String manipulation in C++ using string library

By Nishtha Grover

In this tutorial, we will see how to perform string manipulation in C++ and learn about various functions of the string library.

A string is a sequence of characters. We use the String library in C++ to create and implement string objects. It has the implementation of a character array.

In C++ we can declare strings in two ways:

1. Create a fixed-size character array.
2. Create a variable size string using the string as the data type.

#include<iostream> 
#include<string>// for string class 
using namespace std; 
int main() 
{ 
    //character array with predefined size = 40
    char char_array[40] = "CodeSpeedy as a character array"; 
  
    // variable sized string
    string str("CodeSpeedy as a string"); 
  
    cout << char_array << endl; 
    cout << str << endl; 
  
    return 0; 
}

String manipulation functions in C++

Some of the commonly used string manipulations functions of the string library in C++

1. length()
   This method finds the length of a given string. It returns an integer value as the length.
2. size()
   This method also finds the length of a given string and returns an integer value.
   
3. concatenation methods
   1. “+” operator:  We can concatenate two strings and assign them to yet another string without affecting the value of the initials strings using this operator.
   2. “+=” operator: We can concatenate two strings and assign them to either of the two strings itself by using this operator.
   3. append(): We can append the values of a string to a given string at the end using this function.
4. clear(): The function of the string library clears all the contents of a given string.
5. empty():  This function checks if the given is empty or not and returns 0 or 1 as output.
6. swap():  This swaps the contents of two strings seamlessly.
7. substr(start_index, no_of_characters*): This returns the substring of a string starting from start index up to the given number of characters. If the optional second argument is not given, it returns a substring up to the end of the string.
8. at(index): This function fetches and returns a character at a given index in the string.
9. replace(start_index, no_of_characters, replace_by): This replaces the given number of characters starting from the start index by the replce_by argument.
10. find (substring): This function returns the index of the first occurrence of the substring and returns -1 if the substring is not found.

The following code illustrates an example of each of the above-discussed functions.

C++ Implementation: Working with string

#include <iostream>
#include <string>

using namespace std;

int main()
{
    string my_string =  "CodeSpeedy";
    
    //find length of the string using length() and size() functions
    int len = my_string.length();
    cout<<len<<endl;
    int size = my_string.size();
    cout<<size<<endl;
    
    
    //concatinating two strings using '+' operator
    string str1 = "Hello";
    string str2 = "world";
    string new_string = str1 + str2;
    cout << new_string << endl;
    
    //concatinating two strings using '+=' operator
    string s1 = "CodeSpeedy";
    string s2 = "tutorials";
    cout<< s1<< endl;
    cout<< s2<< endl;
    s1+=s2;
    cout<< s1<< endl;
    cout<< s2<< endl;
    
    //concatinating two strings using append() function
    string st1 = "CodeSpeedy";
    string st2 = "tutorials";
    cout<< st1<< endl;
    cout<< st2<< endl;
    st1.append(st2);
    cout<< st1<< endl;
    cout<< st2<< endl;
    
    
    //clear a string using Clear() 
    //and check if it is epty using empty() functions
    string str = " Hello World!";
    cout<< str<< endl;
    (str.empty()==1)?cout<<"string empty"
    :cout<<"string not empty"<< endl;
    
    str.clear();
    (str.empty()==1)?cout<<"string empty"
    :cout<<"string not empty"<< endl;
    
    //swapping two strings using swap() function
    string str3 = "Hello";
    string str4 = "world";
    cout<< "str3 = "<<str3<<endl;
    cout<< "str4 = "<< str4<< endl;
    str3.swap(str4);
    cout<< "after swapping :"<< "str3 = "<<str3<<endl;
    cout<< "str4 = "<< str4<< endl;
    
    
    //getting substring from a string using substr().
    cout<<str.substr(2,5)<<endl; // substring from index 2-5
    cout<<str.substr(4)<<endl;//substring starting 
                              //from index 4 to the end of the string
    
    
    //getting a charcter at a particular index using at()
    cout<<str.at(4)<<endl;
    

    //replacing a subtring at a particular index 
    //in a given string with another using replace()
    s = "String manipulation in C++"
    cout<< s << endl;
    s.replace(4,3,"x");
    cout<< s << endl;
    
    //find a given substring in a string using find() function
    t = "thankyou ";
    int index = t.find(th);
    cout<< index << endl;
    
    return 0;
}

Further reading: Find the last index of a character in a string in C++,

Mirror of a string in C++ (Reversal of string) and Removing leading and trailing spaces from a string in C++