about string streams?

[Dy7SLyTq]

ive googled them, but i cant find a good explanation of them. what do they do that class istream doesnt?

[cire]

If you've googled them, pretty much any link you click with example code will show them doing something that can't be done with an istream or ostream.

[MiiNiPaa]

//Third party library header
class Money
{
    private:
        int cents;
    public:
        Money(int _cents) : cents(_cents) {};
    friend std::ostream & operator<< (std::ostream & , Money);
};

//Third party precompiled library 
std::ostream & operator<< (std::ostream & left, Money right)
{
    left << (right.cents/100) << '.' << (right.cents % 100);
    return left;
}

//Our 10 years old library
void legacy_function(char*);

//We need to make them to go along:
int main()
{
    Money pay(654);
    stringstream x;
    x << pay;
    legacy_function( x.str().c_str() );
}

[JLBorges]

> what do they do that class istream doesnt?

Nothing, except for a class-specific constructor and the member function str().

The heavy lifting is done by std::stringbuf.
std::istringstream is just ultra-thin facade over a std::istream that is composed with a std::stringbuf.

#include <iostream>
#include <sstream>

int main()
{
    std::stringbuf buf( "0 1 2 3 4 5 how now brown cow.", std::ios::in ) ;
    auto stdinbuf = std::cin.rdbuf( &buf ) ;

    int i ; while( std::cin >> i ) std::cout << i << ' ' ; // 0 1 2 3 4 5
    std::cout << '\n' ;

    std::cin.clear() ;
    std::string s ; std::getline( std::cin, s ) ;
    std::cout << s << '\n' ; // how now brown cow.

    std::cin.rdbuf(stdinbuf) ;
}

http://liveworkspace.org/code/2haWvs$0