C# UInt64 减法问题

Question

Why subtraction with UInt64 data type sometimes error occurs. I reduce the number of seconds timespan with the result should be between 1 - 10, but the results of the system can be millions or even billions? Bugs?

private bool isReplayRequest(string kode, string rTs)
{
    if (System.Runtime.Caching.MemoryCache.Default.Contains(kode))
    {
        return true;
    }
    
    DateTime eStart = new DateTime(1970, 01, 01, 0, 0, 0, 0, DateTimeKind.Utc);
    TimeSpan cTs = DateTime.UtcNow - eStart;
    var stotalSeconds = Convert.ToUInt64(cTs.TotalSeconds);
    var rTotalSeconds = Convert.ToUInt64(rTs);
    
    if ((stotalSeconds - rTotalSeconds) > maxSeconds)
    {
        return true;
    }
    
    .... etc ....
}

Issue on line (stotalSeconds - rTotalSeconds)

Answer 1

Not sure this is the solution to your problem – just my first thought

By default the C# compiler does not check for arithmetic overflow

In Visual Studio you can enable this option in the properties of the project, build section, advanced settings

Outside Visual Studio here are the compiler settings

-checked

or

<CheckForOverflowUnderflow>true</CheckForOverflowUnderflow>

Fabio