How to efficiently copy istringstream?

Or ostringstream?

istringstream a("asd");
istringstream b = a; // This does not work.

I guess memcpy won't work either.

From stackoverflow

• You can't just copy streams, you have to copy their buffers using iterators. For example:

  #include <sstream>
  #include <algorithm>
  ......
  std::stringstream first, second;
  .....
  std::istreambuf_iterator<char> begf(first), endf;
  std::ostreambuf_iterator<char> begs(second);
  std::copy(begf, endf, begs);
  

  Łukasz Lew : Isn't copying one character at a time slow?

  AraK : Have you measured it?

  Łukasz Lew : I measured it when input was a file ifstringstream. The difference was tremendous.

  AraK : There is nothing called ifstringstream in C++. Could you post the code you wrote?

  AraK : Why would you copy the contents of fstream into stringstream?

• istringstream a("asd");
  istringstream b(a.str());
  

  Edit: Based on your comment to the other reply, it sounds like you may also want to copy the entire contents of an fstream into a strinstream. You don't want/have to do that one character at a time either (and you're right -- that usually is pretty slow).

  // create fstream to read from
  std::ifstream input("whatever");
  
  // create stringstream to read the data into
  std::istringstream buffer;
  
  // read the whole fstream into the stringstream:
  buffer << input.rdbuf();
  

  AraK : +1 I didn't know there is an overloading for buffers!

  Jerry Coffin : Yeah, it's one of those cute little tricks that almost nobody knows about. Not useful all that often, but when you want what it does, it makes things quite a bit simpler.

  Allen George : Shouldn't that be `ostringstream` instead of `istringstream`?