How to get characters out of stringstream without copy?

What is the proper c++11 way to extract a set of characters out of a stringstream without using boost?

I want to do it without copying, if possible, because where this is used is in a critical data loop. It seems, though, std::string does not allow direct access to the data.

For example, the code below performs a substring copy out of a stringstream:

inline std::string left(std::stringstream ss, uint32_t count) {
    char* buffer = new char[count];
    ss.get(buffer, count);
    std::string str(buffer);  // Second copy performed here
    delete buffer;
    return str;
}

1. Should I even be using char *buffer according to c++11?


2. How do I get around making a second copy?

My understanding is that vectors initialize every character, so I want to avoid that.

Also, this needs to be passed into a function which accepts const char *, so now after this runs I am forced to do a .c_str(). Does this also make a copy?

It would be nice to be able to pass back a const char *, but that seems to go against the "proper" c++11 style.

To understand what I am trying to do, here is "effectively" what I want to use it for:

fprintf( stderr, "Data: [%s]...", left(ststream, 255) );

But the c++11 forces:

fprintf( stderr, "Data: [%s]...", left(str_data, 255).c_str() );

How many copies of that string am I making here?

How can I reduce it to only a single copy out of the stringstream?