Visual Basic Programming Code Examples

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Determine if an API exists (can be called) from a machine



Determine if an API exists (can be called) from a machine

The following code checks to see if an API can be called from a machine:

Option Explicit

Private Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long
Private Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Long, ByVal lpProcName As String) As Long
Private Declare Function FreeLibrary Lib "kernel32" (ByVal hLibModule As Long) As Long

'Purpose   :    Determines if a specific API is available on a machine.
'Inputs    :    sFunctionName               The name of the function within the library eg. "FindWindowA".
'               sDllName                    The name of the DLL eg. "user32".
'Outputs   :    Returns True if the API is available on this machine.
'Notes     :    Do NOT use an alias name for sFunctionName, you must use the original API name.
'               eg. use "FindWindowA" rather then the commonly used alias "FindWindow".

Function APIAvailable(ByVal sFunctionName As String, ByVal sDllName As String) As Boolean
    Dim lHandle As Long, lAddr As Long

    On Error Resume Next
    'Load the library
    lHandle = LoadLibrary(sDllName)
    If lHandle <> 0 Then
        'Get the address to the function name
        APIAvailable = CBool(GetProcAddress(lHandle, sFunctionName))
        'Release the resource
        FreeLibrary lHandle
    Else
        APIAvailable = False
    End If
    On Error Goto 0

End Function

'Demonstration routine
Sub Test()
    If APIAvailable("FindWindowA", "user32") Then
        MsgBox "API call FindWindowA is available..."
    Else
        MsgBox "API call FindWindowA is NOT available..."
    End If
End Sub