C# Why structure take less memory compare to class

Question

C# Why structure take less memory compare to class

T.Zacks 3,996

Looking for list of points for which structure take less memory compare to class. i have checked these links
https://social.msdn.microsoft.com/Forums/vstudio/en-US/ff7fbffc-c6d3-474d-ad2c-8a2415852c00/why-they-say-struct-takes-lesser-memory-than-class-objects?forum=csharpgeneral

https://stackoverflow.com/questions/2761742/overhead-of-class-vs-structure-in-c
http://clarkkromenaker.com/post/csharp-structs/

another question is what is default in c# By Value or By Reference?
if by reference then how could i prove it just running a sample code. please share a sample code. thanks

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Answer 1

Bruce (SqlWork.com) 74,146

C# structs are allocated on the stack unless "boxed". when "boxed" they are copied to the heap and must be garbage collected like a class instance. also as they do not implement inheritance, the methods do not require a vtable.

the C# default is pass by value. to pass by ref, you use the ref key word

using System;    
    
int i = 0;    
    
callbyvalue(i);    
Console.WriteLine(i); // 0    
    
callbyref(ref i);    
Console.WriteLine(i); // 2    
    
void callbyvalue(int x)    
{    
 x = 1;    
}    
    
void callbyref(ref int x)    
{    
 x = 2;    
}

T.Zacks 3,996 Reputation points

2022-09-17T15:08:59.33+00:00

Thanks for your reply but did not mention why structs take less memory compare to class? just it stored in stack and that is why it takes less memory.
please elaborate this point if possible. thanks
Bruce (SqlWork.com) 74,146 Reputation points

2022-09-17T15:33:47.667+00:00

allocations in the heap (boxed) require extra memory for the heap management. Also classes require a vtable data structure.

This memory overhead is small, but for tiny objects it may be bigger than the object.

But stack vs heap and pass by copy is the significant difference. With boxed objects pass by value is a copy of the variable reference rather than data.
T.Zacks 3,996 Reputation points

2022-09-17T16:56:05.483+00:00

Thank you again Sir for your reply. please elaborate this what you said with a example C# structs are allocated on the stack unless "boxed" please provide sample which show how to box/ unbox data for Record type.

please explain this point with a sample code -> With boxed objects pass by value is a copy of the variable reference rather than data.

waiting for your sample code just to see how to box and unbox Record type. when Record type will be stored on heap instead of stack. thanks
Jack J Jun 25,291 Reputation points

2022-09-21T07:00:58.017+00:00

@T.Zacks , you could refer to the Microsoft doc boxing-and-unboxing to know how to box and unbox value type.

Guru Prasad 0

@T.Zacks may be I tried something to understand the expectation. Not sure though.

class HelloWorld {
      static void Main() {
          
          ObjectHavingStruct obj=new ObjectHavingStruct();
          accessStruct(obj);
          Console.WriteLine(obj.stct.name);
    }
  
      static void accessStruct(ObjectHavingStruct obj1){
          obj1.stct.name = "John";
      }
}

    public struct myStruct{
        public string name;
        public int age;
    }

class ObjectHavingStruct
{
    public myStruct stct=new myStruct();
    
    public ObjectHavingStruct(){
        stct.name = "Robert";
    }
}

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C# Why structure take less memory compare to class

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