Reading Performance Data from a Log File

The following example reads data written to a log file in the Writing Performance Data to a Log File example. It uses the PdhCollectQueryData function to retrieve the data from the log file and the PdhGetFormattedCounterValue function to format the data for display.

#include <windows.h>
#include <stdio.h>
#include <pdh.h>
#include <pdhmsg.h>

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

CONST PWSTR COUNTER_PATH    = L"\\Processor(0)\\% Processor Time";

void DisplayCommandLineHelp(void)
{
    wprintf(L"The command line must contain a valid log file name.\n");
}

void wmain(int argc, WCHAR **argv)
{
    HQUERY hQuery = NULL;
    HCOUNTER hCounter = NULL;
    PDH_STATUS status = ERROR_SUCCESS;
    DWORD dwFormat = PDH_FMT_DOUBLE; 
    PDH_FMT_COUNTERVALUE ItemBuffer;

    if (argc != 2) 
    {
        DisplayCommandLineHelp();
        goto cleanup;
    }

    // Opens the log file to write performance data
    status = PdhOpenQuery(argv[1], 0, &hQuery);

    if (ERROR_SUCCESS != status)
    {
        wprintf(L"PdhOpenQuery failed with 0x%x\n", status);
        goto cleanup;
    }
   
    // Add the same counter used when writing the log file.
    status = PdhAddCounter(hQuery, COUNTER_PATH, 0, &hCounter);
   
    if (ERROR_SUCCESS != status)
    {
        wprintf(L"PdhAddCounter failed with 0x%x\n", status);
        goto cleanup;
    }

    // Read a performance data record.
    status = PdhCollectQueryData(hQuery);

    if (ERROR_SUCCESS != status)
    {
        wprintf(L"PdhCollectQueryData failed with 0x%x\n", status);
        goto cleanup;
    }

    while (ERROR_SUCCESS == status) 
    { 
        // Read the next record
        status = PdhCollectQueryData(hQuery);

        if (ERROR_SUCCESS == status)
        {
            // Format the performance data record.
            status = PdhGetFormattedCounterValue(hCounter,
                dwFormat,
                (LPDWORD)NULL,
                &ItemBuffer);

            if (ERROR_SUCCESS != status)
            {
                wprintf(L"PdhGetFormattedCounterValue failed with 0x%x.\n", status);
                goto cleanup;
            }

            wprintf(L"Formatted counter value = %.20g\n", ItemBuffer.doubleValue);
        }
        else
        {
            if (PDH_NO_MORE_DATA != status)
            {
                wprintf(L"PdhCollectQueryData failed with 0x%x\n", status);
            }
        }
    }

cleanup:

    // Close the query.
    if (hQuery)
        PdhCloseQuery(hQuery);
}