[RESOLVED] Cant get mciGetErrorString API to work

Using: Visual Studio 2008 SP1
Language: VB.NET

I am using the API 'mciSendString' to record audio to a WAV file, this works fine. As i want to monitor 'mciSendString' API for errors i am using the 'mciGetErrorString' API. I cannot get the 'mciGetErrorString' API to work as it keeps failing with errors when run.

I have googled the code many times and modified it to use different types of buffers to stores its values and it still fails to work or displays a different type of error message. Please can you inform me what i may be doing wrong or give a working code example.

Below is one example of my code:

Displays the message "Arithmetic operation resulted in an overflow" when run :(

Code:

---

   

    Dim errorcode As Long

    Declare Function mciSendString Lib "winmm.dll" Alias "mciSendStringA" (ByVal lpstrCommand As String, ByVal lpstrReturnString As String, ByVal uReturnLength As Long, ByVal hwndCallback As Long) As Long

    Declare Auto Function mciGetErrorString Lib "winmm.dll" (ByVal fdwError As Integer, ByVal lpszErrorText As String, ByVal cchErrorText As Integer) As Boolean

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        errorcode = mciSendString("open new type waveaudio alias RecWavFile", 0&, 0, 0)
        errorcode = mciSendString("set RecWavFile channels 2", 0, 0, 0) ' Stereo Or Mono Sound
        errorcode = mciSendString("set RecWavFile samplespersec " & CBKhz.SelectedItem, 0, 0, 0) ' Khz Rate
        errorcode = mciSendString("set RecWavFile bitspersample " & CBBit.SelectedItem, 0, 0, 0) ' Sound Sample Rate (Bits)
        errorcode = mciSendString("record RecWavFile", 0&, 0, 0)
        ' Start recording in the highest quality format for .WAV PCM Audio
        ' Recording will only work if the sound card supports the chosen KHZ / BIT rate

        If errorcode <> 0 Then
            MessageBox.Show(GetMCIErrorString(errorcode))
        End If

    End Sub

Private Function GetMCIErrorString(ByVal errorcode As Long) As String
        'create a buffer
        GetMCIErrorString = Space$(128)
        'retrieve the error string
        mciGetErrorString(errorcode, GetMCIErrorString, Len(GetMCIErrorString))
        ''strip off the trailing spaces
        GetMCIErrorString = Trim$(GetMCIErrorString)
 End Function

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Preface: I'm not a .Net guy
Which line does the error occur in?
I see you declared LONG parameter types & return value in mciSendString, shouldn't they be Integer?
And the mciGetErrorString API declaration should return Integer not Boolean, correct?

Edited: Another declaration definition

Code:

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'In VB6
Private Declare Function mciGetErrorString Lib "winmm.dll" Alias "mciGetErrorStringA" (ByVal ErrorNumber As Long, ByVal ReturnBuffer As String, ByVal ReturnBufferSize As Long) As Long
Private Declare Function mciGetErrorStringW Lib "winmm" (ByVal dwError As Long, ByVal lpstrBuffer As Long, ByVal uLength As Long) As Long

' Get the error that just occured (if one did occur)

Private Function GetLastErr_MCI(Optional ByVal ErrorNumber As Long, _
                                Optional ByVal LastAPICalled As String = "last", _
                                Optional ByRef Return_ErrNum As Long, _
                                Optional ByRef Return_ErrDesc As String, _
                                Optional ByVal ShowErrors As Boolean = False) As Boolean

Dim intErrorNumber As Integer

' Clear return variables

    Return_ErrNum = 0
    Return_ErrDesc = ""

    ' If no error occured, exit
    If ErrorNumber = 0 Then
        Exit Function
    Else
        intErrorNumber = LOWORD(ErrorNumber)
    End If

    ' Assign initial values
    GetLastErr_MCI = True
    Return_ErrNum = CLng(intErrorNumber)
    If LastAPICalled = "" Then LastAPICalled = "last"

    ' Get the error description based on the error number
    Return_ErrDesc = String(260, Chr(0))
    If m_bUseUnicode Then
        If mciGetErrorStringW(Return_ErrNum, StrPtr(Return_ErrDesc), 260) <> 0 Then
            Return_ErrDesc = Left(Return_ErrDesc, InStr(Return_ErrDesc, Chr(0)) - 1)
        Else
            Return_ErrDesc = "Unknown Error"
        End If
    Else
        If mciGetErrorString(Return_ErrNum, Return_ErrDesc, 260) <> 0 Then
            Return_ErrDesc = Left(Return_ErrDesc, InStr(Return_ErrDesc, Chr(0)) - 1)
        Else
            Return_ErrDesc = "Unknown Error"
        End If
    End If

    ' If specified to show an error message, do so
    If ShowErrors = True Then
        MsgBox "The following error occured while calling the " & LastAPICalled _
              & " MCI API:" & Chr(13) & Chr(13) & _
              "Error Number = " & Return_ErrNum & Chr(13) & _
              "Error Description = " & Return_ErrDesc, vbOKOnly + vbExclamation, "  MCI ERROR"
    End If

End Function

' Function that extracts the "Low Order" (lower 16bits) of a 32bit number

Private Function LOWORD(ByVal dwValue As Long) As Integer

    LOWORD = Val("&H" & Right("0000" & Hex(dwValue), 4))

End Function

' Function that extracts the "High Order" (upper 16bits) of a 32bit number

Private Function HIWORD(ByVal dwValue As Long) As Integer

    HIWORD = Val("&H" & Left(Right("00000000" & Hex(dwValue), 8), 4))

End Function

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These seems to be catching error and working in VB10 / .Net4 for me.

Code:

---

Public Class Form1
    Private Declare Function mciSendString Lib "winmm.dll" Alias "mciSendStringA" (ByVal lpstrCommand As String, ByVal lpstrReturnString As String, ByVal uReturnLength As Integer, ByVal hwndCallback As Integer) As Integer
    Private Declare Function mciGetErrorString Lib "winmm.dll" Alias "mciGetErrorStringA" (ByVal dwError As Integer, ByVal lpstrBuffer As String, ByVal uLength As Integer) As Integer
    Dim ErrCode As Integer

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim RetStr As String = Space(1024)
        ErrCode = mciSendString("open new type waveaudio alias RecWavFile", RetStr, 1024, 0)
        If ErrCode = 0 Then
            ErrCode = mciSendString("set RecWavFile channels 2", RetStr, 1024, 0) ' Stereo Or Mono Sound
            If ErrCode = 0 Then
                ErrCode = mciSendString("set RecWavFile samplespersec 44100", RetStr, 1024, 0) ' Khz Rate
                If ErrCode = 0 Then ' Make it error...... bitspersample = 6 <<< (should be 8 or 16?)
                    ErrCode = mciSendString("set RecWavFile bitspersample 6", RetStr, 1024, 0) ' Sound Sample Rate (Bits)
                    If ErrCode = 0 Then
                        ErrCode = mciSendString("record RecWavFile", RetStr, 1024, 0)
                    End If
                End If
            End If
        End If

        If ErrCode <> 0 Then MessageBox.Show(GetMCIErrorString(ErrCode))

    End Sub

    Private Function GetMCIErrorString(ByVal ErrorCode As Integer) As String
        'create a buffer
        GetMCIErrorString = Space(1024)
        'retrieve the error string
        mciGetErrorString(ErrorCode, GetMCIErrorString, Len(GetMCIErrorString))
        'strip off the trailing spaces
        GetMCIErrorString = Trim(GetMCIErrorString)
    End Function

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        ' // stop  and save to file //
        Dim RetStr As String = Space(1024) 'Will show error here if path/folder doesn't exist
        ErrCode = mciSendString("save RecWavFile D:\TEST\RecWavFile.wav", RetStr, 1024, 0)
        If ErrCode <> 0 Then MessageBox.Show(GetMCIErrorString(ErrCode))
        ErrCode = mciSendString("close RecWavFile", RetStr, 1024, 0)
        If ErrCode <> 0 Then MessageBox.Show(GetMCIErrorString(ErrCode))
    End Sub
End Class

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Thanks everyone for their assistance with this :)

@Edgemeal

Thanks for your code example, works a treat :) . Think my code was almost there and i had obviously declared the API incorrectly based on your working code.