C++ Pointers
Creating Pointers
You learned from the previous chapter, that we can get the memory
address of a variable by using the &
operator:
Example
string food = "Pizza";
// A food variable of type string
cout <<
food; // Outputs the value of food (Pizza)
cout << &food; // Outputs the memory address of food (0x6dfed4)
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A pointer however, is a variable that stores the memory address as its value.
A pointer variable points to a data type (like int or string) of the same
type, and is created with the * operator. The address of the variable you're working with is assigned to the pointer:
Example
string food = "Pizza"; // A food variable
of type string
string* ptr =
&food; // A pointer variable, with the name
ptr, that stores the
address of food
// Output the value of food (Pizza)
cout << food << "\n";
// Output
the memory address of food (0x6dfed4)
cout << &food << "\n";
//
Output the memory address of food with the pointer (0x6dfed4)
cout <<
ptr << "\n";
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Example explained
Create a pointer variable with the name ptr, that points to a string variable, by using the
asterisk sign
* (string* ptr).
Note that the type of the pointer has to match the type of the variable you're
working with.
Use the & operator to store the memory address of the
variable called food, and assign it to the pointer.
Now, ptr holds the value of food's memory address.
Tip: There are three ways to declare pointer variables, but the first way is preferred:
string* mystring; // Preferred
string *mystring;
string * mystring;
Get Memory Address and Value
In the example above, we used the pointer variable to get the memory address of a variable
(used together with the & reference operator). However, you can also
use the pointer to get the value of the variable, by using the * operator
(the dereference operator):
Example
string food = "Pizza"; // Variable declaration
string* ptr =
&food; // Pointer declaration
//
Reference: Output the memory address of food with the pointer (0x6dfed4)
cout <<
ptr << "\n";
//
Dereference: Output the value of food with the pointer (Pizza)
cout <<
*ptr << "\n";
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Note that the * sign can be confusing here, as it does two different things
in our code:
- When used in declaration (string* ptr), it creates a pointer variable.
- When not used in declaration, it act as a dereference operator.
Modify the Pointer Value
You can also change the pointer's value. But note that this will also change the value of the original variable:
Example
string food = "Pizza";
string* ptr = &food;
// Output the value
of food (Pizza)
cout << food << "\n";
// Output the memory address
of food (0x6dfed4)
cout << &food << "\n";
// Access the memory
address of food and output its value (Pizza)
cout << *ptr << "\n";
// Change the value of the pointer
*ptr = "Hamburger";
//
Output the new value of the pointer (Hamburger)
cout << *ptr << "\n";
//
Output the new value of the food variable (Hamburger)
cout << food << "\n";
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