Manipulating Strings in C++

Introduction

A string is a sequence of character.
We have used null terminated <char> arrays (C-strings or C-style strings) to store and manipulate strings.
ANSI C++ provides a class called string.

Commonly Used String Constructors

String();   
// For creating an empty string.
String(const char *str);   
// For creating a string object from a null-terminated string.
String(const string &str);   
// For creating a string object from other string object


Creating String Objects

string s1, s3;    // Using constructor with no arguments.
string s2(“xyz”);    // Using one-argument constructor.
s1 = s2;        // Assigning string objects
s3 = “abc” + s2;    // Concatenating strings

cin >> s1;        // Reading from keyboard (one word)
cout << s2;        // Display the content of s2
getline(cin, s1)    // Reading from keyboard a line of text

s3 += s1;        // s3 = s3 + s1;
s3 += “abc”;        // s3 = s3 + “abc”;

Manipulating String Objects

string s1(“12345”);
string s2(“abcde”);

s1.insert(4, s2);        // s1 = 1234abcde5

s1.erase(4, 5);        // s1 = 12345

s2.replace(1, 3, s1);    // s2 = a12345e




Relational Operations

Operator        Meaning

==               Equality
!=                 Inequality
<                  Less than
<=               Less than or equal
>                  Greater than
>=               Greater than or equal

string s1(“ABC”); string s2(“XYZ”);
int x = s1.compare(s2);
x == 0 if s1 == s2
x > 0 if s1 > s2
x < 0 if s1 < s2


String Characteristics

void display(string &str)
{
    cout << “Size = ” << str.size() << endl;
    cout << “Length = ” << str.length() << endl;
    cout << “Capacity = ” << str.capacity() << endl;
    cout << “Max Size = ” << str.max_size() << endl;
    cout << “Empty: ” << (str.empty() ? “yes” : “no”) << endl;
    cout << endl << endl;
}


Accessing Characters in Strings
Function            Task

size()                      Number of elements currently stored
length()                 Number of elements currently stored
capacity()              Total elements that can be stored
max_size()             Maximum size of a string object that a  system  can support
emply()                  Return true or 1 if the string is empty otherwise returns false or 0
resize()                   Used to resize a string object (effects only size and length)