Memory management in Dot net

Sharad Gupta

public static void Main()
{
string a ="abc";
string b=a;
a="xyz";
}
In this example, what is structure of memory, taken by these variable.

11 Replies

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Vulpes14y ago
Accepted answer
A variable of a particular type can only refer to one instance of that type at a time.

So, when 'a' is assigned a reference (effectively a pointer) to the string "xyz", it overwrites the reference which it previously contained to "abc".
Andy Manitara14y ago
1. Memory address -   Value
---------------------------------------
a -> #0x8f5c       "abc"


        a = "abc"

2.   Memory address -   Value
---------------------------------------
a,b -> #0x8f5c       "abc"

          a = b

3. Memory address -   Value
---------------------------------------
b -> #0x8f5c       "abc"
a -> #0x6f4e       "xyz"

          a = "xyz"

Something like that..
Shivanand Arur14y ago
Basically what happens is....

When you write as a = "abc", then a pointer "a" is created on stack which points to the String Object created on heap (lets say the memory address is 100 ) which contains value "abc".
For example.... a (points to address) -------> 100(This address contains value abc)

When you write b = a, then another pointer "b" is created on the thread stack which also points to the same memory address (100) which contains value "abc".
For example....
a (points to address) -------> 100 and
b(also points to the same memory address) -------> 100

Now when you write a = "xyz", then the "a" pointer starts pointing to another memory area which is created in the heap (say the memory address is 101)
For example....
a (points to address) -------> 101( This address contains value xyz )

So now when you write Console.WriteLine(a); you will get the output as "xyz" instead of "abc".

Hope this helps you.
Please mark the Answer an ACCEPTED IF IT HELPS YOU.

Thank you.
Sharad Gupta14y ago
When 'a' is assigned a reference (effectively a pointer) to the string "xyz", it overwrites the reference which it previously contained to "abc".

then what happen ......................

It(a) override the same memory area which is previously contained by abc or not..
Andy Manitara14y ago
Technically "abc" still on the heap in a random address, just no longer referenced by string a. String b points to "abc", and string a now points to a new entry in the heap "xyz"
Shivanand Arur14y ago
Hey Sharad Gupta, can you please mark the answer as Accepted if it has helped you... I think the answers, Vulpes has given are completely correct and very helpful....

Thank you.
Shivanand Arur14y ago
at the last line in ur code... A refers to the area where xyz is stored...
Sharad Gupta14y ago
What? a referencing the both abc and xyz value or only xyz.
Vulpes14y ago
All string literals such as "abc" and "xyz" are stored in a special area of the heap known as the intern pool.

The local variables 'a' and 'b' are stored on the stack.

However, 'a' will initially contain a reference to where "abc" is stored in the intern pool and 'b' will also contain exactly the same reference.

When 'a' is subsequently assigned a reference to where "xyz" is stored in the intern pool, this won't affect 'b' which will still refer to "abc".
Sharad Gupta14y ago
I want to know in heap string a reference to memory of abc and b is also reference the memory of abc but when i assign a new value to a then what happened, a 's value override last value or it takes new memory space for a new value.
Shivanand Arur14y ago
Since string us a reference type, all the data will be stored on Heap... I hope this is what you wanted to know.... Let me know id U still have any doubt....