dangling pointer

Question

operations :
(i) Pointer p1 is set to point at a new heap-dynamic variable.
(ii) Pointer p2 is assigned p1’s value.
(iii) The heap dynamic variable pointed to by p1 is explicitly de-allocated, but p2 is not changed by the operation.

This situation leads to which of the following :

(A) p1 becomes a dangling pointer
(B) p2 becomes a dangling pointer
(C) Both p1 and p2 are now dangling pointers
(D) Neither p1 nor p2 is now a dangling pointer

Comments

what is the meaning?

p2 is not changed by the operation

Answer 1

Dangling pointers arise when an object is deleted or deallocated, without modifying the value of the pointer, so that the pointer still points to the memory location of the de-allocated memory.

Since P2 is pointing the memory location that has been de-allocated .So we can say P2 becomes dangling pointer.

Comments

what about pointer p1 what it is called

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I think p1 should also be called dangling pointer.

what do you say @ManojK  ??

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Why p1 is not dp

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P1 can be changed by other operation so we can,t say p1 is dangling but if the de-allocation operation does not change p1 then both p1 and p2 will be dangling.

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@Sanjay @manojk please clear my doubt 

As they said in first statement "Pointer p1 is set to point at a new heap-dynamic variable" Here i have assumed D as new heap-dynamic variable which has a memory address as 100 (just an assumption).

Second statement says  "Pointer p2 is assigned p1’s value." .I did the same thing P2 ia holding the value of P1 (it is holding the address(value) because it is a pointer .)

statements 3 says "The heap dynamic variable pointed to by p1 is explicitly de-allocated" . then p1 is not going to point anything now But a/c to statement " p2 is not changed by the operation." means it is still pointing to something .

Now my question is How come a pointer(P2) which is pointing to something becomes dangling pointer. .Here P1 must be a dangling pointer....

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@shekhar sir,why are u making p2 a pointer of p1?

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@kapil second statements says this "(ii) Pointer p2 is assigned p1’s value."

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This means whatever p1 has been assigned or pointing to ,, same p2 should do....

they are not saying p2 points to p1..

they are actually saying, whatever be the contents of p1, p2 should also get that... and yeah memory addresses of both pointers will be different, but both pointing to same variBle...

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@okay kapil if this is the case then both p1 and p2 will be pointing to the same address location generated by new heap-dynamic variable then why only p2 is dangling pointer..  if the location de-allocated then it should effect poth p1 and p2 because both are pointing to the same location ..and in that case both p1 and p2 should be dangling pointer..

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sir,

when we delete last element of linked list, then we have to traverse from first node to last and then delete...

but , after this operation , we set last second node to NULL., i.e we are explicitly making it null ...

and if we dont set it to NULL by thinking that it will do this automatically , then no it will not , it will be a dangling pointer now...

The heap dynamic variable pointed to by p1 is explicitly de-allocated, but p2 is not changed by the operation   

this statement says p1 is explicitly deallocated,, we can do that by making p1 = NULL, which means now p1 is not pointing to anything.

but p2 is not changed by the operation, which means no action has been done and it is still pointing to that location which has been deallocated,,, hence, it is a dangling pointer...

after deallo. , we changed p1 but we didnt change p2...

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@kapil thanks I understood now the difference .