How to get length of std::stringstream without copying

Question

How can I get the length in bytes of a stringstream.

stringstream.str().length();

would copy the contents into std::string. I don't want to make a copy.

Or if anyone can suggest another iostream that works in memory, can be passed off for writing to another ostream, and can get the size of it easily I'll use that.

Answer 1

Assuming you're talking about an ostringstream it looks like tellp might do what you want.

Answer 2

A solution that provides the length of the stringstream including any initial string provided in the constructor:

#include <sstream>
using namespace std;

#ifndef STRINGBUFFER_H_
#define STRINGBUFFER_H_

class StringBuffer: public stringstream
{
public:
    /**
     * Create an empty stringstream
     */
    StringBuffer() : stringstream() {}

    /**
     * Create a string stream with initial contents, underlying
     * stringstream is set to append mode
     *
     * @param initial contents
     */
    StringBuffer(const char* initial)
        : stringstream(initial, ios_base::ate | ios_base::in | ios_base::out)
    {
        // Using GCC the ios_base::ate flag does not seem to have the desired effect
        // As a backup seek the output pointer to the end of buffer
        seekp(0, ios::end);
    }

    /**
     * @return the length of a str held in the underlying stringstream
     */
    long length()
    {
        /*
         * if stream is empty, tellp returns eof(-1)
         *
         * tellp can be used to obtain the number of characters inserted
         * into the stream
         */
        long length = tellp();

        if(length < 0)
            length = 0;

        return length;

    }
};