[Boost-users] usage of boost::asio::async_write and boost::asio::buffer
Ozgur Ozturk
I am modifying example echo server for my server.
I started to get the attached error, and I suspect I am using buffer incorrectly since error started after a change there.
I just changed a line from
boost::asio::async_write(socket_,
boost::asio::buffer("1^", 3,
boost::bind(&session::handle_write, this,
boost::asio::placeholders::error));
to
boost::asio::async_write(socket_,
boost::asio::buffer(replyString, replyString.size()),
boost::bind(&session::handle_write, this,
boost::asio::placeholders::error));
I generate the replyString to have results from my database query separated with ^ signs (which is used to tokenize the replyString on the client side...)
string replyString="1^";
while(res->next())
{
replyString+=res->getString("nickname")+"^";
}
I checked that replyString.size() is really one more than the final filled position index in replyString.
Any ideas, suggestions?
TIA,
Best regards,
Ozgur (Oscar) Ozturk
www.DrOzturk.com
Phone: +1 (908) DROZGUR
i.e, +1 (908) 376-9487
Igor R
> boost::asio::buffer(replyString, replyString.size()),
> boost::bind(&session::handle_write, this,
> boost::asio::placeholders::error));
>
> I generate the replyString to have results from my database query separated
> with ^ signs (which is used to tokenize the replyString on the client
> side...)
>
> string replyString="1^";
boost::asio::buffer does not copy your local string, so the string
vanishes before the actual async. write takes place.
By the way, if you wish to send the whole string, you don't have to
pass a size: boost::asio::buffer(replyString) - but the string must be
alive until the completion handler is called.
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Ozgur Ozturk
>alive until the completion handler is called.
I tried to use the same string as buffer for both async_read_some and async_write
I guess the string can not be treated as a mutable buffer, so maybe I should keep the original char * buffer for async_read_some and use the string only for outputting with async_write. Is that right?
(or any other recommendation?)
//NOW data_ member variable is string istead of char*
void start()
{
socket_.async_read_some(boost::asio::buffer(data_),
boost::bind(&session::handle_login, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
Error message includes:
c:\program files\boost\boost_1_38\boost\asio\detail\win_iocp_socket_service.hpp(1409) : error C2664: 'boost::asio::mutable_buffer::mutable_buffer(const boost::asio::mutable_buffer &)' : cannot convert parameter 1 from 'const boost::asio::const_buffer' to 'const boost::asio::mutable_buffer &'
Reason: cannot convert from 'const boost::asio::const_buffer' to 'const boost::asio::mutable_buffer'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
You can see the full error messages I get here:
http://pastebin.com/f4ee951e4
TIA
Igor R
Who will allocate the buffer for the read operation? socket's
async_read_some() doesn't know to do this alone.
> I guess the string can not be treated as a mutable buffer, so maybe I should
> keep the original char * buffer for async_read_some and use the string only
> for outputting with async_write. Is that right?
> (or any other recommendation?)
Why wouldn't you use asio::streambuf? You've a set of functions that
async.read/write from/to it, and it grows automatically. You can see
relevant examples in asio docs.