Pointers in C Programming

POINTERS Presented by Er. Jasleen Kaur Assistant Professor Applied Science(CSE) Chandigarh University Gharuan (Mohali).

Pointer • A variable that holds a memory address. • This address is the location of another object in the memory. • Pointer as an address indicates where to find an object. Not all pointers actually contain an address example NULL pointer. Value of NULL pointer is 0. 10/19/2015

• Pointer can have three kinds of content in it 1) The address of an object, which can be dereferenced. 2) A NULL pointer. 3) Invalid content, which does not point to an object. (If p does not hold a valid value, it can crash the program) • If p is a pointer to integer, then – Int *p

It is possible in some environments to have multiple pointer values with different representations that point to same location in memory. But make sure if the memory is deleted using delete or if original variable goes out of scope.

Declaring pointer Data-type *name; * is a unary operator, also called as indirection operator. Data-type is the type of object which the pointer is pointing. Any type of pointer can point to anywhere in the memory. * is used to declare a pointer and also to dereference a pointer.

When you write int *, compiler assumes that any address that it holds points to an integer type.  m= &count; it means memory address of count variable is stored into m. & is unary operator that returns the memory address. i.e. & (orally called as ampersand) is returning the address.  so it means m receives the address of count.

Suppose, count uses memory Address 2000 to store its value 100. so, m=&count means m has 2000 address. q= *m it returns the value at address m. value at address 2000 is 100. so, q will return value 100. i.e. q receives the value at address m. count=1002000

Address-of operator(&) • It is used to reference the memory address of a variable. • When we declare a variable, 3 things happen – Computer memory is set aside for variable – Variable name is linked to that location in memory – Value of variable is placed into the memory that was set aside.

Int *ptr; declaring variable ptr which holds the value at address of int type  int val =1; assigning int the literal value of 1  ptr=&val; dereference and get value at address stored in ptr int deref =*ptr printf(“%dn”, deref); Output will be 1

Pointer Conversions • One type of pointer can be converted to another type of pointer. • int main() { double x=100.1, y; int *p; p= (int *) &x; //explicit type conversion y= *p; }

Generic Pointer void * pointer is called as generic pointer. Can’t convert void *pointer to another pointer and vice-versa. void *pointer can be assigned to any other type of pointer. void * is used to specify a pointer whose base type is unknown. It is capable of receiving any type of pointer argument without reporting any type of mismatch.

Pointer Arithmetic • There are only two arithmetic operations that can be used on pointers – Addition – Subtraction • To understand this concept, lets p1 be an integer pointer with value 2000 address. – int is of 2 bytes – After expression p1++; – P1 contains address 2002 not 2001.

• Each time p1 is incremented, it will point to next integer. • The same is true for decrement. – for p1--; – Causes value of p1 to be 1998. • Each time a pointer is incremented, it points to the memory location of the next element of its base type. • If decremented, then it points to previous element location. • P1=p1+12; makes p1 points to 12th element of p1 type.

Arithmetic Rules • You cannot multiply or divide pointers. • You cannot add or subtract two pointers. • You cannot apply bitwise operators to them. • You cannot add or subtract type float or double to or from pointers.

Pointer Comparison • You can compare two pointers in a relational expression, example: if(p<q) printf(“p points to lower memory than q n”); • Pointer comparison are useful only when two pointers point to a common object such as an array.

Benefits of pointer • Pointers are used in situations when passing actual values is difficult or not desired. • To return more than one value from a function. • They increase the execution speed. • The pointer are more efficient in handling the data types . • Pointers reduce the length and complexity of a program.

• The use of a pointer array to character string results in saving of data. • To allocate memory and access it( Dynamic memory Allocation). • Implementing linked lists, trees graphs and many other data structure.

How to get address of a function /*A program to get address of a function */ #include<stdio.h> void main() { void show(); /* usual way of invoking a function */ printf(“ The address of show function is=%u”, show); } void show() { printf(“ welcome to HPES!!”) }

Uses of pointer to function • Pointers are certainly awkward and off-putting and thus this feature of pointer is used for invoking a function • There are several possible uses : (a) In writing memory resident program. (b) In writing viruses, or vaccines to remove the viruses. (c) In developing COM/DCOM component (d) In VC++ programming to connect events to function calls.

Pointers in C Programming

In this document

More Related Content

What's hot

Similar to Pointers in C Programming

More from Jasleen Kaur (Chandigarh University)

Recently uploaded

Pointers in C Programming