Question

I have a wstringstream:

wstringstream sstream;
AlterSstream(sstream);

wstringstream bar_stream;

bar_stream << sstream;
bar_stream << "foo";

MessageBoxW(
  NULL,
  bar_stream.str().c_str(),
  L"subject",
  MB_OK
);

This outputs a long string that looks nothing like what I put in it in AlterSstream():

00000000002CEC58foo

AlterSstream:

void AlterSstream(wstringstream& outStream)
{
    outStream << "odp";
}

Why is this happening? If I print out sstream directly, it works fine, but printing out bar_stream creates the problem. I’m guessing that the << operator doesn’t work the way I think it does between two streams?

UPDATE: Sorry, I had left a bit of code out originally. It is fixed above.

Answer 1

There is no overload to copy from stream to stream.
You need to change the line:

bar_stream << sstream;

to:

bar_stream << sstream.str();