将事件保存到日志文件

若要将通道中的事件保存到日志文件，请调用 EvtClearLog 或 EvtExportLog 函数。 EvtClearLog 函数将事件复制到日志文件，并从通道中删除这些事件。 EvtExportLog 函数还会将事件复制到日志文件，但不会将其从通道中删除。 若要清除频道，用户必须具有“读取”和“清除”权限。

可以从创建的日志文件中查询事件;但是，若要呈现事件，必须在计算机上注册提供程序。 若要在计算机上未注册提供程序时呈现日志文件中的事件，必须调用 EvtArchiveExportedLog，该日志从提供程序复制资源并将其添加到日志文件中。 然后，可以将日志文件复制到任何计算机，并成功查询和呈现其事件。

除了使用 EvtExportLog 从通道复制事件外，还可以使用它将事件从一个日志文件重新记录到另一个日志文件。 如果使用结构化 XML 查询，则还可以使用它来合并来自多个通道的事件，但不能使用它来合并来自多个日志文件的事件。

以下示例演示如何将事件从通道复制到日志文件。 然后，该示例将新创建的日志文件中的特定事件重新记录到新的日志文件中。

#include <windows.h>
#include <stdio.h>
#include <winevt.h>

#pragma comment(lib, "wevtapi.lib")

#define ARRAY_SIZE 10

DWORD DumpEvents(LPCWSTR pwsLogFile);
DWORD PrintResults(EVT_HANDLE hResults);
DWORD PrintEvent(EVT_HANDLE hEvent);

void main(void)
{
    DWORD status = ERROR_SUCCESS;
    LPWSTR pPath = L"<path to channel goes here>";
    LPWSTR pQuery = NULL;
    LPWSTR pTargetLogFile = L".\\log.evtx";

    // Export all the events in the specified channel to the target log file.
    if (!EvtExportLog(NULL, pPath, pQuery, pTargetLogFile, EvtExportLogChannelPath))
    {
        wprintf(L"EvtExportLog failed for initial export with %lu.\n", GetLastError());
        goto cleanup;
    }

    // Dump the events from the log file.
    wprintf(L"Events from %s log file\n\n", pTargetLogFile);
    DumpEvents(pTargetLogFile);

    // Create a new log file that will contain all events from the specified 
    // log file where the event ID is 2.
    pPath =  L".\\log.evtx";
    pQuery = L"Event/System[EventID=2]";
    pTargetLogFile = L".\\log2.evtx";

    // Export all events from the specified log file that have an ID of 2 and
    // write them to a new log file.
    if (!EvtExportLog(NULL, pPath, pQuery, pTargetLogFile, EvtExportLogFilePath))
    {
        wprintf(L"EvtExportLog failed for relog with %lu.\n", GetLastError());
        goto cleanup;
    }

    // Dump the events from the log file.
    wprintf(L"\n\n\nEvents from %s log file\n\n", pTargetLogFile);
    DumpEvents(pTargetLogFile);

cleanup:

    return;
}


// Dump all the events from the log file.
DWORD DumpEvents(LPCWSTR pwsPath)
{
    EVT_HANDLE hResults = NULL;
    DWORD status = ERROR_SUCCESS;

    hResults = EvtQuery(NULL, pwsPath, NULL, EvtQueryFilePath);
    if (NULL == hResults)
    {
        wprintf(L"EvtQuery failed with %lu.\n", status = GetLastError());
        goto cleanup;
    }

    status = PrintResults(hResults);

cleanup:

    if (hResults)
        EvtClose(hResults);

    return status;
}


// Enumerate all the events in the result set. 
DWORD PrintResults(EVT_HANDLE hResults)
{
    DWORD status = ERROR_SUCCESS;
    EVT_HANDLE hEvents[ARRAY_SIZE];
    DWORD dwReturned = 0;

    while (true)
    {
        // Get a block of events from the result set.
        if (!EvtNext(hResults, ARRAY_SIZE, hEvents, INFINITE, 0, &dwReturned))
        {
            if (ERROR_NO_MORE_ITEMS != (status = GetLastError()))
            {
                wprintf(L"EvtNext failed with %lu\n", status);
            }

            goto cleanup;
        }

        // For each event, call the PrintEvent function which renders the
        // event for display. PrintEvent is shown in RenderingEvents.
        for (DWORD i = 0; i < dwReturned; i++)
        {
            if (ERROR_SUCCESS == (status = PrintEvent(hEvents[i])))
            {
                EvtClose(hEvents[i]);
                hEvents[i] = NULL;
            }
            else
            {
                goto cleanup;
            }
        }
    }

cleanup:

    // Executed only if there was an error.
    for (DWORD i = 0; i < dwReturned; i++)
    {
        if (NULL != hEvents[i])
            EvtClose(hEvents[i]);
    }

    return status;
}


// Print the event as an XML string.
DWORD PrintEvent(EVT_HANDLE hEvent)
{
    DWORD status = ERROR_SUCCESS;
    DWORD dwBufferSize = 0;
    DWORD dwBufferUsed = 0;
    DWORD dwPropertyCount = 0;
    LPWSTR pRenderedContent = NULL;

    // The EvtRenderEventXml flag tells EvtRender to render the event as an XML string.
    if (!EvtRender(NULL, hEvent, EvtRenderEventXml, dwBufferSize, pRenderedContent, &dwBufferUsed, &dwPropertyCount))
    {
        if (ERROR_INSUFFICIENT_BUFFER == (status = GetLastError()))
        {
            dwBufferSize = dwBufferUsed;
            pRenderedContent = (LPWSTR)malloc(dwBufferSize);
            if (pRenderedContent)
            {
                EvtRender(NULL, hEvent, EvtRenderEventXml, dwBufferSize, pRenderedContent, &dwBufferUsed, &dwPropertyCount);
            }
            else
            {
                wprintf(L"malloc failed\n");
                status = ERROR_OUTOFMEMORY;
                goto cleanup;
            }
        }

        if (ERROR_SUCCESS != (status = GetLastError()))
        {
            wprintf(L"EvtRender failed with %d\n", GetLastError());
            goto cleanup;
        }
    }

    wprintf(L"\n\n%s", pRenderedContent);

cleanup:

    if (pRenderedContent)
        free(pRenderedContent);

    return status;
}

以下示例演示如何使用结构化 XML 查询合并来自多个通道的事件。 该示例替换了上一个示例中的 main 过程。

void main(void)
{
    DWORD status = ERROR_SUCCESS;
    LPWSTR pTargetLogFile = L".\\log.evtx";
    LPWSTR pQuery = L"<QueryList>"
                    L"  <Query Id='0'>"
                    L"    <Select Path='<path to channel goes here>'>*</Select>"
                    L"  </Query>"
                    L"  <Query Id='1'>"
                    L"    <Select Path='<path to channel goes here>'>*</Select>"
                    L"  </Query>"
                    L"</QueryList>";

    if (!EvtExportLog(NULL, NULL, pQuery, pTargetLogFile, EvtExportLogChannelPath)) 
    {
        wprintf(L"EvtExportLog failed with %lu.\n", GetLastError());
        goto cleanup;
    }

    wprintf(L"Events from %s log file\n\n", pTargetLogFile);
    DumpEvents(pTargetLogFile);

cleanup:

    return;
}