Mailslot application does not receive messages 
Author Message
 Mailslot application does not receive messages

After several news posting, and reading, I have assembled a couple of
functions to create a mailslot, and send and receive messages.
It seems that all is working, except ReadFile() function in
cmdReceive_click().
This function allways returns 0, after GetMailSlotInfo() indicates that
there are messages to retrieve.

Anyone can help with it ?

Option Explicit

Private fhSlot As Long

Private Declare Function CloseHandle Lib "kernel32" _
    (ByVal hHandle As Long) As Long

Private Declare Function ReadFile Lib "kernel32" (ByVal hFile As Long, _
    lpBuffer As Any, nNumberOfBytesToRead As Long, _
    lpNumberOfBytesRead As Long, ByVal lpOverlapped As Long) As Long

Private Declare Function WriteFile Lib "kernel32" (ByVal hFileName As Long,
_
    ByVal lpBuff As Any, _
    ByVal nNrBytesToWrite As Long, lpNrOfBytesWritten As Long, _
    ByVal lpOverlapped As Long) As Long

Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" _
    (ByVal lpFileName As String, ByVal dwAccess As Long, _
    ByVal dwShare As Long, ByVal lpSecurityAttrib As Long, _
    ByVal dwCreationDisp As Long, ByVal dwAttributes As Long, _
    ByVal hTemplateFile As Long) As Long

Private Declare Function GetMailslotInfo Lib "kernel32" (ByVal hMailslot As
Long, _
    ByVal lpMaxMessageSize As Long, lpNextSize As Long, _
    lpMessageCount As Long, ByVal lpReadTimeout As Long) As Long

Private Declare Function CreateMailslot Lib "kernel32" Alias
"CreateMailslotA" _
    (ByVal lpName As String, ByVal nMaxMessageSize As Long, _
    ByVal lReadTimeout As Long, ByVal lpSecurityAttributes As Long) As Long

Private Const OPEN_EXISTING = 3
Private Const GENERIC_READ = &H80000000
Private Const GENERIC_WRITE = &H40000000
Private Const GENERIC_EXECUTE = &H20000000
Private Const GENERIC_ALL = &H10000000
Private Const INVALID_HANDLE_VALUE = -1
Private Const FILE_SHARE_READ = &H1
Private Const FILE_SHARE_WRITE = &H2
Private Const FILE_ATTRIBUTE_NORMAL = &H80
Private Const MAILSLOT_WAIT_FOREVER = (-1)

Private Sub cmdCreate_Click()
   Dim mslotname As String

   mslotname$ = "\\.\mailslot\tst"
   fhSlot& = CreateMailslot(mslotname$, 0, MAILSLOT_WAIT_FOREVER, 0)
   If fhSlot& = INVALID_HANDLE_VALUE Then MsgBox "Error creating mailslot"
End Sub

Private Sub cmdReceive_Click()
   Dim stat As Long, bytesread As Long
   Dim mslotname As String, msg As String
   Dim sizemsg As Long, nummsgs As Long

   sizemsg& = 0
   nummsgs& = 0
   bytesread& = 0

   stat& = GetMailslotInfo(fhSlot&, 0, sizemsg&, nummsgs&, 0)
   If stat& = 0 Then MsgBox "Error in mailslotinfo"
   If nummsgs& = 0 Then MsgBox "No messages present"

   Do While sizemsg& <> 0
      msg$ = Chr$(0) & Space$(sizemsg&) & Space$(80)
      stat& = ReadFile(fhSlot&, msg$, sizemsg&, bytesread&, 0)
      If stat& = 0 Then
         MsgBox "Error reading mslot"
         Exit Do
      End If

      MsgBox "THE MESSAGE IS : ->" & msg$ & "<-"

      stat& = GetMailslotInfo(fhSlot&, 0, sizemsg&, nummsgs&, 0)
      If stat& = 0 Then MsgBox "Error in mailslotinfo"
      If nummsgs& = 0 Then MsgBox "No more messages"
   Loop
End Sub

Private Sub cmdSend_Click()
   Dim stat As Long
   Dim msg As String
   Dim byteswritten As Long
   Dim mslotname As String
   Dim hFile As Long

   hFile& = CreateFile("\\*\mailslot\tst", GENERIC_WRITE, _
                      FILE_SHARE_READ, 0, OPEN_EXISTING, _
                      FILE_ATTRIBUTE_NORMAL, 0)
   If hFile& = INVALID_HANDLE_VALUE Then MsgBox "Error creating file"

   msg$ = "HELLO WORLD!"
   stat& = WriteFile(hFile&, msg$, Len(msg$) + 1, byteswritten, 0)
   If stat& = 0 Then MsgBox "Error writing file"

   stat& = CloseHandle(hFile&)
   If stat& = 0 Then MsgBox ("Error closing file")
End Sub

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
   Dim stat&

   stat& = CloseHandle(fhSlot&)
End Sub



Sat, 24 Mar 2001 03:00:00 GMT  
 
 [ 2 post ] 

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