Strings in C

1
Strings in C

• Chapter 4
• p 125 - 131

2
The string Class

• The C Standard Library includes a string class.
• include ltstringgt

3
C Strings

• C strings are objects.
• NOT arrays
• Assignment works
• str1 str2
• Concatenation
• str3 str1 str2
• str1 str2

4
Class string

• Class methods handle memory allocation for the
  string.
• Memory allocation is automatically increased as
  needed.
• No problems with array bounds overrun.

5
String Methods

• Methods and operators of class string replace C
  String Library functions.
• Example
• str1.size() returns length of str1
• The C comparison operators are defined for
  class string. You can write
• if (str1 lt str2)
• if (str1 str2)
• etc.

6
String Operators

• The C comparison operators are defined for
  class string. You can write
• if (str1 lt str2)
• if (str1 str2)
• etc.
• The operator is defined as concatenation.
• You can write
• str3 str1 str2
• str1 str2

7
Using C Style Strings in C

• String literals are C style strings
• Array of char
• But we can use them with C strings.
• C operators are overloaded to take C styles
  strings as operands.
• Instantiation
• string str1 "abcdef"
• Assignment
• str1 "abcdef"
• Concatenation
• str2 str1 "ghijkl"
• str1 "ghijkl"

8
String I/O

• cin and cout work for strings.
• cout ltlt str1 ltlt endl
• cin gtgt str2 Reads one word
• getline(cin, str3) Reads entire line

9
Example

• Create a new empty C console application
  project.
• string_demo
• Add main.cpp
• We will look at several examples

10
Word at a Time Input

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main()
• string str1
• while (true)
• cout ltlt "Enter a string "
• cin gtgt str1
• cout ltlt "You entered " ltlt str1
• cout ltlt endl

11
Word at a Time Input
12
Line at a Time Input

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main()
• string str1
• while (true)
• cout ltlt "Enter a string "
• getline(cin,str1)
• cout ltlt "You entered " ltlt str1
• cout ltlt endl

13
Line at a Time Input
14
Comparison

• int main()
• string str1
• string str2
• while (true)
• cout ltlt "Enter a string "
• getline(cin,str1)
• cout ltlt "You entered " ltlt str1
• cout ltlt endl
• cout ltlt "Enter another string "
• getline(cin, str2)
• if (str1 lt str2)
• cout ltlt """" str1 """ is less
  than "
• """" str2 """" ltlt endl

15
Using the Less Than Operator
16
Using the string Class

• Let's revise class Circle to use a string for the
  name member.
• Download most recent project
• http//www.cse.usf.edu/turnerr/Object_Oriented_De
  sign/Downloads/2011_02_02_Operator_Overloading/
• File Circle_Sort2.zip
• Copy Circle.h and Circle.cpp into project
  directory.
• Add to project.

17
Circle.h

• ifndef CIRCLE_H
• define CIRCLE_H
• include ltiostreamgt
• using namespace std
• class Circle
• public
• static const int Max_Name 20
• private
• char nameMax_Name1
• double radius
• public
• Circle(const char Name, double Radius)
• Circle()
• double Radius() const return radius

18
Circle.cpp

• define _CRT_SECURE_NO_WARNINGS
• include ltstring.hgt
• include ltiostreamgt
• include "Circle.h"
• using namespace std
• CircleCircle(const char Name, double Radius)
• strncpy(name, Name, Max_Name)
• nameMax_Name 0 // Be sure there is a
  null terminator
• radius Radius

19
Circle.cpp

• double CircleArea() const
• return 3.141592 radius radius
• void CircleDisplay() const
• cout ltlt name ltlt " is a Circle of radius "
• ltlt radius ltlt stdendl
• ...
• ostream operatorltlt(ostream os, const Circle c)
• os ltlt c.Name() ltlt " Radius " ltlt c.Radius()
• return os

20
Circles_Test.cpp

• define _CRT_SECURE_NO_WARNINGS
• include ltiostreamgt
• include ltstringgt
• include "Circle.h"
• using namespace std
• Circle Create_Circle()
• char nameCircleMax_Name1
• double radius
• cout ltlt "Name? "
• cin gtgt name
• cout ltlt "Radius? "
• cin gtgt radius
• return new Circle(name, radius)

21
Circles_Test.cpp

• int main(void)
• Circle c1 Create_Circle()
• cout ltlt "Area of circle " ltlt c1-gtName()
• ltlt " is " ltlt c1-gtArea() ltlt endl
• cin.get() // Keep the window open.
• cin.get()
• return 0
• Build and run.

22
Program Running
23
Using String Class

• Now let's modify class Circle to use a C String
  for name.

24
Changes to Circle.h

• pragma once
• include ltstringgt
• using namespace std
• class Circle
• //public
• // static const int Max_Name 10
• private
• string name
• double radius
• public
• // Constructor
• Circle(const string Name, double Radius)
• // Return the area of this circle.
• double Area()

25
New Constructor

• define _CRT_SECURE_NO_WARNINGS
• include ltstring.hgt
• include ltiostreamgt
• include "Circle.h"
• using namespace std
• CircleCircle(const string Name, double Radius)
• name Name
• radius Radius

26
New Create_Circle Function

• define _CRT_SECURE_NO_WARNINGS
• include ltiostreamgt
• include "Circle.h"
• using namespace std
• Circle Create_Circle()
• string name
• double radius
• cout ltlt "Name? "
• cin gtgt name
• cout ltlt "Radius? "
• cin gtgt radius
• return new Circle(name, radius)

This still works!
27
Main is Unchanged
28
Summary

• The string class in C permits us to treat
  strings as objects rather than as arrays.
• MAJOR improvement over C style strings.
• End of Presentation