VB2010 Express Net MidiOutOpen错误

问题描述

''当我注意到我愚蠢地使用ByVal lphMidiOut而不是ByRef时，以下问题已得到解决!!!!向所有人致歉.

``我对为什么该程序失败感到困惑

''The problem described below has now been solved when I noticed I had stupidly put ByVal lphMidiOut instead of ByRef !!!! Apologies to all.

''I am baffled as to why this program fails

Imports System.Runtime.InteropServices
Public Class Form1
    Declare Function midiOutOpen Lib "winmm.dll" Alias "midiOutOpen" _
        (ByVal lphMidiOut As Int32, ByVal uDeviceID As Int32, _
         ByVal dwCallback As Int32, ByVal dwInstance As Int32, _
         ByVal dwFlags As Int32) As Int32

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
                            Handles Me.Load
        Dim lpMO As Int32
        Dim rv As Int32 = midiOutOpen(lpMO, -1, 0, 0, 0)
        Debug.Print(CStr(rv))

        '''''  the above code returns error 11 (MMSYSERR_INVALPARAM) ?? '''''
        '''''           -1 is the uDeviceID for the MIDI_MAPPER         '''''
        '''''  It also fails for uDeviceID = 0 (my on-board sound card) '''''
    End Sub
End Class

为什么有人知道?

''Anyone got an idea as to why?

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