C++ pointers are easy and fun to learn. Some C++ tasks are performed more easily with pointers, and other C++ tasks, such as dynamic memory allocation, cannot be performed without them.
As you know every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator which denotes an address in memory. Consider the following which will print the address of the variables defined:
#include <iostream> using namespace std; int main () { int var1; char var2[10]; cout << "Address of var1 variable: "; cout << &var1 << endl; cout << "Address of var2 variable: "; cout << &var2 << endl; return 0; }
When the above code is compiled and executed, it produces result something as follows:
Address of var1 variable: 0xbfebd5c0 Address of var2 variable: 0xbfebd5b6
What Are Pointers?
A pointer is a variable whose value is the address of another variable. Like any variable or constant, you must declare a pointer before you can work with it. The general form of a pointer variable declaration is:
type *var-name;
Here, type is the pointer's base type; it must be a valid C++ type and var-name is the name of the pointer variable. The asterisk you used to declare a pointer is the same asterisk that you use for multiplication. However, in this statement the asterisk is being used to designate a variable as a pointer. Following are the valid pointer declaration:
int *ip; // pointer to an integer double *dp; // pointer to a double float *fp; // pointer to a float char *ch // pointer to character
The actual data type of the value of all pointers, whether integer, float, character, or otherwise, is the same, a long hexadecimal number that represents a memory address. The only difference between pointers of different data types is the data type of the variable or constant that the pointer points to.
Using Pointers in C++:
There are few important operations, which we will do with the pointers very frequently. (a) we define a pointer variables (b) assign the address of a variable to a pointer and (c) finally access the value at the address available in the pointer variable. This is done by using unary operator * that returns the value of the variable located at the address specified by its operand. Following example makes use of these operations:
#include <iostream> using namespace std; int main () { int var = 20; // actual variable declaration. int *ip; // pointer variable ip = &var; // store address of var in pointer variable cout << "Value of var variable: "; cout << var << endl; // print the address stored in ip pointer variable cout << "Address stored in ip variable: "; cout << ip << endl; // access the value at the address available in pointer cout << "Value of *ip variable: "; cout << *ip << endl; return 0; }
When the above code is compiled and executed, it produces result something as follows:
Value of var variable: 20 Address stored in ip variable: 0xbfc601ac Value of *ip variable: 20
C++ Pointers in Detail:
Pointers have many but easy concepts and they are very important to C++ programming. There are following few important pointer concepts which should be clear to a C++ programmer:
| Concept | Description |
|---|---|
C++ Null Pointers
| C++ supports null pointer, which is a constant with a value of zero defined in several standard libraries. |
C++ pointer arithmetic
| There are four arithmetic operators that can be used on pointers: ++, --, +, - |
C++ pointers vs arrays
| There is a close relationship between pointers and arrays. Let us check how? |
C++ array of pointers
| You can define arrays to hold a number of pointers. |
C++ pointer to pointer
| C++ allows you to have pointer on a pointer and so on. |
Passing pointers to functions
| Passing an argument by reference or by address both enable the passed argument to be changed in the calling function by the called function. |
Return pointer from functions
| C++ allows a function to return a pointer to local variable, static variable and dynamically allocated memory as well. |
