warning: pointer targets in passing argument 3 of ‘accept’ differ in signedness

The first warning tells you you have the wrong type for parameter 3 of accept. It wants a 'socklen_t *', but you are giving it an 'int *'. Declare client_length to be the right type.

     socklen_t  len=sizeof(struct sockaddr);
 改为：
     int  len=sizeof(struct sockaddr);