Copy a streambuf's contents to a string

Question

Apparently boost::asio::async_read doesn\'t like strings, as the only overload of boost::asio::buffer allows me to create const_buffer

Answer 1

Another possibility with boost::asio::streambuf is to use boost::asio::buffer_cast<const char*>() in conjunction with boost::asio::streambuf::data() and boost::asio::streambuf::consume() like this:

const char* header=boost::asio::buffer_cast<const char*>(readbuffer.data());
//Do stuff with header, maybe construct a std::string with std::string(header,header+length)
readbuffer.consume(length);

This won't work with normal streambufs and might be considered dirty, but it seems to be the fastest way of doing it.

Answer 2

It's really buried in the docs...

Given boost::asio::streambuf b, with size_t buf_size ...

boost::asio::streambuf::const_buffers_type bufs = b.data();
std::string str(boost::asio::buffers_begin(bufs),
                boost::asio::buffers_begin(bufs) + buf_size);

Answer 3

A simpler answer would be to convert it in std::string and manipulate it some what like this

 std::string buffer_to_string(const boost::asio::streambuf &buffer)
 {
  using boost::asio::buffers_begin;
  auto bufs = buffer.data();
  std::string result(buffers_begin(bufs), buffers_begin(bufs) + buffer.size());
 return result;
}

Giving a very concise code for the task.

Answer 4

I think it's more like:

streambuf.commit( number_of_bytes_read );

istream istr( &streambuf );
string s;
istr >> s;

I haven't looked into the basic_streambuf code, but I believe that should be just one copy into the string.