[#9] – Pointers – Questions

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Pointers are one of the most powerful features available in C++. The use of pointers offers a great degree of flexibility for manipulating data in programs and making programs quicker and memory efficient.

Index:

Most of the learners feel that understanding pointer is a very daunting task, but it is not so. Although programming can be done without the use of pointers but in some situations, pointers show its real power such as

Management of objects allocated memory dyanamically
Passing arrays, strings to functions more efficiently
To pass function arguments that will be changed by the function
To return more than one value from the function
To pass address of structures or objects instead of entire object to functions
Creation of linked data structures such as Linked Lists, Trees, Graphs etc
Optimize the program to execute faster or use less memory.

Key Points To Remember –

A pointer is a variable that contains the address of another variables. Pointer variables are also known as address variables as they always store address of some other variable.
The address of the variable can be obtained by preceding the name of the variable with address of operator(&).
Deference operator(*) returns the value of the variable pointed to by the pointer variable.
Pointer to a pointer means that a variable can be declared which can store the address of a pointer variable. They offer a great degree of flexibility for handling arrays, passing pointer variables to functions and passing command line arguments.
When an integer value is added to a pointer variable, the pointer variable is not incremented by that integer value instead it is incremented by address stored currently in pointer variable plus increment value multiplied by sizeof type to which pointer variable points to.
The new operator is used to allocate memory at runtime and returns a pointer to that memory location.
The delete operator is used to deallocate the memory allocated using new operator.

Viva Voce Questions –

Here are commonly asked questions with answers:

Can we write a[i] as i[a] ?
- Yes,since a[i] can be accessed using pointer notation as *(a+i) which is equivalent to *(i+a). Thus in turn equal to i[a].
What is the difference between ++s→a and s++→a ?
- The first one increments the contents of data member a and not s structure variable. However, in the second statement, structure variable s is incremented after accessing data member a.
What is dangling reference ?
- It refers to a situation when a portion of memory referred through pointer is released (in the free pool) but pointer still point to it. It happens when memory is not released explicitly.
What is the difference between int *const ptr=i; and const int * const ptr=i; ?
- The first one defines a constant pointer to integer i and you cannot modify the pointer. But in the second one. you cannot modify the pointer as well as integer to which integer is pointing.
What is memory leak ?
- It is a block of dynamically allocated memory that we no longer have a pointer pointing to it and thus we cannot return it to the program for later reuse. It is usually encountered when we forget to delete dynamically allocated array.
When will you encounter null pointer assignment error ?
- When you try to perform read or write operation using null pointer.
What is the difference between pointer to arrays and array of pointers ?
- Pointer to array refers to using a single pointer to access elements of an array whereas array of pointers refers to collection of pointer variables that hold the address of different array elements.
What does the following declaration mean:
type (*fp)() and type *fp()
- In first case, fp is a pointer function that accepts no arguments and return type. In the second case, fp is a function that accepts no arguments and returns a pointer to type.
What is null pointer ?
- C++ defines a special value called null pointer for each pointer type. It is used to compare a pointer to any object or function. The internal representation of null pointer for different data type may be different.