I am writing a small Java server, and a matching client in C++, which implement a simple IM service over the STOMP protocol.

The protocol specifies that every frame (message that passes between server and client, if you will) must end with a null character, which in code I refer to as '\0', both in Java and in C++.

However, when I transmit a frame over TCP via sockets, the null character simply does not show up, on either side. I am working with UTF-8 encoding, and tried switching to ASCII, didn't help.

What am I doing wrong?

Wether you are encoding text in ASCII or UTF-8, you convert your "letters" to a stream of bytes (byte encodings). You need to add a ZERO byte to the end of the message strings.

[Guessing] You may be using a high-level library with a method like "WriteLine(String line)" to send the data over the network. The documentation for that method with describe what bytes are actually sent, which typically includes the message text encoding in the current encoding (ASCII, UTF-8, etc) followed by a line termination sequence, which is typically either the byte 13, 10m or a combination of them ('\n', '\r\n').

Use the low-level Write() method or WriteBytes() method (depending on your libraries). Convert the text to ASCII or UTF-8, add the zero byte to the end, and send exactly what you want to send.