C ++ stringstream

Question

How does stringstream work when you do this:

stringstream ss;
ss << "123" << "abc";

Does it create a throwaway "123abc" string or does it do both operations consecutively to the stringstream?

I would like to replicate that functionality but no overload I do seems to work with two parameters like the above code...

Answer 1

It's the equivalent of doing two seperate function calls of the << operator:

(ss.operator<<("123")).operator<<("abc")

so yes, it does both operations "consecutively".

Answer 2

Actually it is equivalent to this:

std::operator<<(std::operator<<(ss, "123"), "abc");

Note that there is no member function which takes const char* as argument. It is a non-member function, and ss is passed to it as first argument and const char* is passed as second argument. The function returns std::ostream& which then passed to it again. It is more like this:

print( print (ss, "123"), "abc"); //just for clarity

which means there are two function calls. Replace print with std::operator<< . Everything will be clear now.

Hope that helps.

---

The other answer which says this:

(ss.operator<<("123")).operator<<("abc") //copied from other answer (wrong)

is wrong! It is wrong because it assumes that operator<< which takes const char* as argument is a member function which is not true!

Answer 3

std::stringstream::operator<<(const char*) returns a std::stringstream& .

This technique lets you "chain" it.

This is not quite true -- but it is pretty much equivalent to the truth for your purposes.

A slightly more accurate statement is that std::stringstream& operator<<(std::stringstream&, const char*) can be chained.

An even more accurate statement is that ostream& operator<<(ostream&, const char*) exists, and std::stringstream is an ostream , then overload resolution on << calls it.