Linux网络编程

gethostbyname函数的使用例子

下面这个例子使用gethostbuname获得主机相关信息（ip,name等等）#include <stdio.h>#include <unistd.h>#include <sys/types.h>#include <netdb.h>#include <errno.h>#include <netinet/in.h>#include <stdlib.h>int main(int argc,char **argv){ struct hostent *h; if(argc!=2) {fprintf(stderr,"Usage of name!/n");exit(1); } h=gethostbyname(argv[1]); printf("Host name:%s/n",h->h_name); printf("IP Address:%s/n",inet_ntoa(*((struct in_addr *)h->h_addr))); return 0;}

 

具有连接的通信（TCP）

TCP是面向连接的通信，服务端和客户端之间需要建立连接服务端通过监听客户端了解连接情况，保证具有顺序，无差错的通信注意:1.不是客户端一次发送多少数量的数据，服务器端一次就接受多少数据，TCP协议给高层的数据数量，是TCP协议的事情，但是整体来说，保证到服务器端的数据是完整按照顺序到达的2.服务器程序中if((newfd=accept(sockfd,(struct sockaddr *)&their_addr,&sock_len))==-1)fatal("accept");accept函数返回的是一个新的socket描述符以后的通信都是针对这个新的socket描述符操作，而不是以前那个sockfd3.多线程编程中函数pthread_create的第三个参数的原型是void* fun(void *)Server端程序#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <netinet/in.h>#include <sys/types.h>#include <arpa/inet.h>#include <sys/socket.h>#include <pthread.h>#define PORT 5000#define BUFLEN 100int sockfd;int sock_len; int read_num;int newfd;char readbuf[BUFLEN];char writebuf[BUFLEN];void fatal(char *mes){ perror(mes); exit(1);}void* send_message(){ while(1) { gets(writebuf);if(write(newfd,writebuf,BUFLEN)==-1) fatal("write"); }}int main(){ pthread_t pit; struct sockaddr_in my_addr; struct sockaddr_in their_addr; if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)fatal("socket"); my_addr.sin_family=AF_INET; my_addr.sin_port=htons(PORT); my_addr.sin_addr.s_addr=INADDR_ANY; bzero(&(my_addr.sin_zero),0); if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1) fatal("bind"); if(listen(sockfd,5)==-1) fatal("listen"); sock_len=sizeof(struct sockaddr); if((newfd=accept(sockfd,(struct sockaddr *)&their_addr,&sock_len))==-1)fatal("accept"); if(pthread_create(&pit,NULL,send_message,NULL)==-1)fatal("pthread_createa"); while(1) { if((read_num=read(newfd,readbuf,BUFLEN))==-1) fatal("read");readbuf[read_num]='/n';readbuf[read_num+1]='/0'; printf("%s send message:%s/n",inet_ntoa(their_addr.sin_addr),readbuf); } close(sockfd); pthread_join(pit,NULL); exit(0);}Client端程序#include <netinet/in.h>#include <sys/types.h>#include <sys/socket.h>#include <arpa/inet.h>#include <pthread.h>#define PORT 5000#define BUFLEN 100 int sockfd;int read_num;char readbuf[BUFLEN];char writebuf[BUFLEN];void fatal(char *mes){ perror(mes); exit(1);}void* send_message(){ while(1) { gets(writebuf);if(write(sockfd,writebuf,BUFLEN)==-1) fatal("write"); }}int main(){ struct sockaddr_in my_addr; struct sockaddr_in their_addr; pthread_t pit; if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)fatal("socket"); my_addr.sin_family=AF_INET; my_addr.sin_port=htons(PORT); my_addr.sin_addr.s_addr=INADDR_ANY; bzero(&(my_addr.sin_zero),0); their_addr.sin_family=AF_INET; their_addr.sin_port=htons(PORT); their_addr.sin_addr.s_addr=inet_addr("172.18.137.156"); bzero(&(their_addr),0); if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1)fatal("bind"); if(connect(sockfd,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1)fatal("connect"); if(pthread_create(&pit,NULL,send_message,NULL)==-1)fatal("pthrea_create"); while(1) {if((read_num=read(sockfd,readbuf,BUFLEN))==-1) fatal("read");readbuf[read_num]='/n'; readbuf[read_num+1]='/0';printf("server send message:%s/n",readbuf); } pthread_join(pit,NULL); close(sockfd); exit(0);}

 

无连接的通信（UDP）

无连接的通信使用的是运输层的协议：UDP程序采用C／S模型，但Server端并不需要监听Client端的连接请求只需要在默认设置的端口读取数据即可，发送和读取的时报文，既是客户端发送什么数据，服务器端就完整的读取这段数据注意：1。UDP读取数据于TCP的差别2.留意recvfrom函数，其中第六个个参数必须是＆socklen而且事先必须经过socklen=sizeof(struct sockaddr);处理Server程序3.their_addr.sin_addr.s_addr=inet_addr("127.0.0.1");这句必须主义 linux中的sockaddr_in于windows中SOCKADDR_IN的区别4.printf("get packet from %s./n",inet_ntoa(their_addr.sin_addr));#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <sys/wait.h>#define PORT 5000#define MAXBUFLEN 100int main(){ int sockfd; struct sockaddr_in my_addr; struct sockaddr_in their_addr; int addr_len; int numberget; char recvbuf[MAXBUFLEN]; char sendbuf[MAXBUFLEN]; //get a socket desciptor if((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1) {perror("socket");exit(1); } my_addr.sin_family=AF_INET; my_addr.sin_port=htons(PORT); my_addr.sin_addr.s_addr=INADDR_ANY; bzero(&(my_addr.sin_zero),8); their_addr.sin_family=AF_INET; their_addr.sin_port=htons(PORT); their_addr.sin_addr.s_addr=inet_addr("127.0.0.1"); bzero(&(their_addr.sin_zero),8); if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1) {perror("bind");exit(1); } while(1) { scanf("%s",sendbuf); if(sendto(sockfd,sendbuf,100,0,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1){ perror("sendto"); exit(1);}else{ printf("send success!/n");} if((numberget=recvfrom(sockfd,recvbuf,100,0,(struct sockaddr *)&their_addr,&addr_len))==-1){ perror("recvfrom"); exit(1);} printf("get packet from %s/n",inet_ntoa(their_addr.sin_addr.s_addr)); printf("packet is %d datas long./n",numberget); recvbuf[numberget]='/0';printf("buf data is %s/n",recvbuf); } close(sockfd); exit(0);}Client端程序#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <sys/wait.h>#define MYPORT 5000#define MAXBUFLEN 100int main(){ int sockfd; struct sockaddr_in my_addr; struct sockaddr_in their_addr; int addr_len; int numberget; char recvbuf[MAXBUFLEN]; char sendbuf[MAXBUFLEN]; //get a socket descriptor if((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1) { perror("socket");exit(1); } //set host info my_addr.sin_family=AF_INET; my_addr.sin_port=htons(MYPORT); my_addr.sin_addr.s_addr=INADDR_ANY; //set the rest of the struct sockaddr_in zero bzero(&(my_addr.sin_zero),8); //bind if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1) { perror("bind");exit(1); } //take care of this sentence be carefull! addr_len=sizeof(struct sockaddr); while(1) { if((numberget=recvfrom(sockfd,recvbuf,100,0,(struct sockaddr *)&their_addr,&addr_len))==-1) { perror("recvfrom"); exit(1); } //output recv buf and the address of the talker printf("get packet from %s./n",inet_ntoa(their_addr.sin_addr)); printf("packet is %d datas long./n",numberget); recvbuf[numberget]='/0'; printf("buf data is %s/n",recvbuf); // scanf("%s",sendbuf);scanf("%s",sendbuf);if(sendto(sockfd,sendbuf,sizeof(sendbuf),0,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1){ perror("sendto"); exit(1);} } close(sockfd); exit(0);}