stringstream in C++ and its applications

A stringstream associates a string object with a stream allowing you to read from the string as if it were a stream (like cin).

Basic methods are –

clear() — to clear the stream
str() — to get and set string object whose content is present in stream.
operator << — add a string to the stringstream object.
operator >> — read something from the stringstream object,

stringstream class is extremely useful in parsing input.

Applications :

1. Count number of words in a string

   Examples:
   Input : Asipu Pawan Kumar
   Output : 3
   
   Input : Geeks For Geeks Ide
   Output : 4

   // CPP program to count words in a string
   // using stringstream.
   #include <bits/stdc++.h>
   using namespace std;
   
   int countWords(string str)
   {
       // breaking input into word using string stream
       stringstream s(str); // Used for breaking words
       string word; // to store individual words
   
       int count = 0;
       while (s >> word)
           count++;
       return count;
   }
   
   // Driver code
   int main()
   {
       string s = "geeks for geeks geeks "
                  "contribution placements";
       cout << " Number of words are: " << countWords(s);
       return 0;
   }
   

   Output:

     Number of words are: 6

2. Print frequencies of individual words in a string

   Input : Geeks For Geeks Quiz Geeks Quiz Practice Practice
   Output : For -> 1
            Geeks -> 3
            Practice -> 2
            Quiz -> 2
   
   Input : Word String Frequency String
   Output : Frequency -> 1
            String -> 2
            Word -> 1 
   

   // CPP program to demonstrate use of stringstream
   // to count frequencies of words.
   #include <bits/stdc++.h>
   using namespace std;
   
   void printFrequency(string st)
   {
       // each word it mapped to it's frequency
       map<string, int> FW;
       stringstream ss(st); // Used for breaking words
       string Word; // To store individual words
   
       while (ss >> Word)
           FW[Word]++;
   
       map<string, int>::iterator m;
       for (m = FW.begin(); m != FW.end(); m++)
           cout << m->first << " -> "
                << m->second << "\n";
   }
   
   // Driver code
   int main()
   {
       string s = "Geeks For Geeks Ide";
       printFrequency(s);
       return 0;
   }
   

   Output:

   For -> 1
   Geeks -> 2
   Ide -> 1
   

3. Removing spaces from a string using Stringstream
4. Converting Strings to Numbers in C/C++

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