winlog.cpp

// heavily modified version of https://copyprogramming.com/howto/using-mailslots#reading-from-a-mailslot

#include <iostream>
#include <Windows.h>

#define csMe "WinlogMonitor"
#define csMailslotName "WinLog"

int main()
{
    HANDLE hSlot = CreateMailslotW(TEXT("\\\\.\\mailslot\\" csMailslotName), -1, MAILSLOT_WAIT_FOREVER, NULL);
    if (hSlot == INVALID_HANDLE_VALUE) {
        printf("<CreateMailslot failed with %d>\n", GetLastError());
        return 1;
    }

    HANDLE hEvent = CreateEvent(NULL, FALSE, FALSE, TEXT(csMe));
    if (!hEvent) {
        printf("<CreateEvent failed with %d>\n", GetLastError());
        CloseHandle(hSlot);
        return 1;
    }

    OVERLAPPED hOverlapped = {};
    hOverlapped.Offset = 0;
    hOverlapped.OffsetHigh = 0;
    hOverlapped.hEvent = hEvent;

    printf("<Waiting for messages in mailslot %s>\n\n", csMailslotName);

    DWORD cbNextSize = 0;
    for (;;) {  // keep looking for messages (so it will use a bit of cpu)
        if (!GetMailslotInfo(hSlot, NULL, &cbNextSize, NULL, NULL)) {
            printf("<GetMailslotInfo failed with %d>\n", GetLastError());
            continue;
        }
        if (cbNextSize == MAILSLOT_NO_MESSAGE)
            continue;

        std::string lpszBuffer(cbNextSize + 1, '\0');
        if (!ReadFile(hSlot, &lpszBuffer[0], cbNextSize, NULL, &hOverlapped)) {
            printf("<ReadFile failed with %d>\n", GetLastError());
            continue;
        }
        std::cout << lpszBuffer;
    }

    CloseHandle(hSlot);
    CloseHandle(hEvent);
    return 0;
}