Monday 19 April 2021

Pointer and Reference Types | PPL | Sebesta | Data Types in Programming Language

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9. Pointer and reference Type



              A pointer type is one in which the variables have a range of values that consists of memory addresses and a special value, nil.


              A pointer can be used to access a location in an area where storage is dynamically allocated called a heap.


              Variables that are dynamically allocated from the heap are called heap-dynamic variables.



Dangling Pointer

              A dangling pointer, or dangling reference, is a pointer that contains the address of a heap-dynamic variable that has been deallocated.



Example from C++ Language:


int * ptr1;

int * ptr2 = new int[100];

ptr1 = ptr2;

delete [] ptr2;


              Here,  ptr1 and  ptr2, both will be dangling pointers.


              Java class instances are implicitly deallocated (there is no explicit deallocation operator), there cannot be dangling references in Java.



Reference Type:

              A reference type variable is similar to a pointer, with one important and fundamental difference: A pointer refers to an address in memory, while a reference refers to an object or a value in memory.




int a = 0;

int &b = a;

b = 100;


              In this code segment, variables a and b are aliases. b is reference to a.

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