using WriteFile windows API in c#

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern IntPtr CreateFile(
    string lpFileName,
    uint dwDesiredAccess,
    uint dwShareMode,
    IntPtr lpSecurityAttributes,
    uint dwCreationDisposition,
    uint dwFlagsAndAttributes,
    IntPtr hTemplateFile);

[DllImport("kernel32.dll", BestFitMapping = true, CharSet = CharSet.Ansi)]
public static extern bool WriteFile(
    IntPtr hFile,
    System.Text.StringBuilder lpBuffer,
    uint nNumberOfBytesToWrite,
    out uint lpNumberOfBytesWritten,
    [In] ref System.Threading.NativeOverlapped lpOverlapped);

_FileHandle = CreateFile(_CSVFileName, 0x40000000, 0x00000001, IntPtr.Zero, 4, 0x00000080, IntPtr.Zero);

WriteFile(_FileHandle, oSTR, LenToWrite, out LenWritten, ref OverLap);