Visual Studio (C++)：如何使用 TCP 套接字发送多个值？

Question

it's probably a pretty basic question, but I couldn't really find something online so I hope you can help me out here::)

I'm currently working with C++ in Visual Studio and I'm trying to send different variables via TCP Connection at the same time. But I'm not quite sure, what the best way to do it would lookn' like.

I was thinking about sending a long string at once with all variables and between every variable there could be a symbol which shows the end of the variable, just like:

123.45@16.45@33@true@.....

but the programm has to run as fast as possible. A algorithm which sorts every income variables doesn't sound pretty efficient, does it?

The second thought was to create a socket for every variable I got, with a different Port. But I'm not quite sure if that isn't a dirty programming behavior.

So what do you think? Any ideas/experiences?

Thanks in Advance!

Answer 1

Before answering this question, we need to be aligned with some concepts.

TCP is a stream protocol. It's like you're accessing a regular file, but socket API encapsulates many complex tasks from users. When you do a write on a socket, you always append to this socket's TCP stream. So accessing the same socket from two different threads will not give you what you want, instead two different atomic data segments added to TCP stack (you have just made 2 append operation to the stream).

"sending at the same time" may have 2 different meanings:

i) sending the variables at the same TCP session.

In this case, TCP session is no different than writing to a binary file. This is rather a serialization problem than a network protocol problem in that case. You have many options:

a) convert everything to the string representation and send this buffer (fairly slow and inefficient). This is the simplest method. You also need some additional protocol to handle written data as you mentioned (adding @ in between). JSON or XML are good examples of that.

b) if you know the exact order to write and read (encode/decode) just write ints, char arrays, shorts, longs as binary (hey float and double serialization may not be that straightforward). Decoder will read binary data in the exact same order. Remember to convert network byte-order if you pick this solution.

ii) sending the variables simultaneously

If you really want to send many variables at the same time (i mean almost simultaneously), then you'd better to have many threads and many sockets at that case. Maybe you are reading integer sensor data from one sensor which creates thousands of integer in a second, and double values from another sensor. The meaning of simultaneously here is that you do not have to wait for reading the whole bunch of integers to read doubles or vice versa. This also saves encoding/decoding time.