Firstly, I think you need to learn how to use wirshark or tcmpdump to analysis network streams when debugging, that will help you find out the problem and solve it.

As for your program, there are several problems the user207421 has mensioned. I think it's better to use TCP, but if you want to learn UDP by this way, the thing you need is to do a slim reliable UDP by yourself.

For example, you may need the following models

• Build a send buffer and recive buffer, check every time if the buffer is empty, if not, send/receive and process it.

• Add some extra format of information in the head of each datagram, which includes the size of the whole message, the sequence of the datagram, the left size, etc.

• Build a controller, which need to have some function like retransmission, rebuild the message, etc.

Hope that can help you.

Firstly, I think you need to learn how to use wirshark or tcmpdump to analysis network streams when debugging, that will help you find out the problem and solve it.

As for your program, there are several problems the user207421 has mensioned. I think it's better to use TCP, but if you want to learn UDP by this way, the thing you need is to do a slim reliable UDP by yourself.

For example, you may need the following models

• Build a send buffer and recive buffer, check every time if the buffer is empty, if not, send/receive and process it.（Cause UDP has MTU）

• Add some extra format of information in the head of each datagram, which includes the size of the whole message, the sequence of the datagram, the left size, etc.(Cause you need to cut your message into many parts)

• Build a controller, which need to have some function like retransmission, rebuild the message, etc.(Cause UDP is unreliable, you need to check the completeness of all parts)

Hope that can help you.