A pointer is a variable that stores the address of another variable. Unlike other variables that hold values of a certain type, pointer holds the address of a variable. For example, an integer variable holds (or you can say stores) an integer value, however an integer pointer holds the address of a integer variable. In this post, we will discuss pointers in C programming.
Before we discuss about pointers in C, lets take to understand what do we mean by the address of a variable.
C Pointers – Operators that are used with Pointers
Lets discuss the operators & and * that are used with Pointers in C.
“Address of”(&) Operator
We have already seen in the first example that we can display the address of a variable using ampersand sign. I have used &num to access the address of variable num. The & operator is also known as “Address of” Operator.
printf("Address of var is: %p", &num);
Point to note: %p is a format specifier which is used for displaying the address in hex format.
Now that you know how to get the address of a variable but how to store that address in some other variable? That’s where pointers comes into picture. As mentioned in the beginning of this guide, pointers in C programming are used for holding the address of another variables.
Pointer is just like another variable, the main difference is that it stores address of another variable rather than a value.
“Value at Address”(*) Operator
The * Operator is also known as Value at address operator.
How to declare a pointer?
int *p1 /*Pointer to an integer variable*/ double *p2 /*Pointer to a variable of data type double*/ char *p3 /*Pointer to a character variable*/ float *p4 /*pointer to a float variable*/
The above are the few examples of pointer declarations. If you need a pointer to store the address of integer variable then the data type of the pointer should be int. Same case is with the other data types.
By using * operator we can access the value of a variable through a pointer.
double a = 10; double *p; p = &a;
*p would give us the value of the variable a. The following statement would display 10 as output.
Similarly if we assign a value to *pointer like this:
*p = 200;
It would change the value of variable a. The statement above will change the value of a from 10 to 200.
More points on Pointers
1) Pointer to Pointer – A pointer can point to another pointer (which means it can store the address of another pointer), such pointers are known as double pointer OR pointer to pointer.
2) Passing pointers to function – Pointers can also be passed as an argument to a function, using this feature a function can be called by reference as well as an array can be passed to a function while calling.
3) Function pointers – A function pointer is just like another pointer, it is used for storing the address of a function. Function pointer can also be used for calling a function in C program.