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). To use stringstream, we need to include sstream header file. The stringstream class is extremely useful in parsing input. 

Basic methods are:

1. clear()- To clear the stream.
2. str()- To get and set string object whose content is present in the stream. 
3. operator <<- Add a string to the stringstream object. 
4. operator >>- Read something from the stringstream object.

Examples:

1. Count the number of words in a string

Examples:

Input: Asipu Pawan Kumar
Output: 3

Input: Geeks For Geeks Ide
Output: 4

Below is the C++ program to implement the above approach-

C++

// C++ program to count words in
// a string using stringstream.
#include <iostream>
#include <sstream>
#include<string>
using namespace std;

int countWords(string str)
{
    // Breaking input into word
    // using string stream

    // Used for breaking words
    stringstream s(str);

    // To store individual words
    string word;

    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

Examples:

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     

Below is the C++ program to implement the above approach-

C++

// C++ program to demonstrate use
// of stringstream to count
// frequencies of words.
#include <bits/stdc++.h>
#include <iostream>
#include <sstream>
#include<string>
using namespace std;

void printFrequency(string st)
{
    // Each word it mapped to
    // it's frequency
    map<string, int>FW;

    // Used for breaking words
    stringstream ss(st);

    // To store individual words
    string Word;

    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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