Why is the bool type 4 bytes it's a wast of memory..
in [CSharp]
|
Prev: Using Delegates?
Next: Drag & Drop text
From: Arne Vajhøj on 14 Jun 2010 22:29 On 14-06-2010 19:25, Tom Shelton wrote: > Rudy Velthuis wrote on 6/14/2010 : >> Arne Vajh�j wrote: >>> On 28-05-2010 03:34, Tony Johansson wrote: >>>> Is it anyone that might have a good explanation why the designor of >>>> .NET made a bool 4 bytes. >>>> I mean it's just a wast of memory. >>> >>> Somebody at Microsoft made a decision. >> >> Er... I just checked, and >> Console.WriteLine(sizeof(bool)); >> printed 1 for me. On 32 bit Windows. I don't quite understand what the >> fuss is all about. <g> >> >> Of course, if the bool is part of an aligned struct, the padding bytes >> may make the offset of the next member (say, an Int32) >> <offset of boolean> + 4. But a bool itself is only 1 byte in size, >> AFAICT. If the next member is a double, the padding can even be 7 >> bytes, but that does not make the bool 8 bytes in size. >> >> IOW, this probably has a size of 16 bytes: >> >> struct Foo >> { >> bool b; >> double d; >> } > > sizeof represents the .net runtime size. It will return 1. > Marshal.SizeOf (typeof(bool)) will return 4, as the marshaller converts > a bool to 4 bytes when passed to native code... But that means that BOOL in Win32 C is 4 bytes not that bool in C# is 4 bytes. But it may be the background for Tony's book. Arne
From: Arne Vajhøj on 14 Jun 2010 22:27 On 14-06-2010 19:08, Rudy Velthuis wrote: > Arne Vajh�j wrote: >> On 28-05-2010 03:34, Tony Johansson wrote: >>> Is it anyone that might have a good explanation why the designor of >>> .NET made a bool 4 bytes. > > Sorry, I can't see the orginal message, but (at least on my Windows > 32bit) sizeof(bool) is 1, so I wonder what this discussion is about.<g> Good question. I guess the best answer is: Tony's book ! :-) Arne
From: Rudy Velthuis on 15 Jun 2010 06:40 Tom Shelton wrote: > > IOW, this probably has a size of 16 bytes: > > > > struct Foo > > { > > bool b; > > double d; > > } > > sizeof represents the .net runtime size. It will return 1. > Marshal.SizeOf (typeof(bool)) will return 4, as the marshaller > converts a bool to 4 bytes when passed to native code... Ah, that's a different case. If you push a boolean on the stack, as a function parameter, it will take up 4 bytes, indeed (in a 32 bit context). -- Rudy Velthuis http://rvelthuis.de "Pain is certain, suffering is optional." -- Buddha
From: Rudy Velthuis on 15 Jun 2010 06:41 Arne Vajh�j wrote: > On 14-06-2010 19:11, Rudy Velthuis wrote: > > Patrice wrote: > >>> 1 byte incl. padding 4 bytes incl. padding > > > > 1 boolean 4 bytes 4 bytes > > > > 4 boolean 4 bytes 16 bytes > > > > > > But then those booleans are not all aligned any more > > > > Natural alignment means that a type is aligned on a multiple of its > > own size (in bytes), so bytes are always naturally aligned, by > > definition. > > We already covered that part a week ago. I missed that, sorry. -- Rudy Velthuis http://rvelthuis.de Parkinson's Law: Work expands to fill the time available for its completion.
From: Arne Vajhøj on 15 Jun 2010 22:00
On 15-06-2010 06:41, Rudy Velthuis wrote: > Arne Vajh�j wrote: >> On 14-06-2010 19:11, Rudy Velthuis wrote: >>> Patrice wrote: >>>>> 1 byte incl. padding 4 bytes incl. padding >>>>> 1 boolean 4 bytes 4 bytes >>>>> 4 boolean 4 bytes 16 bytes >>>> >>>> But then those booleans are not all aligned any more >>> >>> Natural alignment means that a type is aligned on a multiple of its >>> own size (in bytes), so bytes are always naturally aligned, by >>> definition. >> >> We already covered that part a week ago. > > I missed that, sorry. Your main point was still a very good catch! Arne |