time_t到.NET的转换

方法1：

public DateTime UNIXtoDateTime(long seconds)

{

　　double secs = Convert.ToDouble(seconds);
DateTime dt = new DateTime(1970, 1, 1, 0, 0, 0).AddSeconds(secs);
return System.TimeZone.CurrentTimeZone.ToLocalTime(dt);
} 

方法2：

public sealed class ConvertTime
{
/// <summary>
/// Private constructor to prevent the class from being instantiated.
/// </summary>
private ConvertTime() {}

private static DateTime origin = System.TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(1970, 1, 1, 0, 0, 0));

/// <summary>
/// time_t is an int representing the number of seconds since Midnight UTC 1 Jan 1970 on the Gregorian Calendar.
/// </summary>
/// <param name="time_t"></param>
/// <returns></returns>
public static DateTime ToDateTime(int time_t)
{
DateTime convertedValue = origin + new TimeSpan(time_t * TimeSpan.TicksPerSecond);
if (System.TimeZone.CurrentTimeZone.IsDaylightSavingTime(convertedValue) == true)
{
System.Globalization.DaylightTime daylightTime = System.TimeZone.CurrentTimeZone.GetDaylightChanges(convertedValue.Year);
convertedValue = convertedValue + daylightTime.Delta;
}
return convertedValue;
}

/// <summary>
/// time_t is an int representing the number of seconds since Midnight UTC 1 Jan 1970 on the Gregorian Calendar.
/// </summary>
/// <param name="time"></param>
/// <returns></returns>
public static int To_time_t(DateTime time)
{
DateTime convertedValue = time;
if (System.TimeZone.CurrentTimeZone.IsDaylightSavingTime(convertedValue) == true)
{
System.Globalization.DaylightTime daylightTime = System.TimeZone.CurrentTimeZone.GetDaylightChanges(convertedValue.Year);
convertedValue = convertedValue - daylightTime.Delta;
}
long diff = convertedValue.Ticks - origin.Ticks;
return (int)(diff / TimeSpan.TicksPerSecond);
}
}

Also  you can convert filetime or oledate to System.DateTime.
FILETIME to/from System.DateTime
Use System.DateTime.FromFileTime() and System.DateTime.ToFileTime().
OLE date to/from System.DateTime
Use System.DateTime.FromOADate() and System.DateTime.ToOADate(). 

来自：
http://blog.csdn.net/RedRiver331/archive/2006/07/02/865231.aspx