(C++ programming Example for Beginners)
C++ Pointers
In this tutorial, we will learn about pointers in C++ and their working with the help of examples.
In C++, pointers are variables that store the memory addresses of other variables.
Address in C++
If we have a variable var in our program, &var will give us its address in the memory. For example,
Example 1: Printing Variable Addresses in C++
#include <iostream>
using namespace std;
int main(){
// declare variables
int var1 = 3;
int var2 = 24;
int var3 = 17;
// print address of var1
cout << "Address of var1: "<< &var1 << endl;
// print address of var2
cout << "Address of var2: " << &var2 << endl;
// print address of var3
cout << "Address of var3: " << &var3 << endl;
}
Output
Address of var1: 0x7fff5fbff8ac Address of var2: 0x7fff5fbff8a8 Address of var3: 0x7fff5fbff8a4
Here, 0x
at the beginning represents the address is in the hexadecimal form.
Notice that the first address differs from the second by 4 bytes and the second address differs from the third by 4 bytes.
This is because the size of an int
variable is 4 bytes in a 64-bit system.
Note: You may not get the same results when you run the program.
C++ Pointers
As mentioned above, pointers are used to store addresses rather than values.
Here is how we can declare pointers.
int *pointVar;
Here, we have declared a pointer pointVar of the int
type.
We can also declare pointers in the following way.
int* pointVar; // preferred syntax
Let’s take another example of declaring pointers.
int* pointVar, p;
Here, we have declared a pointer pointVar and a normal variable p.
Note: The *
operator is used after the data type to declare pointers.
Assigning Addresses to Pointers
Here is how we can assign addresses to pointers:
int* pointVar, var;
var = 5;
// assign address of var to pointVar pointer
pointVar = &var;
Here, 5
is assigned to the variable var. And, the address of var is assigned to the pointVar pointer with the code pointVar = &var
.
Get the Value from the Address Using Pointers
To get the value pointed by a pointer, we use the *
operator. For example:
int* pointVar, var;
var = 5;
// assign address of var to pointVar
pointVar = &var;
// access value pointed by pointVar
cout << *pointVar << endl; // Output: 5
In the above code, the address of var is assigned to pointVar. We have used the *pointVar
to get the value stored in that address.
When *
is used with pointers, it’s called the dereference operator. It operates on a pointer and gives the value pointed by the address stored in the pointer. That is, *pointVar = var
.
Note: In C++, pointVar and *pointVar is completely different. We cannot do something like *pointVar = &var;
Example 2: Working of C++ Pointers
#include <iostream>
using namespace std;
int main(){
int var = 5;
// declare pointer variable
int* pointVar;
// store address of var
pointVar = &var;
// print value of var
cout << "var = " << var << endl;
// print address of var
cout << "Address of var (&var) = " << &var << endl
<< endl;
// print pointer pointVar
cout << "pointVar = " << pointVar << endl;
// print the content of the address pointVar points to
cout << "Content of the address pointed to by pointVar (*pointVar) = " << *pointVar << endl;
return 0;
}
Output
var = 5 Address of var (&var) = 0x61ff08 pointVar = 0x61ff08 Content of the address pointed to by pointVar (*pointVar) = 5
Changing Value Pointed by Pointers
If pointVar points to the address of var, we can change the value of var by using *pointVar.
For example,
int var = 5;
int* pointVar;
// assign address of var
pointVar = &var;
// change value at address pointVar
*pointVar = 1;
cout << var << endl; // Output: 1
Here, pointVar and &var
have the same address, the value of var will also be changed when *pointVar is changed.
Example 3: Changing Value Pointed by Pointers
#include <iostream>
using namespace std;
int main(){
int var = 5;
int* pointVar;
// store address of var
pointVar = &var;
// print var
cout << "var = " << var << endl;
// print *pointVar
cout << "*pointVar = " << *pointVar << endl
<< endl;
cout << "Changing value of var to 7:" << endl;
// change value of var to 7
var = 7;
// print var
cout << "var = " << var << endl;
// print *pointVar
cout << "*pointVar = " << *pointVar << endl
<< endl;
cout << "Changing value of *pointVar to 16:" << endl;
// change value of var to 16
*pointVar = 16;
// print var
cout << "var = " << var << endl;
// print *pointVar
cout << "*pointVar = " << *pointVar << endl;
return 0;
}
Output
var = 5 *pointVar = 5 Changing value of var to 7: var = 7 *pointVar = 7 Changing value of *pointVar to 16: var = 16 *pointVar = 16
Common mistakes when working with pointers
Suppose, we want a pointer varPoint to point to the address of var. Then,
int var, *varPoint;
// Wrong!
// varPoint is an address but var is not
varPoint = var;
// Wrong!
// &var is an address
// *varPoint is the value stored in &var
*varPoint = &var;
// Correct!
// varPoint is an address and so is &var
varPoint = &var;
// Correct!
// both *varPoint and var are values
*varPoint = var;
C++ for Beginners: C++ Pointers
Disclaimer: The information and code presented within this recipe/tutorial is only for educational and coaching purposes for beginners and developers. Anyone can practice and apply the recipe/tutorial presented here, but the reader is taking full responsibility for his/her actions. The author (content curator) of this recipe (code / program) has made every effort to ensure the accuracy of the information was correct at time of publication. The author (content curator) does not assume and hereby disclaims any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from accident, negligence, or any other cause. The information presented here could also be found in public knowledge domains.