Object Size

Question

Hi Can any one help me when i declare the object type variable how much space or memory will occupy it.....? and what is difference b/w Object and object in .net

Vulpes · Answer

All reference type objects are stored on the heap and the memory allocated is equal to the sum of the bytes needed for each of their instance fields plus overhead of 8 bytes (16 bytes on a 64-bit system). However for efficiency the fields are normally aligned on 4 (or 8) byte boundaries - consistent with a 32-bit or 64-bit CPU - and their order may also be rearranged by the CLR. This may mean that the memory needed for the fields is more than you would otherwise expect. The overhead contains a pointer to the object's 'type object' (every type is represented by a unique object of type System.Type) plus a 'sync block' index which is used when the object is the subject of a 'lock' statement (or Monitor.Enter) in a multi-threading scenario. As far as the System.Object type is concerned (for which C#'s 'object' keyword is just an alias) it has no fields and you'd therefore expect an object of that type to just contain overead. However for technical reasons it is necessary to be able to point to the first byte of an object's fields and the CLR therefore needs to allocate a single byte for objects which have no fields making a total of 9 on a 32-bit system or 17 on a 64-bit system. In practice because of alignment the next 3 (or 7 bytes) won't be used by the next object to be allocated so effectively the memory allocation is 12 (or 16) bytes.

Dorababu Meka · Answer

The size of an actual object doesn't include the size of any objects it references. The only things which are likely to end up on the large object heap are arrays and strings - other objects tends to be relatively small in themselves. Even an object with (say) 10 reference type variables (4 bytes each on x86) and 10 GUIDs (16 bytes each) is only going to take up about 208 bytes (there's a bit of overhead for the type reference and sync block). Likewise when thinking about the size of an array don't forget that if the element type is a reference type then it's only the size of the references that count for the array itself. In other words even if you've got an array with 20000 elements the size of the array object itself will only be just over 80K (on x86) even if it references a lot more data No difference C# provides synonyms for the primitives defined by the CLR. System.String -> string System.Int64 -> long System.Object -> object  like wise