Data Structures Using C++1 Chapter 3 Pointers Dr. Liu.
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Transcript of Data Structures Using C++1 Chapter 3 Pointers Dr. Liu.
Data Structures Using C++ 1
Chapter 3
Pointers
Dr. Liu
Data Structures Using C++ 2
Chapter Objectives
• Learn about the pointer data type and pointer variables
• Explore how to declare and manipulate the pointer variables
• Learn about the address of operator and dereferencing operator
• Discover dynamic variables• Examine how to use the new and delete operators
to manipulate dynamic variables
Data Structures Using C++ 3
Chapter Objectives
• Learn about pointer arithmetic• Discover dynamic arrays• Become aware of the shallow and deep
copies of data• Discover the peculiarities of classes with
pointer data members• Explore how dynamic arrays are used to
process lists
Data Structures Using C++ 4
What are pointers ?
• Variables that store memory address
•How to De-reference pointers
•How to do Pointer assignment
•How to use address-of operator
Data Structures Using C++ 5
What are pointers ?
5
3
8
1000
a
b
c
p
1000
1004
1008
1012
Address
int *p; int a = 5;p = &a; what is *p now ?;*p = *p + b; int c = *p;
Data Structures Using C++ 6
Pointer Data Types and Pointer Variables
• Pointer variable: variable whose content is a memory address
• Syntax to declare pointer variable:dataType *identifier; e.g. int *p;
• Address of operator: Ampersand, &, e.g. &a
• Dereferencing operator: Asterisk, *
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Pointers
• Statements:
int *p;
int num;
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Pointers
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Pointers
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Pointers
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Pointers
• Summary of preceding diagrams– &p, p, and *p all have different meanings– &p means the address of p– p means the content of p– *p means the content pointed to by p, that is
pointed to by the content of memory location
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Pointers
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Pointersx = 50;
p = &x;
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Pointers
*p = 38;
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Example 1
• // This program passes the address of a variable to a
• // function, which triples the value pointed to.
• Pointer example demo 1
• void triple_it(int *n);
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Example 2
• // This program sorts an array from hightest member
• // down to lowest, in that order.
• Pointer example demo 2.
• void swap(int *p1, int *p2)
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Example 3• void zero_out_array(int *arr, int n); void
zero_out_array(int *p, int n) {
• while (n-- > 0) { // Do n times:
• *p = 0; // Assign 0 to element // pointed to by p.
• p++; // Point to next element.
• }
• }
Data Structures Using C++ 18
Classes, structs, and Pointer Variables
The syntax for accessing a class (struct) member using the operator -> is
pointerVariableName->classMemberName
Therefore, the statement
(*studentPtr).gpa = 3.9;
is equivalent to the statement
studentPtr->gpa = 3.9;
Data Structures Using C++ 19
Classes, structs, and Pointer Variables
Data Structures Using C++ 20
Classes, structs, and Pointer Variables
Data Structures Using C++ 21
Syntax to use operator new
new dataType; //to allocate a single variable
new dataType[intExp]; //to allocate an array of variables
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Syntax to use operator delete
delete pointer; //to destroy a single dynamic variable
delete [] pointer; //to destroy a dynamically created array
Data Structures Using C++ 23
Operations on pointer variables
• Assignment operations
• Relational operations
• Limited arithmetic operations
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Functions and Pointers
void example(int* &p, double *q)
{
.
.
.
}
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Functions and Pointersvoid example(int* &p, double *q)
{
.
.
.
}
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Pointers and Function Return Pointers
int* testExp(...)
{
.
.
.
}
is a pointer of the type int.
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#include <stdio.h>
#define PRINTEM printf("%3d%5d%5d%5d%5d%5d\n", line++, num, x[0],x[1],x[2], ptr-x)
int main() {
static int x[] = {5,10,15}, lim =99;
int *ptr = x, num = 0;
int line = 0;
printf("LINE num x[0] x[1] x[2] ptr-x \n");
PRINTEM;
printf("\n\n");
num = *ptr; PRINTEM;
num = *++ptr; PRINTEM;
num = *ptr++; PRINTEM;
num = ++*ptr; PRINTEM;
num = (*ptr)++; PRINTEM;
num = ++(*ptr); PRINTEM;
num = *ptr + 1; PRINTEM;
num = *(ptr + 1); PRINTEM;
return 0;
}
Data Structures Using C++ 28
Shallow Versus Deep Copy and Pointers
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Shallow Versus Deep Copy and Pointers
Data Structures Using C++ 30
Shallow Versus Deep Copy and Pointers
second = new int[10];
for(int j = 0; j < 10; j++)
second[j] = first[j];
Data Structures Using C++ 31
Classes and Pointers: Some Peculiarities
class pointerDataClass
{
public:
...
private:
int x;
int lenP;
int *p;
};
pointerDataClass objectOne;
pointerDataClass objectTwo;
Data Structures Using C++ 32
Classes and Pointers: Some Peculiarities
Data Structures Using C++ 33
Destructor
Data Structures Using C++ 34
Destructor
pointerDataClass::~pointerDataClass()
{
delete [ ] p;
}
class pointerDataClass{public: ~pointerDataClass();...private: int x; int lenP; int *p;};
Data Structures Using C++ 35
Assignment Operator
Data Structures Using C++ 36
Assignment Operator
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Assignment Operator
Data Structures Using C++ 38
Overloading the Assignment Operator
Function Prototype (to be included in the definition of the class):const className& operator=(const className&);
Function Definition:const className& className::operator=(const className&
rightObject){ //local declaration, if any if(this != &rightObject) //avoid self-assignment { //algorithm to copy rightObject into this object } //return the object assigned return *this;}
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Overloading the Assignment Operator
• Definition of function operator=:– Only one formal parameter– Formal parameter generally const reference to
particular class– Return type of function is reference to
particular class
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Copy Constructor
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Copy Constructor
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Copy Constructor
Data Structures Using C++ 43
Copy Constructor
• If a class has pointer data members:– During object declaration, the initialization of one
object using the value of another object would lead to a shallow copying of the data if the default memberwise copying of data is allowed
– If, as a parameter, an object is passed by value and the default member-wise copying of data is allowed, it would lead to a shallow copying of the data
Data Structures Using C++ 44
Copy Constructor
• The copy constructor automatically executes in the following situations– When an object is declared and initialized by
using the value of another object– When, as a parameter, an object is passed by
value– When the return value of a function is an object
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Copy Constructor
Data Structures Using C++ 46
Copy Constructor
General syntax to include the copy constructor in the definition of a class:
className(const className& otherObject);
Data Structures Using C++ 47
Classes with Pointer Data Members
• Include destructor in the class
• Overload assignment operator for class
• Include copy constructor
Data Structures Using C++ 48
Overloading Array Index (Subscript) Operator ([ ])
Syntax to declare the operator function operator [ ] as a member of a class for nonconstant arrays:
Type& operator[](int index);
Syntax to declare the operator function operator [ ] as a member of a class for constant arrays:
const Type& operator[](int index) const;
Data Structures Using C++ 49
Chapter Summary
• Pointer data types and variables
• Dynamic variables
• Pointer arithmetic
• Dynamic arrays
• Shallow and deep copying
• Peculiarities of classes with pointer data members