Stringstream in c++

A stream in c++ is a flow of data into or out to the program. For example, we can say that std::cin is an input stream whose job is to input some data, and std::cout is an output stream whose job is to output or display data. Stringstream in c++ is a class that allows a string object to be treated like a stream. It can be included using #include<sstream> command.

The following diagram shows that stringstream class is derived from iostream class.

Insertion operation

Insertion operation is used to insert value into a stringstream object.

#include<iostream>
#include<sstream>

using namespace std;
int main(){
     stringstream ss;
     ss >> "Hello world!";
return 0;
}

The example shows how string object can inserted in a stringstream variable ss using >> operator. The >> operator return true if succeed, false otherwise.

There are another method to insert value into a stringstream object. Using str method we can take the data string as argument and assigned the data string to the stringstream variable.

#include<iostream>
#include<sstream>

using namespace std;
int main(){
     stringstream ss;
     ss.str("Hello world!");
return 0;
}

This program does the same job as the above program.

Extraction operation

Extraction operation is used to get data from a stringstream object.

#include<iostream>
#include<sstream>

using namespace std;
int main(){
     stringstream ss.str("Hello world!");
     string str;
     ss >> str;   // str variable get the value of ss
     cout << str;     // this line output 'Hello world!'
return 0;
}

Here in this example, extraction operator >> is use to extract the data from a stringstream object. We use a string obj str to store the value.

#include<iostream>
#include<sstream>

using namespace std;
int main(){
     stringstream ss.str("Hello world!");
     cout << ss.str();    // this line output 'Hello world!'
return 0;
}

Here in this example, str() function is used to get the value stored in stringstream.

Practical use

Using stringstream is useful to get integer type data from a given string. Suppose, we have a string my_string which contains "10,20,30" string. So, how can we extract the integers from the given string. Impossible right?
stringstream can be useful solve this type of problems.

#include<iostream>
#include<sstream>

using namespace std;
int main(){
     string my_string = "10,20,30";     // given string
     stringstream ss.str(my_string);     // passing the my_string object to the str method
     int a,b,c;
     char ch;
     ss >> a >> ch >> b >> ch >> c ;     // now the value of a = 10, b = 20, c = 30, and ch = ','
     // ch variable is used for get the inner commas
     cout "a:"<< a << ", b:" << b << ", c:" << c << endl;
     return 0;
}

The above code out put the following result-

     a:10, b:20, c:30

What next?

Hope you understand the basic concept of using stringstream.
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