IO复用高级应用：同时处理TCP和UDP服务
一个socket只能与一个socket地址绑定即一个socket只能监听一个端口，服务器如果要同时监听多个端口就必须创建多个socket，若在同一个端口监听多个服务也要创建多个socket绑定到这个端口上。现在服务器监听一个端口上的TCP和UDP请求，并将发送来的数据回射到客户端。
服务端程序：
#include<sys/socket.h>#include<netinet/in.h>#include<arpa/inet.h>#include<assert.h>#include<stdio.h>#include<unistd.h>#include<string.h>#include<stdlib.h>#include<iostream>#define BUF_SIZE 1024using namespace std;int main(int argc,char* argv[]){ if(argc<=2){ cout<<"argc<=2"<<endl; return 1; } const char* ip=argv[1]; int port=atoi(argv[2]); struct sockaddr_in server_address; bzero(&server_address,sizeof(server_address)); server_address.sin_family=AF_INET; inet_pton(AF_INET,ip,&server_address.sin_addr); server_address.sin_port=htons(port); int sockfd=socket(PF_INET,SOCK_STREAM,0); int sockudp=socket(PF_INET,SOCK_DGRAM,0); assert(sockfd>=0); if(connect(sockfd,(struct sockaddr*)&server_address,sizeof(server_address))<0){//TCP数据发送与接收 cout<<"connect error"<<endl; return 1; } else{ const char* tcp="this is TCP data\n"; send(sockfd,tcp,strlen(tcp),0); char buf[BUF_SIZE]; int ret=recv(sockfd,buf,BUF_SIZE-1,0); if(ret<0){ cout<<"recv tcp error"<<endl; } else{ buf[ret+1]='\0'; cout<<ret<<" "<<buf<<endl; } } if(connect(sockudp,(struct sockaddr*)&server_address,sizeof(server_address))<0){//UDP数据发送与接收 cout<<"connect error"<<endl; return 1; } else{ const char* udp="this is UDP data\n"; send(sockudp,udp,strlen(udp),0); char buf[BUF_SIZE]; int ret=recv(sockudp,buf,BUF_SIZE-1,0); if(ret<0){ cout<<"recv udp error"<<endl; } else{ buf[ret+1]='\0'; cout<<ret<<" "<<buf<<endl; } } close(sockfd); return 0;}