Import
External linkage attribute for public data located in DLL's
Is used only (with the Extern keyword) in external modules to access global variables from 32-bit and 64-bit Windows DLLs: the variable names will be added to the dynamic library import list so that their addresses can be fixed at run-time.
This is due to the level of indirection on any such access: an implicit pointer dereference.
The declaration must match the DLL's C data type. A C int is 32 bits on both Windows targets, so use FreeBASIC Long. FreeBASIC Integer is native-sized and is 64 bits on Win64.
The import library and DLL must match the application's target architecture. Win32 and Win64 use different import-address symbol prefixes, which the compiler supplies automatically.
Syntax
Description
Is used only (with the Extern keyword) in external modules to access global variables from 32-bit and 64-bit Windows DLLs: the variable names will be added to the dynamic library import list so that their addresses can be fixed at run-time.
This is due to the level of indirection on any such access: an implicit pointer dereference.
The declaration must match the DLL's C data type. A C int is 32 bits on both Windows targets, so use FreeBASIC Long. FreeBASIC Integer is native-sized and is 64 bits on Win64.
The import library and DLL must match the application's target architecture. Win32 and Win64 use different import-address symbol prefixes, which the compiler supplies automatically.
Example
/*
Project: FreeBASIC manual examples
----------------------------------
File: examples/manual/module/mydll.c
Purpose:
Provide the C DLL used by the manual's IMPORT example.
Responsibilities:
- Export one Integer Data symbol from a Windows DLL
This file intentionally does Not contain:
- executable startup code
- FreeBASIC declarations For importing the symbol
See also:
https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgImport
*/
/* mydll.c :
compile With
gcc -Shared -Wl,--strip-all -Wl,--Out-implib,libmydll.dll.a -o mydll.dll mydll.c
*/
__declspec( dllexport ) Int MyDll_Data = 0x1234;
/* End of examples/manual/module/mydll.c */
Project: FreeBASIC manual examples
----------------------------------
File: examples/manual/module/mydll.c
Purpose:
Provide the C DLL used by the manual's IMPORT example.
Responsibilities:
- Export one Integer Data symbol from a Windows DLL
This file intentionally does Not contain:
- executable startup code
- FreeBASIC declarations For importing the symbol
See also:
https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgImport
*/
/* mydll.c :
compile With
gcc -Shared -Wl,--strip-all -Wl,--Out-implib,libmydll.dll.a -o mydll.dll mydll.c
*/
__declspec( dllexport ) Int MyDll_Data = 0x1234;
/* End of examples/manual/module/mydll.c */
'' examples/manual/module/import.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'IMPORT'
'' Purpose: Read a C DLL's exported 32-bit integer.
'' Responsibilities: DLL import linkage and matching the C data width.
'' This example contains no DLL implementation or runtime loading code.
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgImport
'' --------
/' import.bas :
Compile with
fbc import.bas
'/
#inclib "mydll"
'' C int remains 32 bits on both Win32 and Win64.
Extern Import MyDll_Data Alias "MyDll_Data" As Long
Print "&h" + Hex( MyDll_Data )
' Output:
' &h1234
'' end of import.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'IMPORT'
'' Purpose: Read a C DLL's exported 32-bit integer.
'' Responsibilities: DLL import linkage and matching the C data width.
'' This example contains no DLL implementation or runtime loading code.
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgImport
'' --------
/' import.bas :
Compile with
fbc import.bas
'/
#inclib "mydll"
'' C int remains 32 bits on both Win32 and Win64.
Extern Import MyDll_Data Alias "MyDll_Data" As Long
Print "&h" + Hex( MyDll_Data )
' Output:
' &h1234
'' end of import.bas
Dialect Differences
- Not available in the -lang qb dialect unless referenced with the alias __Import.
Differences from QB
- New to FreeBASIC
See also