Pointers

Question 1

Are pointer variables passed by value or by reference to functions?

Answer 1

Pointer variables are passed by value to functions

Question 2

What is the difference between & and *?

Answer 2

&: Given a variable of type X, it gives X* ( the appropriate pointer ) the address of the variable

*: Given a variable of type X*, show what x points to

Question 3

What is a pointer?

Answer 3

A pointer is a variable that contains the address of another variable

Question 4

what does the array variable point to?

Answer 4

The array variable points to the first element in the array

Question 5

Can you use the square brackets [] with a pointer to an array

Answer 5

yes, the [] can be used interchangeably with an array as well as a pointer

Array indexing and pointer arithemtic works identical

Question 6

What is the size of a pointer?

Answer 6

The size of a pointer is the width of the processor

sizeof(int*) = 4 bytes in a 32 bit system

sizeof(int*) = 8 in a 64 bit system

Question 7

What is the difference between an array and a pointer to an array?

or

How to distinguish between these 2?

Answer 7

The size of the array computer using the sizeof operator will be the sum of the sizes of all the elements inside the array but the sizeof the pointer will always be the width of the system.

Also, variable assignments are invalid in the case of arrays.

int array[100];

array = (some other variable) // invalid because there are not variables associated with an array

Question 8

In what chunks do pointers get incremented?

Answer 8

The pointer gets incremented in chunks of the size of the type of the pointer.

So, if the pointer is an int*, then adding 1 to the pointer will add sizeof(int) usually 4, to the address.

Question 10

What are dangling pointers?

Answer 10

Dangling pointers are pointers that point to variable which was created on the stack which no longer is present in that memory location in the stack.

Question 11

Why is the string.h library important?

Answer 11

it contains functions for working with strings.

Question 12

What is the prototype for strcpy and what should you watch out for?

Answer 12

The prototype for strcpy is char* strcpy ( char* str1, const char* str2 );

You need to make sure that str1 has enough memory to store str2

Question 13

Prototype and use of gets function in string.h library?

Answer 13

Prototype: char* gets( char* s);

reads a input into s until an EOF or \n is encountered

It could overflow the character array s.

Question 14

Prototype and use of puts function in string.h library?

Answer 14

Prototype: puts int puts( const char* s)

Don’t know what it returns lol

it prints out the string s and also appends a newline.

Question 15

Prototype and use of sprintf() function in string.h library?

Answer 15

Prototype:

int printf( char* s, const char* format, ….)

Works like the printf function but instead of outputting the string to the console, the string is stored written into a variable s.

Question 16

Prototype and use of sscanf function in string.h library?

Answer 16

Prototype: int sscanf(char* s, char* format, …..)

It works like scanf, but instead of reading the input from the stdin, it reads in the input from a variable and the programmer has to specify the input specifiers in the format string and the input variables ( how many ever there are ) after that.

Question 17

How does the strcmp function work?

Answer 17

The strcmp function takes in 2 strings and returns

• 0 if they are equal
• > 0 if the first one is greater than the second one
• < 0 if the first one is smaller than the second one

Question 18

What is the void pointer used for?

Answer 18

The void pointer is a polymorphic pointer that can point to any data of any type.

Void* cannot be dereferenced and it cannot be used for pointer arithmetic

It can only be used to point to data and not to functions

Question 19

What is the null pointer?

Answer 19

Null is a generic pointer that doesn’t point to anything and is represented as (void*)0

it cannot be dereferenced

It is possible to turn a null pointer into any type of pointer.

Question 20

How do you access a member for a struct given a pointer s to a struct? 2 ways

Answer 20

• (*s).m
• s -> m

Question 21

What is a polymorphic pointer?

Answer 21

A polymorphic pointer is a pointer that can point to any type.

Question 22

1. Pointer can be cast from one type to any type
2. Implicit pointer casting leads to a warning
3. You can pass function pointers to other functions and have them execute the function specified by the pointers.

Question 23

What are pointers to functions used for?

Answer 23

They are used to refer to functions that have been already created and can be used to pass around functions and assign them to variables.

Question 24

How do you create function pointers?

Answer 24

<return> *(<name>)(<arguments>) = function name;</arguments></name></return>

int addNumbers(int a, int b) { return a + b;}

int (*fun)(int a, int b) = addNumbers;

Question 25

How do you typedef a function pointer?

Answer 25

in order to define a type of function, use the following syntax

typedef <return> (*<name>)(argument list without the names of the variables)</name></return>

typedef int(*fun_ptr) (int, int); creates a type fun_ptr that can point to a function which takes in 2 integer arguments and returns an integer.

Question 27

What are asserts and how could it be used?

Answer 27

They are functions that can be used for internal checks within the program

It should be used to check for bugs within the code and not to check the user input.

assert(x) aborts the program if x is false.

Question 28

How would you disable assert?

Answer 28

define NDEBUG

Assert can be disabled by using