下面是UDP的服务器的代码：
/* server.c */#include#include #include #include #include #include "wrap.h"#define MAXLINE 80#define SERV_PORT 8000int main(void){ struct sockaddr_in servaddr, cliaddr; socklen_t cliaddr_len; int sockfd; char buf[MAXLINE]; char str[INET_ADDRSTRLEN]; int i, n; sockfd = wrap_socket(AF_INET, SOCK_DGRAM, 0); bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = htonl(INADDR_ANY); servaddr.sin_port = htons(SERV_PORT); wrap_bind(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr)); printf("Accepting connections ...\n"); while(1) { cliaddr_len = sizeof(cliaddr); n = recvfrom(sockfd, buf, MAXLINE, 0, (struct sockaddr *)&cliaddr, &cliaddr_len); if(n == -1) { perr_exit("recvfrom error"); } printf("received from %s at port %d\n", inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)), ntohs(cliaddr.sin_port)); for(i = 0; i < n; ++i) { buf[i] = toupper(buf[i]); } n = sendto(sockfd, buf, n, 0, (struct sockaddr *)&cliaddr, sizeof(cliaddr)); if(n == -1) perr_exit("sendto error!"); }}
客户端代码：
/* client.c */#include#include #include #include #include #include "wrap.h"#define MAXLINE 80#define SERV_PORT 8000int main(int argc, char *argv[]){ struct sockaddr_in servaddr; int sockfd, n; char buf[MAXLINE]; char str[INET_ADDRSTRLEN]; socklen_t servaddr_len; sockfd = wrap_socket(AF_INET, SOCK_DGRAM, 0); bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr); servaddr.sin_port = htons(SERV_PORT); while(fgets(buf, MAXLINE, stdin) != NULL) { n = sendto(sockfd, buf, strlen(buf), 0, (struct sockaddr *)&servaddr, sizeof(servaddr)); if(n == -1) perr_exit("sendto error"); n = recvfrom(sockfd, buf, MAXLINE, 0, NULL, 0); if(n == -1) perr_exit("recvfrom error"); wrap_write(STDOUT_FILENO, buf, n); } wrap_close(sockfd); return 0;}
由于server和client没有先建立连接然后通信的条件，所以server可以有并发能力。
用Ctrl+C关闭server，然后再运行server，client还能和server联系上。