VB动态调用DLL

在编程时，有时无法确定某个函数是否会在使用者的Windows中存在，这种情况一般是由于Win9X和WinNT的区别造成的。用BCB可以使用动态加载的方法解决这个问题，但是按照这个思路用VB做的时候遇到了一点麻烦，那就是GetProcAddress返回的是一个指向函数的指针，VB里不知道怎么通过函数指针调用函数。不过，我们可以通过一些变通的方法来达到我们的目的，请看程序例。程序是用VB.NET写的，如果你用VB，请自己改一下函数声明和类型定义
Module Module1

Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Integer

Declare Function FreeLibrary Lib "kernel32" (ByVal hLibModule As Integer) As Integer

Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Integer, ByVal lpProcName As String) As Integer

'要使用动态调用的函数，也要在这里声明，VB.NET是可以声明不存在的函数的。

'例如我们需要调用DllGetVersion这个函数，但我们其实不知道这个函数是否存在。

'为了达到效果，我们故意声明了一个不存在的函数MyDllGetVersion。

'先定义需要的类型。

Structure DLLVERSIONINFO

Public cbSize As Integer

Public dwMajor As Integer

Public dwMinor As Integer

Public dwBuildNumber As Integer

Public dwPlatformId As Integer

Public dwFlag As Integer

Public ddUllVer As Long

End Structure

Declare Function DllGetVersion Lib "COMCTL32" (ByRef pdvi As DLLVERSIONINFO) As Integer

Declare Function MyDllGetVersion Lib "COMCTL32" (ByRef pdvi As DLLVERSIONINFO) As Integer

Sub Main()

Dim hMod As Integer

Dim Ret As Integer

Dim pfDllVersion As Integer

Dim tDVI As DLLVERSIONINFO

hMod = LoadLibrary("comctl32.dll")

If hMod <> 0 Then

pfDllVersion = GetProcAddress(hMod, "DllGetVersion")

If (pfDllVersion <> 0) Then

tDVI.cbSize = Len(tDVI)

Ret = DllGetVersion(tDVI) '注意，我们无法将pfDllVersion转换为需要的函数类型指针，但由于已经声明，可以直接使用。

If (Ret = 0) Then

Console.WriteLine("DLL Version:" & tDVI.dwMajor & "." & tDVI.dwMinor & "." & tDVI.dwBuildNumber)

Else

Console.WriteLine("Function DllGetVersion failed.")

End If

Else

Console.WriteLine("DllGetVersion not exist.")

End If

pfDllVersion = GetProcAddress(hMod, "MyDllGetVersion")

If (pfDllVersion <> 0) Then

tDVI.cbSize = Len(tDVI)

Ret = MyDllGetVersion(tDVI)

If (Ret = 0) Then

Console.WriteLine("My DLL Version:" & tDVI.dwMajor & "." & tDVI.dwMinor & "." & tDVI.dwBuildNumber)

Else

Console.WriteLine("Function MyDllGetVersion failed.")

End If

Else

Console.WriteLine("MyDllGetVersion not exist.")

End If

FreeLibrary(hMod)

End If

End Sub

End Module