How to use DLL in my VB program ?

BarryTang
BarryTang used Ask the Experts™
on
For the present, I would like to write a VB program that
read the content of a midi ( .mid ) file by using the
reading function in a external DLL.

Since I have not familiar to write program that call
functions in external DLL file, would someone give me some guildline/reference code to initialize this program.

You can refer to the DLL that located in the following
web site:
http://www.borg.com/~jglatt/progs/software.htm
The DLL is midifile.dll and the function I need to use should be MidiReadFile()

Thank you for your help


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Hi,

For what you have, do something like this:
At the start of your VB program, put the following lines:

Private Declare Function readMidiFile Lib "MidiFile" Alias "MidiReadFile"  (midiFileName miFileName as Any)

and then you would have can use the function like:
readMidiFile("c:\your_file_name.mid")

Now - actually looking at the documentation for that, it appears that you might actually need
a file handle (as opposed to just a character string), so you may need to do something like:
open "testmidi.mid" for input as #1
but for this method, I am not 100% sure how that would be done...

however, let me know if the above works for you

Author

Commented:
Hello, cool12399 :

Thanks for reply !

I try to write few VB lines according to what you suggest
in a form as follows :

Private Declare Function MidiReadFile Lib "MidiFile" (ByVal tmid As String) As Long

Private Sub Command1_Click()
  Open "test.mid" For Input As #1
  x = MidiReadFile("test.mid")
End Sub

Actually I cannot run these code, the program and the VB development will be terminated when it try to execute the line :
  x = MidiReadFile("test.mid")

I don't know if there is something wrong ( or missing
some procedure ). Would you please help me to find out
the problem.

Thank you very much

Barry



In VB either multimedia file or data file the storage and retrival of file attributes procedure is same.You can use standard file handling controls to do what you want.If your particular about Using DLL for this you can try with the standard file handling DLLs.I am furnishing an example below.cut it and modify to your needs.
'Create a form with a command button (command1), a list box (list1)
'and four text boxes (text1, text2, text3 and text4).
'Type in the first textbox a startingpath like c:\
'and in the second textbox you put a pattern like *.* or *.txt

Private Declare Function FindFirstFile Lib "kernel32" Alias "FindFirstFileA" (ByVal lpFileName As String, lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare Function FindNextFile Lib "kernel32" Alias "FindNextFileA" (ByVal hFindFile As Long, lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare Function GetFileAttributes Lib "kernel32" Alias "GetFileAttributesA" (ByVal lpFileName As String) As Long
Private Declare Function FindClose Lib "kernel32" (ByVal hFindFile As Long) As Long

Const MAX_PATH = 260
Const MAXDWORD = &HFFFF
Const INVALID_HANDLE_VALUE = -1
Const FILE_ATTRIBUTE_ARCHIVE = &H20
Const FILE_ATTRIBUTE_DIRECTORY = &H10
Const FILE_ATTRIBUTE_HIDDEN = &H2
Const FILE_ATTRIBUTE_NORMAL = &H80
Const FILE_ATTRIBUTE_READONLY = &H1
Const FILE_ATTRIBUTE_SYSTEM = &H4
Const FILE_ATTRIBUTE_TEMPORARY = &H100

Private Type FILETIME
    dwLowDateTime As Long
    dwHighDateTime As Long
End Type

Private Type WIN32_FIND_DATA
    dwFileAttributes As Long
    ftCreationTime As FILETIME
    ftLastAccessTime As FILETIME
    ftLastWriteTime As FILETIME
    nFileSizeHigh As Long
    nFileSizeLow As Long
    dwReserved0 As Long
    dwReserved1 As Long
    cFileName As String * MAX_PATH
    cAlternate As String * 14
End Type
Function StripNulls(OriginalStr As String) As String
    If (InStr(OriginalStr, Chr(0)) > 0) Then
        OriginalStr = Left(OriginalStr, InStr(OriginalStr, Chr(0)) - 1)
    End If
    StripNulls = OriginalStr
End Function

Function FindFilesAPI(path As String, SearchStr As String, FileCount As Integer, DirCount As Integer)
    'KPD-Team 1999
    'E-Mail: KPDTeam@Allapi.net
    'URL: http://www.allapi.net/

    Dim FileName As String ' Walking filename variable...
    Dim DirName As String ' SubDirectory Name
    Dim dirNames() As String ' Buffer for directory name entries
    Dim nDir As Integer ' Number of directories in this path
    Dim i As Integer ' For-loop counter...
    Dim hSearch As Long ' Search Handle
    Dim WFD As WIN32_FIND_DATA
    Dim Cont As Integer
    If Right(path, 1) <> "\" Then path = path & "\"
    ' Search for subdirectories.
    nDir = 0
    ReDim dirNames(nDir)
    Cont = True
    hSearch = FindFirstFile(path & "*", WFD)
    If hSearch <> INVALID_HANDLE_VALUE Then
        Do While Cont
        DirName = StripNulls(WFD.cFileName)
        ' Ignore the current and encompassing directories.
        If (DirName <> ".") And (DirName <> "..") Then
            ' Check for directory with bitwise comparison.
            If GetFileAttributes(path & DirName) And FILE_ATTRIBUTE_DIRECTORY Then
                dirNames(nDir) = DirName
                DirCount = DirCount + 1
                nDir = nDir + 1
                ReDim Preserve dirNames(nDir)
            End If
        End If
        Cont = FindNextFile(hSearch, WFD) 'Get next subdirectory.
        Loop
        Cont = FindClose(hSearch)
    End If
    ' Walk through this directory and sum file sizes.
    hSearch = FindFirstFile(path & SearchStr, WFD)
    Cont = True
    If hSearch <> INVALID_HANDLE_VALUE Then
        While Cont
            FileName = StripNulls(WFD.cFileName)
            If (FileName <> ".") And (FileName <> "..") Then
                FindFilesAPI = FindFilesAPI + (WFD.nFileSizeHigh * MAXDWORD) + WFD.nFileSizeLow
                FileCount = FileCount + 1
                List1.AddItem path & FileName
            End If
            Cont = FindNextFile(hSearch, WFD) ' Get next file
        Wend
        Cont = FindClose(hSearch)
    End If
    ' If there are sub-directories...
    If nDir > 0 Then
        ' Recursively walk into them...
        For i = 0 To nDir - 1
            FindFilesAPI = FindFilesAPI + FindFilesAPI(path & dirNames(i) & "\", SearchStr, FileCount, DirCount)
        Next i
    End If
End Function
Sub Command1_Click()
    Dim SearchPath As String, FindStr As String
    Dim FileSize As Long
    Dim NumFiles As Integer, NumDirs As Integer
    Screen.MousePointer = vbHourglass
    List1.Clear
    SearchPath = Text1.Text
    FindStr = Text2.Text
    FileSize = FindFilesAPI(SearchPath, FindStr, NumFiles, NumDirs)
    Text3.Text = NumFiles & " Files found in " & NumDirs + 1 & " Directories"
    Text4.Text = "Size of files found under " & SearchPath & " = " & Format(FileSize, "#,###,###,##0") & " Bytes"
    Screen.MousePointer = vbDefault
End Sub
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BarryTang,
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Thank you.
Author of the Year 2009

Commented:
Hi BarryTang,
It appears that you have forgotten this question. I will ask Community Support to close it unless you finalize it within 7 days. I will ask a Community Support Moderator to:

    Accept cool12399's comment(s) as an answer.

BarryTang, if you think your question was not answered at all or if you need help, just post a new comment here; Community Support will help you.  DO NOT accept this comment as an answer.

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