Chapter 13 – C++ String Class

String objects

Do not need to specify size of string object– C++ keeps track of size of text– C++ expands memory region to store text as

needed Can use operators to perform some string

manipulations

Lesson 13.1

Declaring string Objects

Use the class name string and list object names

Example: string s1, s2, s3;– s1, s2, s3 would be string objects

String header needed to declare string objects

Do NOT specify size (Note: no brackets)

Initializing string Objects

Can initialize with the =– C++ automatically reserves sufficient memory

Can also place in ( ) but still need " " Null character not required for string text Data member of string class stores size of

text

Lesson 13.1

s1 = "This is an example.";

Operators + string Objects

Lesson 13.1

Type Operator ActionAssignment = Stores string

+= Concatenates and storesComparison == True if strings identical

!= True if strings not identical > True if first string greater than second < True if first string is less than second>= True if first string greater or equal than second<= True if first string less or equal than second

Input/Output >> For input and string objects<< For output and string objects

Character [ ] To access individual characters accessConcatenation + Connects two strings

C Strings vs. string Objects

Older code uses C strings C strings more basic – faster execution String class improves ability to manipulate

text safely– Sized automatically– No null necessary– Easier modification in program

Lesson 13.1

Some Member Functions

More actions needed than operators can provide

Calling member function involves using object name with dot operator and function name– Invoking object

One that is modified

Lesson 13.2

find Function Searches for a string within a string Basic form of call to find

ob1.find (ob2);– finds first occurrence of string ob2 within ob1

Returns position

Lesson 13.2

s1 = "This is an example.";s2 = "exam";n = s1.find (s2);

0 1 2 3 4 5 6 7 8 9 0 1

The return value is 11

Overloaded find Function

Another version has two arguments Basic form: ob1.find (ob2, index);

– index represents integer value for beginning of search

C++ performs automatic type conversion from C strings to string objects when C strings are in string function call

String not found returns -1

Lesson 13.2

replace Function

Replaces characters within a string object with another string

Returns reference to invoking object Basic form: ob1.replace (index, num, ob2);

– index represents position to begin– num is the number of characters to replace– ob2 what is to be used to replace (can be C string)

Overloaded: ob1.replace (index1, num1, ob2, index2, num2);

Lesson 13.2

portion of ob2 to use

erase Function

Eliminates characters within string object Basic form: ob1.erase (index, num);

– num represents number of characters to erase– index is the beginning position

Returns reference to the invoking object

Lesson 13.2

s1 = "This is an example.";s1.erase (8,3);

example.";

insert Function

Adds characters to a string object Basic form: ob1.insert (index, ob2);

– index is beginning position– ob2 represents what is to be inserted

Can be a C string

Returns reference to the invoking function

Lesson 13.2

s1 = "This is an example.";s1.insert (8,"just ");

just an example.";

Other string Functions

Many other functions available– Examples: compare, append, resize, etc.

Described in text, table 13.2– List of functions– Sample syntax– What they return– Description of purpose

Lesson 13.2

Reading a Single Word

From keyboard using cin cin >> s1;– Reads characters until whitespace typed – Whitespace includes space and "Enter" key

Amount of memory for s1 automatically made sufficient

Lesson 13.3

Reading Multiple Lines Use function getline

– Contained in <string> General form: getline (cin, ob1, 'terminator');

– Ob1 is name of string object– Terminator is terminating character

Read but not included in ob1 object Default value is '\n'

Read single line of input: getline (cin, ob1);

Lesson 13.3

Reading an Input File

Use getline for complete file– Read each line into 1-D array of string objects

Use for loop General form:

for ( int j = 0; j < num_lines; j++) { getline (infile, array_element); }

Lesson 13.3

Strings and Functions

Return type for function is string object string objects passed like other objects

– Copy is passed when type string is argument Keyword const prevents array elements

from being modified & indicates a reference

Lesson 13.4

string function1 (string, const string[ ], string&, string [ ]);

Class Definition: Example

Lesson 13.5

class Class1 { private: char aa [20]; string s1; public: char* get_aa( ); string get_s1 ( ); void read_data ( ); };

Both C strings and string objects can be members

of a class

"get" functions returnprivate data memberFunction reads both

data members

Member Functions

Lesson 13.5

class Class1 { private: char aa [20]; string s1; public: char* get_aa( ); string get_s1 ( ); void read_data ( ); };

void Class1 :: read_data ( ) { cout << "Enter your name." << endl; getline (cin ,s1); cout<< "Enter phone number." <<endl; cin.getline (aa) }

char* Class1 :: get_aa ( ) { return aa; }

string Class1 :: get_s1 ( ) { return s1; }

Working With a Class

Object of class declared – allows member functions to be called

Example:

Class1 ob1;ob1.read_data ( );cout <<ob1.get_s1<<endl<<ob1.get_aa ( ) <<endl;

Lesson 13.5

Summary

Create strings with the C++ string class Manipulate strings with string functions Read a word, or multiple lines from

keyboard Use the string class in programs

Learned how to: