vb6代码报错：Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer Private Const WM_APPCOMMAND As Integer = &H319 Private Const APPCOMMAND_VOLUME_UP As Integer = &HA Private Const APPCOMMAND_VOLUME_DOWN As Integer = &H9 Private Const APPCOMMAND_VOLUME_MUTE As Integer = &H8 Private Sub IncreaseVolume() SendMessage(Me.Handle, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_UP * &H10000) End Sub Private Sub DecreaseVolume() SendMessage(Me.Handle, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_DOWN * &H10000) End Sub Private Sub MuteVolume() SendMessage(Me.Handle, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_MUTE * &H10000) End Sub

这段代码是使用 VB6 调用 Windows API 函数来控制系统音量的，但是在 64 位 Windows 上可能会出现问题。如果你在 64 位 Windows 上运行这段代码，可能会收到“找不到指定的DLL”的错误消息。
为了解决这个问题，你需要使用 PtrSafe 关键字来声明指针类型，以及使用 LongPtr 类型来代替 Long 类型。
修改后的代码如下：
Private Declare PtrSafe Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As LongPtr, ByVal wMsg As Long, ByVal wParam As LongPtr, ByVal lParam As LongPtr) As LongPtr
Private Const WM_APPCOMMAND As Long = &H319
Private Const APPCOMMAND_VOLUME_UP As Long = &HA
Private Const APPCOMMAND_VOLUME_DOWN As Long = &H9
Private Const APPCOMMAND_VOLUME_MUTE As Long = &H8
Private Sub IncreaseVolume()
SendMessage Me.hWnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_UP * &H10000
End Sub
Private Sub DecreaseVolume()
SendMessage Me.hWnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_DOWN * &H10000
End Sub
Private Sub MuteVolume()
SendMessage Me.hWnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_MUTE * &H10000
End Sub
注意，在使用 PtrSafe 关键字时，你需要在代码文件的开头添加 Option Explicit 和 #If Win64 Then ... #Else ... #End If 的指令。完整的代码如下：
Option Explicit
#If Win64 Then
Private Declare PtrSafe Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As LongPtr, ByVal wMsg As Long, ByVal wParam As LongPtr, ByVal lParam As LongPtr) As LongPtr
#Else
Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
#End If
Private Const WM_APPCOMMAND As Long = &H319
Private Const APPCOMMAND_VOLUME_UP As Long = &HA
Private Const APPCOMMAND_VOLUME_DOWN As Long = &H9
Private Const APPCOMMAND_VOLUME_MUTE As Long = &H8
Private Sub IncreaseVolume()
SendMessage Me.hWnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_UP * &H10000
End Sub
Private Sub DecreaseVolume()
SendMessage Me.hWnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_DOWN * &H10000
End Sub
Private Sub MuteVolume()
SendMessage Me.hWnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_MUTE * &H10000
End Sub