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C++ istream::operator>>() function

The C++ std::istream::operator>>() function is an extraction operator used to read the formatted data from a stringstream object into variables. It works similar to the >> operator with std::cin, but instead, it extracts data from a string buffer.

This function has 3 polymorphic variants: with using the arithmetic type or stream buffers or manipulators (you can find the syntaxes of all the variants below).

Following is the syntax for std::istream::operator>>() function.

istream& operator>> (bool& val);
istream& operator>> (short& val);
istream& operator>> (unsigned short& val);
istream& operator>> (int& val);
istream& operator>> (unsigned int& val);
istream& operator>> (long& val);
istream& operator>> (unsigned long& val);
istream& operator>> (long long& val);
istream& operator>> (unsigned long long& val);
istream& operator>> (float& val);
istream& operator>> (double& val);
istream& operator>> (long double& val);
istream& operator>> (void*& val);
or
istream& operator>> (streambuf* sb );
or
istream& operator>> (istream& (*pf)(istream&));
istream& operator>> (ios& (*pf)(ios&));
istream& operator>> (ios_base& (*pf)(ios_base&));

• val − It indicates the object where the value that the extracted characters represent is stored.
• sb − It indicates the pointer to a basic_streambuf object on whose controlled output sequence the characters are copied.
• pf − It indicates a function that takes and returns a stream object.

This function returns the basic_istream object (*this).

If an exception is thrown, the object is in a valid state.

Modifies val or the object pointed by sb.

Let's look at the following example, where we are going to read the single integer.

#include <iostream>
#include <sstream>
#include <string>
int main()
{
    std::string a = "11";
    std::stringstream b(a);
    int x;
    b >> x;
    std::cout << "Result : " << x << std::endl;
    return 0;
}

Output of the above code is as follows −

Result : 11

Consider the following example, where we are going to read multiple data types.

#include <iostream>
#include <sstream>
#include <string>
int main()
{
    std::string a = "11 2.3 TutorialsPoint";
    std::stringstream b(a);
    int x;
    float y;
    std::string z;
    b >> x >> y >> z;
    std::cout << "x : " << x << ", y : " << y << ", z : " << z << std::endl;
    return 0;
}

Following is the output of the above code −

x : 11, y : 2.3, z : TutorialsPoint

In the following example, we are going to read the list if integers.

#include <iostream>
#include <sstream>
#include <string>
#include <vector>
int main()
{
    std::string x = "1 2 3 4 5";
    std::stringstream y(x);
    std::vector<int> a;
    int b;
    while (y >> b) {
        a.push_back(b);
    }
    std::cout << "Result :";
    for (int n : a) {
        std::cout << " " << n;
    }
    std::cout << std::endl;
    return 0;
}

If we run the above code it will generate the following output −

Result : 1 2 3 4 5

istream.htm

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