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General Question About Structs and StackA struct is stored on the stack and a class on the heap. A struct is a value type while a class is a reference type. Question: What if a struct contains a string property(variable). The string would be a reference type being contained in a value type. Would this filter up and cause the stack to now be a reference type placed on the heap or would it still be on the stack with a pointer used internally to point to a preallocated string object on the heap? The reason for the question is because almost all examples related to stacks and discussing the speed benefits never show anything in the stack other than value types (which a internally structs themselves like int). I am creating a large binary tree and currently use classes to implement it. There are no problems with the code, but if I could see a major performance gain by switching the classes to structs I would do it. What do you think? -Greg Hi,
The struct will always remain on the stack, that's why you can not assign null to the structure nevertheless you have a reference variable in it. If you want to move the structure to the heap to test performance you can use a weakReference to store the value type. There are some details on the secions 11.3.1, 4.1 and 4.2 of the c# specification. Hope this helps to understand. Salva Show quote "gmccallum" wrote: > General Info: > A struct is stored on the stack and a class on the heap. > A struct is a value type while a class is a reference type. > > Question: > What if a struct contains a string property(variable). The string would > be a reference type being contained in a value type. Would this filter > up and cause the stack to now be a reference type placed on the heap > or would it still be on the stack with a pointer used internally to point > to a preallocated string object on the heap? > > The reason for the question is because almost all examples related to > stacks and discussing the speed benefits never show anything in the > stack other than value types (which a internally structs themselves like int). > > I am creating a large binary tree and currently use classes to implement it. > There are no problems with the code, but if I could see a major performance > gain by switching the classes to structs I would do it. > > What do you think? > > -Greg So if the struct will remain on the stack (where I want it), then how is it
still treated as a value type when it contains a reference type. Does this seriously affect performance. example struct { int x; // value type string s; // ref type } -Greg McCallum (MCSD) Show quote "Salvador" wrote: > Hi, > > The struct will always remain on the stack, that's why you can not assign > null to the structure nevertheless you have a reference variable in it. > If you want to move the structure to the heap to test performance you can > use a weakReference to store the value type. > > There are some details on the secions 11.3.1, 4.1 and 4.2 of the c# > specification. > > Hope this helps to understand. > Salva > > "gmccallum" wrote: > > > General Info: > > A struct is stored on the stack and a class on the heap. > > A struct is a value type while a class is a reference type. > > > > Question: > > What if a struct contains a string property(variable). The string would > > be a reference type being contained in a value type. Would this filter > > up and cause the stack to now be a reference type placed on the heap > > or would it still be on the stack with a pointer used internally to point > > to a preallocated string object on the heap? > > > > The reason for the question is because almost all examples related to > > stacks and discussing the speed benefits never show anything in the > > stack other than value types (which a internally structs themselves like int). > > > > I am creating a large binary tree and currently use classes to implement it. > > There are no problems with the code, but if I could see a major performance > > gain by switching the classes to structs I would do it. > > > > What do you think? > > > > -Greg Hi,
Maybe this can help to understand, The memory slot for a variable is stored on either the stack or the heap. It depends on the context in which it is declared: Each local variable (ie one declared in a method) is stored on the stack. That includes reference type variables - the variable itself is on the stack, but remember that the value of a reference type variable is only a reference (or null), not the object itself. Method parameters count as local variables too, but if they are declared with the ref modifier, they don't get their own slot, but share a slot with the variable used in the calling code. See my article on parameter passing for more details Instance variables for a reference type are always on the heap. That's where the object itself "lives". Instance variables for a value type are stored in the same context as the variable that declares the value type. The memory slot for the instance effectively contains the slots for each field within the instance. That means (given the previous two points) that a struct variable declared within a method will always be on the stack, whereas a struct variable which is an instance field of a class will be on the heap. Every static variable is stored on the heap, regardless of whether it's declared within a reference type or a value type. There is only one slot in total no matter how many instances are created. Best regards SAlva Show quote "gmccallum" wrote: > So if the struct will remain on the stack (where I want it), then how is it > still > treated as a value type when it contains a reference type. Does this > seriously > affect performance. > > example > struct { > int x; // value type > string s; // ref type > } > > -Greg McCallum (MCSD) > > "Salvador" wrote: > > > Hi, > > > > The struct will always remain on the stack, that's why you can not assign > > null to the structure nevertheless you have a reference variable in it. > > If you want to move the structure to the heap to test performance you can > > use a weakReference to store the value type. > > > > There are some details on the secions 11.3.1, 4.1 and 4.2 of the c# > > specification. > > > > Hope this helps to understand. > > Salva > > > > "gmccallum" wrote: > > > > > General Info: > > > A struct is stored on the stack and a class on the heap. > > > A struct is a value type while a class is a reference type. > > > > > > Question: > > > What if a struct contains a string property(variable). The string would > > > be a reference type being contained in a value type. Would this filter > > > up and cause the stack to now be a reference type placed on the heap > > > or would it still be on the stack with a pointer used internally to point > > > to a preallocated string object on the heap? > > > > > > The reason for the question is because almost all examples related to > > > stacks and discussing the speed benefits never show anything in the > > > stack other than value types (which a internally structs themselves like int). > > > > > > I am creating a large binary tree and currently use classes to implement it. > > > There are no problems with the code, but if I could see a major performance > > > gain by switching the classes to structs I would do it. > > > > > > What do you think? > > > > > > -Greg Salvador <Salva***@discussions.microsoft.com> wrote:
> Maybe this can help to understand, <snip>Hopefully it will have done, but while I don't have any problem with people quoting my web articles in news posts, it would be nice to at least post a link to the original at the same time. http://www.pobox.com/~skeet/csharp/memory.html -- Jon Skeet - <sk***@pobox.com> http://www.pobox.com/~skeet If replying to the group, please do not mail me too So if the struct will remain on the stack (where I want it), then how is it
still treated as a value type when it contains a reference type. Does this seriously affect performance. example struct { int x; // value type string s; // ref type } -Greg McCallum (MCSD) Show quote "Salvador" wrote: > Hi, > > The struct will always remain on the stack, that's why you can not assign > null to the structure nevertheless you have a reference variable in it. > If you want to move the structure to the heap to test performance you can > use a weakReference to store the value type. > > There are some details on the secions 11.3.1, 4.1 and 4.2 of the c# > specification. > > Hope this helps to understand. > Salva > > "gmccallum" wrote: > > > General Info: > > A struct is stored on the stack and a class on the heap. > > A struct is a value type while a class is a reference type. > > > > Question: > > What if a struct contains a string property(variable). The string would > > be a reference type being contained in a value type. Would this filter > > up and cause the stack to now be a reference type placed on the heap > > or would it still be on the stack with a pointer used internally to point > > to a preallocated string object on the heap? > > > > The reason for the question is because almost all examples related to > > stacks and discussing the speed benefits never show anything in the > > stack other than value types (which a internally structs themselves like int). > > > > I am creating a large binary tree and currently use classes to implement it. > > There are no problems with the code, but if I could see a major performance > > gain by switching the classes to structs I would do it. > > > > What do you think? > > > > -Greg >> would it still be on the stack with a pointer used internally to point As far as I know, that is the case. I see no advantage, and lot of> to a preallocated string object on the heap? problems if it were handled any other way. Note, that this is exactly know a string as a local varaible is handled. Show quote "gmccallum" <gmccal***@discussions.microsoft.com> wrote in message news:A39D617B-922E-4027-A6BC-D645A440DC9F@microsoft.com... > General Info: > A struct is stored on the stack and a class on the heap. > A struct is a value type while a class is a reference type. > > Question: > What if a struct contains a string property(variable). The string would > be a reference type being contained in a value type. Would this filter > up and cause the stack to now be a reference type placed on the heap > or would it still be on the stack with a pointer used internally to point > to a preallocated string object on the heap? > > The reason for the question is because almost all examples related to > stacks and discussing the speed benefits never show anything in the > stack other than value types (which a internally structs themselves like int). > > I am creating a large binary tree and currently use classes to implement it. > There are no problems with the code, but if I could see a major performance > gain by switching the classes to structs I would do it. > > What do you think? > > -Greg Thanks James and Salvador. I am trying the get the latest version of the c#
specs from Microsoft, but it appears to be unavailable at the moment. If it turns out the stack is handled as stated below for a reference type being included in it, then this would defintely be more effiecient than using the class when I don't care if it is sealed and don't plain to use it as a base class to anything. - Greg McCallum Show quote "James Curran" wrote: > >> would it still be on the stack with a pointer used internally to point > > to a preallocated string object on the heap? > > As far as I know, that is the case. I see no advantage, and lot of > problems if it were handled any other way. Note, that this is exactly know > a string as a local varaible is handled. > > > "gmccallum" <gmccal***@discussions.microsoft.com> wrote in message > news:A39D617B-922E-4027-A6BC-D645A440DC9F@microsoft.com... > > General Info: > > A struct is stored on the stack and a class on the heap. > > A struct is a value type while a class is a reference type. > > > > Question: > > What if a struct contains a string property(variable). The string would > > be a reference type being contained in a value type. Would this filter > > up and cause the stack to now be a reference type placed on the heap > > or would it still be on the stack with a pointer used internally to point > > to a preallocated string object on the heap? > > > > The reason for the question is because almost all examples related to > > stacks and discussing the speed benefits never show anything in the > > stack other than value types (which a internally structs themselves like > int). > > > > I am creating a large binary tree and currently use classes to implement > it. > > There are no problems with the code, but if I could see a major > performance > > gain by switching the classes to structs I would do it. > > > > What do you think? > > > > -Greg > > > Hi,
A lot of confusion has been wrought by people explaining the difference between value types and reference types as "value types go on the stack, reference types go on the heap, this is simply untrue. Check my previous message. Hope this helps to solve a common problem. Salva Show quote "gmccallum" wrote: > Thanks James and Salvador. I am trying the get the latest version of the c# > specs from Microsoft, but it appears to be unavailable at the moment. > > If it turns out the stack is handled as stated below for a reference type > being included in it, then this would defintely be more effiecient than using > the class when I don't care if it is sealed and don't plain to use it as a > base class to anything. > > - Greg McCallum > > > "James Curran" wrote: > > > >> would it still be on the stack with a pointer used internally to point > > > to a preallocated string object on the heap? > > > > As far as I know, that is the case. I see no advantage, and lot of > > problems if it were handled any other way. Note, that this is exactly know > > a string as a local varaible is handled. > > > > > > "gmccallum" <gmccal***@discussions.microsoft.com> wrote in message > > news:A39D617B-922E-4027-A6BC-D645A440DC9F@microsoft.com... > > > General Info: > > > A struct is stored on the stack and a class on the heap. > > > A struct is a value type while a class is a reference type. > > > > > > Question: > > > What if a struct contains a string property(variable). The string would > > > be a reference type being contained in a value type. Would this filter > > > up and cause the stack to now be a reference type placed on the heap > > > or would it still be on the stack with a pointer used internally to point > > > to a preallocated string object on the heap? > > > > > > The reason for the question is because almost all examples related to > > > stacks and discussing the speed benefits never show anything in the > > > stack other than value types (which a internally structs themselves like > > int). > > > > > > I am creating a large binary tree and currently use classes to implement > > it. > > > There are no problems with the code, but if I could see a major > > performance > > > gain by switching the classes to structs I would do it. > > > > > > What do you think? > > > > > > -Greg > > > > > > What you state is true, you are describing the concept of stack frames.
However the c# documentation states that classes are stored on the heap which would mean in the current stack frame would exist a pointer to a memory block on the heap which would contain the actual data. A struct however (when it contains only value types) would be totally stored on the stack with no pointers to the heap. Which would be a major speed enhancement. The problem I see is that the moment you create a reference type within the struct then one of three things could occur: 1) the entire struct would be relocated to heap with a pointer placed in the stack frame to hold its location. (BAD) 2) the struct would remain on the stack with a pointer used to contain the address of the actual string data which has be placed on the heap. (SO SO) 3) the struct would remain on the stack and all the variables defined within would remain entirely on the stack as well. (no far pointers - EXCELLANT). I am beginning to think that option 2 is what happens, but I was hoping for option 3. -Greg McCallum Hi Greg,
It is interesting, so I run the CLR Profiler http://msdn.microsoft.com/netframework/downloads/tools/default.aspx You can see the heap there, you can filter to show when a new object is loaded on the heap, after creating an instance of the struct and populating the string nothing appared on the heap. Maybe this means good news for you. Give it a try and keep me posted if you find anything interesting. My email is Salvapat***@yahoo.co.uk, is good to have people with good knowledge around. cheers Salva Show quote "gmccallum" wrote: > What you state is true, you are describing the concept of stack frames. > > However the c# documentation states that classes are stored on the heap > which would mean in the current stack frame would exist a pointer to a memory > block on the heap which would contain the actual data. A struct however > (when it contains only value types) would be totally stored on the stack with > no pointers to the heap. Which would be a major speed enhancement. > > The problem I see is that the moment you create a reference type within the > struct then one of three things could occur: > 1) the entire struct would be relocated to heap with a pointer placed in the > stack frame to hold its location. (BAD) > 2) the struct would remain on the stack with a pointer used to contain the > address of the actual string data which has be placed on the heap. (SO SO) > 3) the struct would remain on the stack and all the variables defined within > would remain entirely on the stack as well. (no far pointers - EXCELLANT). > > I am beginning to think that option 2 is what happens, but I was hoping for > option 3. > > -Greg McCallum > I will do so. Thanks for the interaction.
-Greg Show quote "Salvador" wrote: > Hi Greg, > > It is interesting, so I run the CLR Profiler > > http://msdn.microsoft.com/netframework/downloads/tools/default.aspx > > You can see the heap there, you can filter to show when a new object is > loaded on the heap, after creating an instance of the struct and populating > the string nothing appared on the heap. Maybe this means good news for you. > Give it a try and keep me posted if you find anything interesting. > > My email is Salvapat***@yahoo.co.uk, is good to have people with good > knowledge around. > > cheers > Salva > > > "gmccallum" wrote: > > > What you state is true, you are describing the concept of stack frames. > > > > However the c# documentation states that classes are stored on the heap > > which would mean in the current stack frame would exist a pointer to a memory > > block on the heap which would contain the actual data. A struct however > > (when it contains only value types) would be totally stored on the stack with > > no pointers to the heap. Which would be a major speed enhancement. > > > > The problem I see is that the moment you create a reference type within the > > struct then one of three things could occur: > > 1) the entire struct would be relocated to heap with a pointer placed in the > > stack frame to hold its location. (BAD) > > 2) the struct would remain on the stack with a pointer used to contain the > > address of the actual string data which has be placed on the heap. (SO SO) > > 3) the struct would remain on the stack and all the variables defined within > > would remain entirely on the stack as well. (no far pointers - EXCELLANT). > > > > I am beginning to think that option 2 is what happens, but I was hoping for > > option 3. > > > > -Greg McCallum > > gmccallum wrote:
> General Info: This isn't precisely correct. When you create a stack in a function, it's> A struct is stored on the stack and a class on the heap. (usually) on the stack, but it's possible to copy it to the heap, which is what happens when you put it in a container class. > A struct is a value type while a class is a reference type. This is correct.> Question: no.> What if a struct contains a string property(variable). The string > would > be a reference type being contained in a value type. Would this > filter > up and cause the stack to now be a reference type placed on the heap > or would it still be on the stack with a pointer used internally to Yes, although, I disagree with the use of the word "preallocated" there.> point > to a preallocated string object on the heap? There's nothing preallocated. It's just some memory on the heap for the string, and every reference to it is, effectively, a pointer, including the one in the struct. > The reason for the question is because almost all examples related to Ultimately, this has to to with garbage collection, which a struct will not,> stacks and discussing the speed benefits never show anything in the > stack other than value types (which a internally structs themselves > like int). in some cases, be subject to. > I am creating a large binary tree and currently use classes to I do not think you will see a speed improvement by switching to structs.> implement it. There are no problems with the code, but if I could see > a major performance gain by switching the classes to structs I would > do it. You may experience a degradation. Generally, however, one must test to be sure, especially in the area of performance, because so many factors can come into play that you may not know about. -- Reginald Blue "I have always wished that my computer would be as easy to use as my telephone. My wish has come true. I no longer know how to use my telephone." - Bjarne Stroustrup (originator of C++) [quoted at the 2003 International Conference on Intelligent User Interfaces] gmccallum <gmccal***@discussions.microsoft.com> wrote:
> General Info: No, it's not that simple.> A struct is stored on the stack and a class on the heap. See http://www.pobox.com/~skeet/csharp/memory.html (Salvador's already quoted most of it, but it's better to see the whole thing in context.) > A struct is a value type while a class is a reference type. That is certainly true.-- Jon Skeet - <sk***@pobox.com> http://www.pobox.com/~skeet If replying to the group, please do not mail me too  |
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