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Howto
check whether a function can be called on a machine,
without calling it first
If we can
retrieve the procedure address of the function, the
function exists and can be called. But how do we
retrieve this address? This code shows it to you:
Declare Function
LoadLibrary Lib "kernel32" Alias "LoadLibraryA"
(ByVal lpLibFileName As String) As Long
Declare Function FreeLibrary Lib "kernel32"
(ByVal hLibModule As Long) As Long
Declare Function GetProcAddress Lib
"kernel32" (ByVal hModule As Long, ByVal
lpProcName As String) As Long
Function FunctionExists(sLibrary As String, sFunction
As String) As Boolean
Dim hLib As Long, hProc As Long
hLib = LoadLibrary(sLibrary)
If hLib = 0 Then
MsgBox "Unable to load the library!"
Exit Function
End If
hProc = GetProcAddress(hLib, sFunction)
If hProc = 0 Then
MsgBox "Unable to find the '" + sFunction +
"' entry point in the library '" + sLibrary
+ "'!"
Exit Function
End If
FreeLibrary hLib
FunctionExists = True
End Function
Here are
some examples:
MsgBox
FunctionExists("kernel32", "RtlMoveMemory")
'Should return True
MsgBox FunctionExists("kern32", "RtlMoveMemory")
'kern32 doesn't exist => the function should return
False
MsgBox FunctionExists("kernel32", "RtlMoveMyMemory")
'RtlMoveMyMemory doesn't exist => the function
should return False
Note:
always check with the function's alias.
For example, if you try to check whether the
GetWindowText-function is available on that computer,
call the FunctionExists-function
with the parameters "user32" and "GetWindowTextA",
not "GetWindowText".
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