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I'm having trouble with the CreateMailslot function.

Posted on 1997-05-16
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Last Modified: 2006-11-17
I've been trying to use the CreateMailslot function from kernel32 and I keep getting an INVALID_HANDLE_VALUE returned by the call.

I've tried the following C++ code in a DLL and it works :-

#include <iostream.h>
#include <windows.h>

long create_slot (void);

HANDLE hM_slot;


BOOL WINAPI DllEntryPoint (HINSTANCE hDll, DWORD dwReason, LPVOID Reserved)

{
      switch (dwReason)
      {
            case DLL_PROCESS_ATTACH:
            {
                  break;
            }
            case DLL_PROCESS_DETACH:
            {
                  break;
            }
      }
      return TRUE;
}

long create_slot (void)
{
      hM_slot=CreateMailslot("\\\\.\\mailslot\\test_mail_slot",0,MAILSLOT_WAIT_FOREVER,(LPSECURITY_ATTRIBUTES) NULL);
      return hM_slot;
}

In VB 4.0 I tried the following :-

Type SECURITY_ATTRIBUTES
        nLength As Long
        lpSecurityDescriptor As Long
        bInheritHandle As Boolean
End Type

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

Global slot_num As Long
Global Const MAILSLOT_WAIT_FOREVER = (-1)


Private Sub Command1_Click()
    Dim security As SECURITY_ATTRIBUTES
    slot_num = CreateMailslot("\\.\mailslot\mailslottest", 0, MAILSLOT_WAIT_FOREVER, security)
    MsgBox slot_num
End Sub

It doesn't work! So I tried this :-

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

Global slot_num As Long
Global Const MAILSLOT_WAIT_FOREVER = (-1)


Private Sub Command1_Click()
    slot_num = CreateMailslot("\\.\mailslot\mailslottest", 0, MAILSLOT_WAIT_FOREVER, Null)
    MsgBox slot_num
End Sub

Still doesn't work!
0
Comment
Question by:mikekr
2 Comments
 
LVL 5

Accepted Solution

by:
y96andha earned 200 total points
ID: 1426348
It has to do with the specification of the C value NULL. Use this code:

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 slot_num As Long
Private Const MAILSLOT_WAIT_FOREVER = (-1)

Private Sub Command1_Click()
slot_num = CreateMailslot("\\.\mailslot\mailslottest", 0, MAILSLOT_WAIT_FOREVER, 0)
MsgBox slot_num
End Sub



0
 

Author Comment

by:mikekr
ID: 1426349
Thanks... It worked!!!!
0

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