UDP客户端不从C中的服务器接收任何内容

So I am trying to make a basic server and client using UDP and C,in Linux. The server must receive from the client two char arrays(buffer and aux), and the client must receive from the server an int array which will contain the positions where the character given in aux is in the buffer array (for example, if we have aaabaa, and a in aux, the client must print 01245). The problem is that the client always print 00000 etc, depending on the length of the frecv array.So I am trying to make a basic server and clien