Hello Danial.
07 Apr 97 16:53, Danial Gibson wrote to All:
 DG> a program to chat between the computers. So I read the win32 sdk
 DG> and thought, gee, pipes look good. So I did that for two hours
 DG> wondering why it wouldn't work. Found out it's cause pipes are only in
 DG> nt, not 95.
I've been down that alley to :-(
 DG>         1. Why does it get it twice?
dont know!
 DG>         2. Will it _always_ get it twice?
I think so.
 DG>         3. If the answer to 2 is no, then how do I fix it?
After reading your message i made a small program to see if it was true  - 
and it was. Maybe it is a bug in the windows SDK, or maybe there is a reason 
for it - not really obvious to me though.
I dont know which compiler you're using. I'm using MS Visual C++ 4.0. If 
you're using the same compiler, it could be a problem with the compiler.
The short of the long is, that I  found a way to get by it. Not in a very 
elegant way, but it works: The basic idea is to only take every 2 messages 
from the mailslot, when you are reading it, using the MODULUS (%) function.
The next few lines of code shows the functions I'm using (do not get confused 
with the MFC syntax - the mailslot functions are pure API code using the 
Windows SDK).
Most of the code comes directly from the Visual C++ online help.
////////////////////// Start
BOOL CMailSlotDlg::Makeslot()
{
    LPSTR lpszSlotName = "\\\\.\\mailslot\\sample_mailslot";
    /* The mailslot handle "hSlot1" is declared globally. */
    m_hSlot1 = CreateMailslot(lpszSlotName,
        0,                         /* no maximum message size         */
        MAILSLOT_WAIT_FOREVER,     /* no time-out for read operations */
        (LPSECURITY_ATTRIBUTES) NULL); /* no security attributes      */
    if (m_hSlot1 == INVALID_HANDLE_VALUE) {
        ErrorHandler("CreateMailslot"); /* local error handler */
        return FALSE;
    }
    SetDlgItemText(IDC_STATUS, "CreateMailslot successful.");
    return TRUE;
}
void CMailSlotDlg::ErrorHandler(LPSTR msg)
{
MessageBox(msg);
}
BOOL CMailSlotDlg::Readslot()
{
    DWORD cbMessage, cMessage, cbRead;
    BOOL fResult;
    LPSTR lpszBuffer;
    CHAR achID[80];
        DWORD cAllMessages;
    cbMessage = cMessage = cbRead = 0;
    /* Mailslot handle "hSlot1" is declared globally. */
    fResult = GetMailslotInfo(m_hSlot1, /* mailslot handle         */
        (LPDWORD) NULL,               /* no maximum message size */
        &cbMessage,                   /* size of next message    */
        &cMessage,                    /* number of messages      */
        (LPDWORD) NULL);              /* no read time-out        */
    if (!fResult) {
        ErrorHandler("GetMailslotInfo");
        return FALSE;
    }
    if (cbMessage == MAILSLOT_NO_MESSAGE) {
        SetDlgItemText(IDC_STATUS, "No waiting messages.");
        return TRUE;
    }
    cAllMessages = cMessage;
    int counter = 0;
    while (cMessage != 0) {              /* retrieves each message  */
        counter ++;
        /* Create a message-number string. */
        wsprintf((LPSTR) achID,
            "\nMessage #%d of %d\n", (cAllMessages - (cMessage))/2 + 1,
            cAllMessages/2);
        /* Allocate memory for the message. */
        lpszBuffer = (LPSTR) GlobalAlloc(GPTR,
            lstrlen((LPSTR) achID) + cbMessage);
        lpszBuffer[0] = '\0';
        fResult = ReadFile(m_hSlot1,
            lpszBuffer,
            cbMessage,
            &cbRead,
            (LPOVERLAPPED) NULL);
        if (!fResult) {
            ErrorHandler("ReadFile");
            GlobalFree((HGLOBAL) lpszBuffer);
            return FALSE;
        }
        /* Concatenate the message and the message-number string. */
        lstrcat(lpszBuffer, (LPSTR) achID);
        /* Display the message. */
        if (counter %2 == 0)
            MessageBox(lpszBuffer, "Contents of Mailslot", MB_OK);
        GlobalFree((HGLOBAL) lpszBuffer);
        fResult = GetMailslotInfo(m_hSlot1, /* mailslot handle         */
            (LPDWORD) NULL,               /* no maximum message size */
            &cbMessage,                   /* size of next message    */
            &cMessage,                    /* number of messages      */
            (LPDWORD) NULL);              /* no read time-out        */
        if (!fResult) {
            ErrorHandler("GetMailslotInfo");
            return FALSE;
        }
    }
    return TRUE;
}
void CMailSlotDlg::OnCheckmail()
{
    // TODO: Add your control notification handler code here
    Readslot();
}
BOOL CMailSlotDlg::WriteMessage(LPSTR lpszMessage)
{
//LPSTR lpszMessage = "12_Bogstaver";
BOOL fResult;
HANDLE hFile;
DWORD cbWritten;
hFile = CreateFile("\\\\*\\mailslot\\sample_mailslot",
    GENERIC_WRITE,
    FILE_SHARE_READ, /* required to write to a mailslot */
    (LPSECURITY_ATTRIBUTES) NULL,
    OPEN_EXISTING,
    FILE_ATTRIBUTE_NORMAL,
    (HANDLE) NULL);
if (hFile == INVALID_HANDLE_VALUE) {
    ErrorHandler("Primary domain"); /* local error handler */
    return FALSE;
}
fResult = WriteFile(hFile,
    lpszMessage,
    (DWORD) lstrlen(lpszMessage) + 1, /* include terminat. null char. */
    &cbWritten,
    (LPOVERLAPPED) NULL);
if (!fResult) {
    ErrorHandler("WriteFile");
    return FALSE;
}
SetDlgItemText(IDC_STATUS, "WriteFile successful.");
fResult = CloseHandle(hFile);
if (!fResult) {
    ErrorHandler("CloseHandle");
    return FALSE;
}
SetDlgItemText(IDC_STATUS, "CloseHandle successful.");
return TRUE;
}
void CMailSlotDlg::OnSendmail()
{
    // TODO: Add your control notification handler code here
    GetDlgItemText(IDC_EDIT, m_NewMessage);
    WriteMessage(PCHAR(m_NewMessage));
}
////////////////////// End
Good luck!
Please tell me, if you find a more elegant way to solve the problem
Christian
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