|
I agree, Chris!
But, since DateTime is a value type, so, there should be an internal copy of current time created by struct DateTime struct itself, and during assignment to variable abc, abc is another copy of "current time", so there are two copies, right?
regards,
George
|
|
|
|
|
George_George wrote: But, since DateTime is a value type, so, there should be an internal copy of current time created by struct DateTime struct itself, and during assignment to variable abc, abc is another copy of "current time", so there are two copies, right?
If DateTime is a value type, then it's going to be copied when it is returned. You're talking about a collection of a handful of ints. I don't see that as a big deal, do you ?
Christian Graus
Please read this if you don't understand the answer I've given you
"also I don't think "TranslateOneToTwoBillion OneHundredAndFortySevenMillion FourHundredAndEightyThreeThousand SixHundredAndFortySeven()" is a very good choice for a function name" - SpacixOne ( offering help to someone who really needed it ) ( spaces added for the benefit of people running at < 1280x1024 )
|
|
|
|
|
I agree with you Chris. My purpose is just to understand how things work from CLR principle. BTW, you mentioned -- "collection of a handful of ints", you mean the DateTime is represented by a couple of int type and the foot print is small?
regards,
George
|
|
|
|
|
Does it really matter? With all the bloat built into Windows and .NET in general whats a few bytes here or there
Bob
Ashfield Consultants Ltd
|
|
|
|
|
Hi Bob,
I just want to practice my understanding of C# concepts.
regards,
George
|
|
|
|
|
DateTime.Now is a static property and returns a new instance of a DateTime object. The only thing in memory is the newly allocated (and returned) DateTime object.
Stop over-analyzing this crap and do some real work.
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997 ----- "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001
|
|
|
|
|
Thanks John,
What is your comments to my original question? There is additional copy, right?
regards,
George
|
|
|
|
|
I suppose, but it's the same as any value type.
|
|
|
|
|
Thanks PIEBALDconsult,
So, you agree with my points (1) and (2) in original question post? And DateTime abc = DateTime.Now statement will create two copies of values?
regards,
George
|
|
|
|
|
Only as far as something like:
public static DateTime
Now
{
get
{
DateTime temp ;
return ( temp ) ;
}
}
(Which may not even be the case.)
In such a method, the value from the local variable gets copied to the receiving variable, so, yes, there are two variables containing the value, but I don't understand why you're asking.
|
|
|
|
|
Thanks PIEBALDconsult,
Question answered. I am just interesting in some techniques, not the real value.
I think understanding of how it works internally will facilitate my grasping of the whole CLR.
regards,
George
|
|
|
|
|
Temporarily yes, but even then it simply does a quadword copy in debug mode; it's very possible .NET optimizes this away in release mode so there is only one struct instance.
The temporary internal instance is required so the property has something to return. But it is discarded (unless optimized away) as soon as the new value is set.
Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke
|
|
|
|
|
Agree, thanks Joe!
regards,
George
|
|
|
|
|
There are actually several different values created when calling the Now property. The Now property calls UtcNow and ToLocalTime, UtcNow calls GetSystemTimeAsFileTime, ToLocalTime calls TimeZone.CurrentTimeZone.ToLocalTime, et.c.
However, as all those values are value types, the memory is allocated on the stack. The allocation is done when the stack frame is created for each call, and actually doesn't take any extra time at all. So, the only work really done is actually moving the value, which is a single machine instruction.
Despite everything, the person most likely to be fooling you next is yourself.
modified on Tuesday, June 10, 2008 4:43 AM
|
|
|
|
|
Thanks Guffa,
What do you mean "moving the value"? Could you show more description please why value type copy is just "moving the value" please?
regards,
George
|
|
|
|
|
The code "DateTime abc = DateTime.Now;" results in this IL code:
call valuetype DateTime DateTime::get_Now()<br />
stloc.2
The first instruction is the call to the property and second instruction stores the return value from the call into the variable abc. That's all. No extra value, no extra nothing, just a simple call that returns a simple value.
Despite everything, the person most likely to be fooling you next is yourself.
|
|
|
|
|
Thanks Guffa,
I think in more details -- the first call will put a new instance on the evaluation stack, and the 2nd call will load the new instance from the evaluation stack into the variable, correct?
regards,
George
|
|
|
|
|
Yes, that is correct, if you by "call" mean "instruction".
Despite everything, the person most likely to be fooling you next is yourself.
|
|
|
|
|
Thanks Guffa!
I understand the operations on stack now. Compared with variable instance on heap, generally speaking why operations on stack is better?
regards,
George
|
|
|
|
|
George_George wrote: Compared with variable instance on heap, generally speaking why operations on stack is better?
Because allocation and deallocation of the memory doesn't cost a thing. The memory is allocated by just making a larger stack frame when the method starts, and deallocation happens when the stack frame is removed. There is no garbage collection involved in freeing the memory.
This of course only applies to value types. Reference types are always allocated on the heap, even if the reference to it is on the stack.
Despite everything, the person most likely to be fooling you next is yourself.
|
|
|
|
|
Thanks Guffa,
So, you think GC is the major bottleneck of performance compared with stack variable and heap variable?
regards,
George
|
|
|
|
|
It probably is a waste but you need an instance of the DateTime struct to exist to be able to get the value! The other way would be for the Now property getter to be a method and require an out parameter. This would make things really complicated if you needed to do a simple calculation and didn't need a variable for the Now value.
The overhead is really very small indeed - personally I wouldn't waste my time on such minor details.
Dave
|
|
|
|
|
DaveyM69 wrote: It probably is a waste but you need an instance of the DateTime struct to exist to be able to get the value!
No, the Now property is static, so there is no instance existing before calling the property. The "DateTime" in "DateTime.Now" is just a specification of the class, it's not a value.
Despite everything, the person most likely to be fooling you next is yourself.
|
|
|
|
|
Guffa wrote: the Now property is static, so there is no instance existing before calling the property
I understand that. What I meant is the Now property getter returns a new struct of type DateTime
Dave
|
|
|
|
|
Ok, then it sounds like you think that you get the DateTime value from an instance of the DateTime struct, while they are infact the same thing.
It's pretty obvious that you need an instance of DateTime to have an instance of DateTime, if you don't have an instance of DateTime you don't have an instance of DateTime. It's actually so obvious that it sounds silly to say it...
Despite everything, the person most likely to be fooling you next is yourself.
|
|
|
|