Pointer Operators

The address operator (&) is a unary operator that returns the memory address of its operand. For example, assuming the declarations

int y = 5; // declare variable y
int *yPtr; // declare pointer variable yPtr

the statement

yPtr = &y; // assign address of y to yPtr

assigns the address of the variable y to pointer variable yPtr. Then variable yPtr is said to "point to" y. Now, yPtr indirectly references variable y's value. Note that the use of the & in the preceding assignment statement is not the same as the use of the & in a reference variable declaration, which is always preceded by a data-type name.

Figure 8.2 shows a schematic representation of memory after the preceding assignment. The "pointing relationship" is indicated by drawing an arrow from the box that represents the pointer yPtr in memory to the box that represents the variable y in memory.

Figure 8.2. Graphical representation of a pointer pointing to a variable in memory.

Figure 8.3 shows another representation of the pointer in memory, assuming that integer variable y is stored at memory location 600000 and that pointer variable yPtr is stored at memory location 500000. The operand of the address operator must be an lvalue (i.e., something to which a value can be assigned, such as a variable name or a reference); the address operator cannot be applied to constants or to expressions that do not result in references.

Figure 8.3. Representation of y and yPtr in memory.

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The * operator, commonly referred to as the indirection operator or dereferencing operator, returns a synonym (i.e., an alias or a nickname) for the object to which its pointer operand points. For example (referring again to Fig. 8.2), the statement

cout << *yPtr << endl;

prints the value of variable y, namely, 5, just as the statement

cout << y << endl;

would. Using * in this manner is called dereferencing a pointer. Note that a dereferenced pointer may also be used on the left side of an assignment statement, as in

*yPtr = 9;

which would assign 9 to y in Fig. 8.3. The dereferenced pointer may also be used to receive an input value as in

cin >> *yPtr;

which places the input value in y. The dereferenced pointer is an lvalue.

Common Programming Error 8.2

Dereferencing a pointer that has not been properly initialized or that has not been assigned to point to a specific location in memory could cause a fatal execution-time error, or it could accidentally modify important data and allow the program to run to completion, possibly with incorrect results.

Common Programming Error 8.3

An attempt to dereference a variable that is not a pointer is a compilation error.

Common Programming Error 8.4

Dereferencing a null pointer is normally a fatal execution-time error.

The program in Fig. 8.4 demonstrates the & and * pointer operators. Memory locations are output by << in this example as hexadecimal (i.e., base-16) integers. (See Appendix D, Number Systems, for more information on hexadecimal integers.) Note that the hexadecimal memory addresses output by this program are compiler and operating-system dependent, so you may get different results when you run the program.

Figure 8.4. Pointer operators & and *.

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 1 // Fig. 8.4: fig08_04.cpp
 2 // Using the & and * operators.
 3 #include 
 4 using std::cout;
 5 using std::endl;
 7 int main()
 8 {
 9 int a; // a is an integer
10 int *aPtr; // aPtr is an int * -- pointer to an integer
12 a = 7; // assigned 7 to a
13 aPtr = &a; // assign the address of a to aPtr
15 cout << "The address of a is " << &a
16 << "
The value of aPtr is " << aPtr;
17 cout << "

The value of a is " << a
18 << "
The value of *aPtr is " << *aPtr;
19 cout << "

Showing that * and & are inverses of "
20 << "each other.
&*aPtr = " << &*aPtr
21 << "
*&aPtr = " << *&aPtr << endl;
22 return 0; // indicates successful termination
23 } // end main
 The address of a is 0012F580
 The value of aPtr is 0012F580

 The value of a is 7
 The value of *aPtr is 7

 Showing that * and & are inverses of each other.
 &*aPtr = 0012F580
 *&aPtr = 0012F580

Portability Tip 8.1

The format in which a pointer is output is compiler dependent. Some systems output pointer values as hexadecimal integers, while others use decimal integers.

Notice that the address of a (line 15) and the value of aPtr (line 16) are identical in the output, confirming that the address of a is indeed assigned to the pointer variable aPtr. The & and * operators are inverses of one anotherwhen they are both applied consecutively to aPtr in either order, they "cancel one another out" and the same result (the value in aPtr) is printed.

Figure 8.5 lists the precedence and associativity of the operators introduced to this point. Note that the address operator (&) and the dereferencing operator (*) are unary operators on the third level of precedence in the chart.

Figure 8.5. Operator precedence and associativity.







left to right




static_cast<type>( operand )

left to right

unary (postfix)








right to left

unary (prefix)





left to right





left to right





left to right







left to right





left to right




left to right

logical AND



left to right

logical OR



right to left









right to left




left to right


Introduction to Computers, the Internet and World Wide Web

Introduction to C++ Programming

Introduction to Classes and Objects

Control Statements: Part 1

Control Statements: Part 2

Functions and an Introduction to Recursion

Arrays and Vectors

Pointers and Pointer-Based Strings

Classes: A Deeper Look, Part 1

Classes: A Deeper Look, Part 2

Operator Overloading; String and Array Objects

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism


Stream Input/Output

Exception Handling

File Processing

Class string and String Stream Processing

Web Programming

Searching and Sorting

Data Structures

Bits, Characters, C-Strings and structs

Standard Template Library (STL)

Other Topics

Appendix A. Operator Precedence and Associativity Chart

Appendix B. ASCII Character Set

Appendix C. Fundamental Types

Appendix D. Number Systems

Appendix E. C Legacy Code Topics

Appendix F. Preprocessor

Appendix G. ATM Case Study Code

Appendix H. UML 2: Additional Diagram Types

Appendix I. C++ Internet and Web Resources

Appendix J. Introduction to XHTML

Appendix K. XHTML Special Characters

Appendix L. Using the Visual Studio .NET Debugger

Appendix M. Using the GNU C++ Debugger


C++ How to Program
C++ How to Program (5th Edition)
ISBN: 0131857576
EAN: 2147483647
Year: 2004
Pages: 627

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