Adding To A char array

Hello,

I have a client /server example that I am trying to modify. The client will send a message to the server and then echo it back to the client.

I want to append a string to the message when it gets to the server (just before it goes to the client)

Here is the original source
doc/html/boost_asio/example/cpp03/echo/async_tcp_echo_server.cpp - 1.55.0


Here is my non working attempt but for some reason I just cant get it to work.

Code:

---

        string sToSend(data_);
        sToSend += "<--- this string to append";
        //const char cs = sToSend.c_str();
      socket_.async_read_some(boost::asio::buffer(sToSend.c_str(), max_length),
          boost::bind(&session::handle_read, this,
            boost::asio::placeholders::error,
            boost::asio::placeholders::bytes_transferred));

---

Error:

Code:

---

/usr/include/boost/asio/detail/buffer_sequence_adapter.hpp|212|error: no matching function for call to ‘boost::asio::mutable_buffer::mutable_buffer(const boost::asio::const_buffers_1&)’|

---

Original Code

Code:

---

      tcp::socket socket_;
  enum { max_length = 1024 };
  char data_[max_length];boost::asio::async_write(socket_,          boost::asio::buffer(data_, bytes_transferred),          boost::bind(&session::handle_write, this,            boost::asio::placeholders::error));

---

Code:

---


//
// async_tcp_echo_server.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2013 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#include <cstdlib>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

class session
{
public:
  session(boost::asio::io_service& io_service)
    : socket_(io_service)
  {
  }

  tcp::socket& socket()
  {
    return socket_;
  }

  void start()
  {
    socket_.async_read_some(boost::asio::buffer(data_, max_length),
        boost::bind(&session::handle_read, this,
          boost::asio::placeholders::error,
          boost::asio::placeholders::bytes_transferred));
  }

private:
  void handle_read(const boost::system::error_code& error,
      size_t bytes_transferred)
  {
    if (!error)
    {
      boost::asio::async_write(socket_,
          boost::asio::buffer(data_, bytes_transferred),
          boost::bind(&session::handle_write, this,
            boost::asio::placeholders::error));
    }
    else
    {
      delete this;
    }
  }

  void handle_write(const boost::system::error_code& error)
  {
    if (!error)
    {
      socket_.async_read_some(boost::asio::buffer(data_, max_length),
          boost::bind(&session::handle_read, this,
            boost::asio::placeholders::error,
            boost::asio::placeholders::bytes_transferred));
    }
    else
    {
      delete this;
    }
  }

  tcp::socket socket_;
  enum { max_length = 1024 };
  char data_[max_length];
};

---

Well the error message mentions boost::asio::mutable_buffer::mutable_buffer, which suggests that whatever gets passed in should be susceptible to modification.

A string.c_str() fails to meet this requirement.

You need to allocate a char* block of memory, copy your string to it and then free it when you're done.

Thank you for the reply. I have been trying to get this to work but so far I cannot.


No matter what I do, the same amount of bytes is returned back to the client as was originally read. What am i doing wrong here?

Code:

---

  void handle_read(const boost::system::error_code& error,
      size_t bytes_transferred)
  {

        // data_ here == "thisisatest"
   
    if (!error)
    {
        data_[0] = 'X';                                  // this works
        char * cstr;
        string str (data_);
        str = str + "app";
        cstr = new char [str.size()+1];
        strcpy (cstr, str.c_str());

      // cstr  at this point == "Xhisisatestapp"
        // sizeof(cstr)  == 8  this is not correct


      boost::asio::async_write(socket_,
          boost::asio::buffer(cstr, sizeof(cstr)),          // sizeof(cstr) is not right here  I even try to hardcode this to 12 but it did not work either (only 10 bytes returned to client)
          boost::bind(&session::handle_write, this,
            boost::asio::placeholders::error));

            delete cstr;

// original code
//      boost::asio::async_write(socket_,
//          boost::asio::buffer(data_, bytes_transferred),
//          boost::bind(&session::handle_write, this,
//            boost::asio::placeholders::error));
    }
    else
    {
      delete this;
    }
  }

---

Well it's either str.size() or strlen(cstr)

It's also
delete [] cstr;

Thank you! strlen worked for fixing the size.

I cant thank you enough for your help!

is there a better alternative to getting the char* to a string?

They used this (which is great for writing out to the console but I need it in a string variable)

Code:

---

cout.write(reply, reply_length);

---

// this works (only because the last line with the substr) but seems more like a hack

Code:

---

    #define SSTR( x ) static_cast< std::ostringstream & >(( std::ostringstream() << std::dec << x ) ).str()


    string sReply = SSTR(reply);
    sReply = sReply.substr(0, request_length);

---

This has garbage at the end of it

Code:

---

    stringstream ss;
    string sReply;
    ss << reply;
    ss >> sReply;

---

Use a vector:

std::vector<char> Buf(1024);
// Write to buffer
// Null terminate buffer if boost doesn't
// Now let's add the buffer to the string
MyStr += &Buf[0];

It would be easier if you used boost's streams to do network I/O. I'm sure there must be an example somewhere.