Which operations update last access time?

Question

Assuming given filesystem is tracking Last Access Time (aka atime) -- which operations on a file cause atime to update?

As far as I know:

• opening existing file (and subsequent closing related handle/fd) does not update atime
• reading/writing file will update atime (I wonder if read-0-bytes operation does that)
• reading file security descriptor (via related Win32 API) does not update atime or other file attributes

Is there an exhaustive list of operations that update atime?

Answer 1

The last access time includes the last time the file or directory was written to, read from, or, in the case of executable files, run.

Other operations, like accessing the file to retrieve properties to show in Explorer or some other viewer, accessing the file to retrieve its icon etc. don't update last access time.

Refer to "GetFileTime - lpLastAccessTime", "How do I access a file without updating its last-access time?"

Update: Add test results of read/write 0 bytes and read/write 1 bytes.

Code used for testing:

void GetLastAccessTime(HANDLE hFile)
{
    FILETIME ftAccess;
    SYSTEMTIME stUTC, stLocal;

    printf("Get last access time\n");

    // Retrieve the file times for the file.
    if (!GetFileTime(hFile, NULL, &ftAccess, NULL))
        return;

    // Convert the last-write time to local time.
    FileTimeToSystemTime(&ftAccess, &stUTC);
    SystemTimeToTzSpecificLocalTime(NULL, &stUTC, &stLocal);

    // Build a string showing the date and time.
    wprintf(
        L"%02d/%02d/%d  %02d:%02d \n",
        stLocal.wMonth, stLocal.wDay, stLocal.wYear,
        stLocal.wHour, stLocal.wMinute);
}

int main()
{
    HANDLE tFile = INVALID_HANDLE_VALUE;

    printf("Open file\n");
    // Open file
    tFile = CreateFile(L"C:\\Users\\ritah\\Desktop\\test1.txt", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
    if (INVALID_HANDLE_VALUE == tFile)
    {
        printf("CreateFile fails with error: %d\n", GetLastError());
        getchar();
        return 0;
    }

    printf("Sleep 60 seconds\n");
    Sleep(60000);

    GetLastAccessTime(tFile);

    // Read 0 bytes
    printf("Read 0 bytes\n");
    WCHAR redBuf[10];
    DWORD redBytes = 0;
    if(!ReadFile(tFile, redBuf, 0, &redBytes, NULL))
    {
        printf("ReadFile fails with error: %d\n", GetLastError());
        getchar();
        return 0;
    }

    printf("Sleep 60 seconds\n");
    Sleep(60000);

    GetLastAccessTime(tFile);

    // Write 0 bytes
    printf("Write 0 bytes\n");
    WCHAR writeBuf[] = L"write test";
    DWORD writeBytes = 0;
    if(!WriteFile(tFile, writeBuf, 0, &writeBytes, NULL))
    {
        printf("WriteFile fails with error: %d\n", GetLastError());
        getchar();
        return 0;
    }

    printf("Sleep 60 seconds\n");
    Sleep(60000);

    GetLastAccessTime(tFile);

    getchar();
}

So, read/write 0 bytes doesn't update last access time.

Answer 2

Also you can use the method File.GetLastAccessTime(fileInfoLocation); before the code that will change the LastAccessTime and then after the code thats going to change the LastAccessTime you can use the method File.SetLastAccessTime(fileInfoLocation, originalLastAccessTime); to set it back to what it was though you need Administrative privileges for the SetLastAccessTime part if you want to change it to the original AKA run as admin. Heres some code for example:

FileInfo fileInfoLocation = new FileInfo(getAllExeLocation[l]);
                                                DateTime originalLastAccessTime = File.GetLastAccessTime(fileInfoLocation.FullName);//Save the LastAccessTime before it was changed by Icon.Extract Method
                                                exeIcon = Icon.ExtractAssociatedIcon(fileInfoLocation.FullName);//This changes LastAccessTime
                                                File.SetLastAccessTime(fileInfoLocation.FullName, originalLastAccessTime);//Set the LastAccessTime to the originalOne though it needs Privileges to do this one(run as admin) or Use Try-Catch statement