Command DLLFUNCTION Foundation
Creates a user-level function which executes a function of an external DLL. The command is deprecated. Use the EXTERN command instead.
DLLFUNCTION <FunctionName>( [[@]<Parameters,...>] ) ;
USING CDECL | OSAPI | STDCALL | SYSTEM ;
FROM <DllName>
Key word | Description |
---|---|
CDECL | C calling convention |
OSAPI *) | Calling convention for the operating system API |
STDCALL | Calling convention for the Windows 32bit API |
SYSTEM | Calling convention for the OS/2 API |
|
The DLLFUNCTION command is used to call functions from 32bit DLL files which are linked dynamically. It allows the utilization of functions within an Xbase++ application which are not known by the linker at the time when the EXE file is created. This includes operating system APIs as well as functions contained in DLLs of 3rd party producers.
The command creates an Xbase++ wrapper function which has the same name as the function contained in the DLL file <DllName>. Therefore, a DLL function can be called on the Xbase++ language level using a symbolic identifier.
When the Xbase++ function is called in a program, it first loads the DLL and then executes the DLL function of the same name. If parameters are declared, the Xbase++ function passes the received arguments to the DLL function. All parameters that are declared with a preceeding reference operator (@) are passed by reference to the DLL function. When the DLL function finishes, the DLL is unloaded and the Xbase++ function returns the return value of the DLL function.
// The example uses Windows API functions to read the network name of
// a work station from Windows' Registry database. Reading an entry
// from the Registry is done with the user defined function
// QueryRegistry()
#include "Dll.ch"
// #defines for the Registry database must comply
// with the Windows SDK
#define HKEY_CLASSES_ROOT 2147483648
#define HKEY_CURRENT_USER 2147483649
#define HKEY_LOCAL_MACHINE 2147483650
#define HKEY_USERS 2147483651
#define KEY_QUERY_VALUE 1
#define KEY_SET_VALUE 2
#define KEY_CREATE_SUB_KEY 4
#define KEY_ENUMERATE_SUB_KEYS 8
#define KEY_NOTIFY 16
#define KEY_CREATE_LINK 32
PROCEDURE Main
? "NETNAME - determines the network name of a work station"
? NetName()
RETURN
// Returns network name of a work station
FUNCTION NetName()
#ifdef __WIN32__
LOCAL cKey, cEntry
cKey := "System\CurrentControlSet\" + ;
"Control\ComputerName\ComputerName"
cEntry := "ComputerName"
RETURN QueryRegistry( HKEY_LOCAL_MACHINE, cKey, cEntry )
#endif
#ifdef __OS2__
RETURN GetEnv( "HOSTNAME" )
#endif
// Declare Xbase++ wrapper functions for each API-call
DLLFUNCTION RegOpenKeyExA( nHkeyClass, cKeyName, ;
nReserved , nAccess , @nKeyHandle) ;
USING STDCALL ;
FROM ADVAPI32.DLL
DLLFUNCTION RegQueryValueExA( nKeyHandle, cEntry , nReserved, ;
@nType , @cName , @nSize ) ;
USING STDCALL ;
FROM ADVAPI32.DLL
DLLFUNCTION RegCloseKey( nKeyHandle ) ;
USING STDCALL ;
FROM ADVAPI32.DLL
// Read values from the Windows Registry database
FUNCTION QueryRegistry( nHKEY, cKey, cEntry )
LOCAL cName := "" // All parameters passed to
LOCAL nSize := 0 // API functions must have
LOCAL nHandle:= 0 // a value not equal to NIL
LOCAL nType := 0
LOCAL nRet
// Open Registry key
nRet := RegOpenKeyExA( nHKEY, cKey, ;
0, KEY_QUERY_VALUE, @nHandle )
IF nRet <> 0 // Error
RETURN cName // ** RETURN **
ENDIF
// Determine size and type
// of the entry
RegQueryValueExA( nHandle, cEntry, 0, ;
@nType , @cName, @nSize )
IF nSize > 0 // Prepare empty string. It is
cName := Space( nSize-1 ) // passed by reference to the
// API and contains the result
// afterwards
RegQueryValueExA( nHandle, cEntry, 0, ;
nType , @cName, @nSize )
ENDIF
RegCloseKey( nHandle ) // Close Registry key
RETURN cName
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