
Declare Function AnotherProcedure ( ByVal As Integer ) As Integer
End Extern
Extern "Windows"
'' This procedure uses the STDCALL convention and is seen externally
'' as "YetAnotherProcedure@4" on Windows, and
'' "YetAnotherProcedure" on Linux, *BSD and DOS.
Declare Function YetAnotherProcedure ( ByVal As Integer ) As Integer
End Extern
Extern "Windows-MS"
'' This procedure uses the STDCALL convention and is seen externally
'' as "YetAnotherProcedure".
Declare Function YetAnotherProcedure ( ByVal As Integer ) As Integer
End Extern
Dialect Differences
- Extern blocks are only available in the -lang fb dialect.
Differences from QB
- New to FreeBASIC
Platform Differences
- On Linux, *BSD and DOS platforms, Extern "Windows" blocks never append a "@N" suffix to procedure names, and thus are equal to Extern "Windows-MS".
See also
