Today’s Class

• Class string– The basics– Assignment– Concatenation– Compare & swap– Find– Conversion to C-style char * strings– Iterators

Reminders

• Final Exam– Thursday, December 19th, 12:00 – 2:00 pm– Covers last 1/3 of class

• Course grade– Will be posted Friday morning– Exams = 300 points– Assignment = 250 points– Total = 550 points

Class String

• Template class basic_string– String manipulation operations such as copying,

searching, etc.– Template definition in namespace std

• typedef basic_string< char > string;

• Need the following in a file– #include <string>– using std::string;– string str;

Constructors

• Have several different ways of initializing a string (see constructors.txt)string s1("cat");

string s2 = "dog";

string s3(5, 'z'); (string "zzzzz")

string s4; //default constructor

string s5 = s1; //copy constructor

string s6(s2); //copy constructor

Possible Errors

• No conversion from int or char– These will create a compiler error

• string error1 = 'c';• string error2( 'u' );• string error3 = 22;• string error4( 8 );

– Can only assign a character in this manner• s1 = 'X'; • s2.at(0) = 'X'; • s3[1] = 'X';

Properties• Different than C-style strings

– The terminating NULL (‘\0’, or 0) character not necessary

– Is not a pointer

• Has numerous member functions– Most member functions take a starting

subscript location & number of characters• If number of characters is too large, max chosen• Will not give STATUS_ACCESS_VIOLATION

or “bus error” as in C

Basic Functions

• Number of characters– str.length() returns the length of a string– A string starts a subscript 0 and ends at

subscript str.length() – 1– Can also use str.size()

• Access individual characters– str[5] or str.at(5)

• at( ) provides range checking (but [ ] does not)

• at( ) will throw an out_of_range exception

I/O

• Stream extraction• cin >> str;

– Delimited by whitespace characters

• getline( cin, str);– Delimited by newline

• Stream insertion• cout << str;

Assignment

• Have several different ways– (See assignment.txt)string str1("string"), str2, str3,

str4, str5;

str2 = str1;

str3.assign(str1);

Assignment• Can assign character-by-character

– But don’t forget to resize it, as a default string has 0 length

str4.resize(str1.length());for(i=0;i<str1.length();i++)

str4[i]=str1[i];

str5.resize(str1.size());for(i=0;i<str1.size();i++)

str5.at(i)=str1[i];

Concatenation

• Also many ways to do thisstr3 += str1 + "SSSSS";

//str3 = stringSSSSS

str4.append(str1 + "SSSSS");

//str4 = stringSSSSS

str5.append(str1, 1, 4);

//str5 = stringtrin

//(str1’s 1st to 4th elements)

string str6(str1 + " and " + str2);

//str6 = string and string

Comparing

• Can use the overloaded operators• >, <, >=, <=, ==, !=

– Return bool values (true = 1, false = 0)

– Have to keep in mind the ASCII values for characters

– For example, all capital letters have a lower value than lowercase letters

– So: 'A' < 'Z' < 'a' < 'z'

Comparing & Swapping

• Or use compare() function - A.compare(B)– If A equals B, returns 0– If A is greater than B, returns positive number– If A is less than B, returns negative number

• Use function swap() to swap two strings– A.swap(B);

• See compare.txt for some examples

Class Exercise 1

• What’s the output of this program?– See exercise1.txt

Characteristics (char.txt)• Member functions: size(), length()

– Number of characters currently stored in the string

• Member function: capacity()– Number of characters that can be stored

without increasing the memory capacity of the string

• Member function: max_size()– Largest possible string that can be stored

• Member function: empty()– Whether the string is empty or not

Find Functions (find.txt)

• A.find(“string”)– Attempts to find the substring in A– If found, returns the starting location of the

first matching substring– If not, returns string::pos (a constant defined

in class string)

• A.rfind(“string”)– Same, but starts on the right and searches to

the left

Convert to C-style Strings

• Have to take several steps (convert.txt)string str1("This is a string.");

int len = str1.length();

char *str2 = new char[ len + 1 ];

//save space for null

str1.copy( str2, len, 0 );

// copy characters out of string into allocated memory

str2[ len ] = 0;

//add null terminator

Convert to C++-style Strings

• At least three ways– Use a constructor

string str3(str2);

– Use a for loop string str4;

str4.resize(len);

for(int i=0;i<len;i++) str4[i]=str2[i];

– Use an iterator

Iterators• Using an iterator to traverse a string

string str5; str5.resize(len); string::iterator i = str5.begin(); k = 0; while(i != str5.end()){

*i = str2[k]; i++; k++;

} cout << "str5 = "<<str5<<endl;

Iterators• Iterators have many features in common

with pointers– Used to point to the elements in a container

• Container = generic (template) data structures

– The dereferencing operator (*) dereferences an iterator, so you can use the element to which it points

– Increment (++) and decrement (--) operators are used to move to the next element of the container

Iterators

• Container functions used with iterators– begin()

• Returns an iterator pointing to the first element of the container

– end()• Returns an iterator pointing to the first element

past the end of the container

Iterators

• Have two types of iterators– An object of type iterator

• Refers to a container object that can be modified

– An object of type const_iterator• Refers to a container object that cannot be

modified

Class Exercise 2

• What’s the output of this program?– See exercise2.txt