c# - Marshal.StructureToPtr <-> PtrToStructure rounds DateTime field -

the structure

public struct tick : iequatable<tick> {     public datetime date;     public decimal price;     public int volume;      public tick(datetime date, decimal price, int volume)     {         this.date = date;         this.price = price;         this.volume = volume;     }      public override bool equals(object obj)     {         var other = (tick)obj;         return this.date == other.date && this.price == other.price && this.volume == other.volume;     }     public bool equals(tick other)     {         return this.date == other.date && this.price == other.price && this.volume == other.volume;     } } 

is changed in test:

    [test]     public void marshaldoesntroundsdatetime() {         (int = 0; < 1000; i++)         {             var = new tick(datetime.now.addseconds(i), i, i);             var now2 = now;              var ticks = new tick[1];             unsafe             {                 fixed (tick* ptr = &ticks[0])                 {                     marshal.structuretoptr(now2, (intptr)ptr, false);                     now2 = (tick)marshal.ptrtostructure((intptr)ptr, typeof(tick));                     assert.areequal(now.date.ticks, now2.date.ticks);                 }             }         }     }     expected: 635719676058860752   was:  635719676058860000 

what going on? why datetime rounded after marshalling? documented somewhere?

marshal.structuretoptr() intended marshal data unmanaged code. there multiple "standards" dates in native code, none close in range , accuracy datetime. clr designers went com interop standard, exposed datetime.tooadate().

as can tell reference source, can no more accurate 1 msec. datetime accurate 0.1 usec. inevitably last 4 digits looking @ must 0.

it not clear why doing or why matters. guessing, keep in mind marshal.structuretoptr() seems attractive way serialize .net data.