网络编程学习笔记（一）-----socket

今天开始学习Linux的C++网络编程。

 

以前也用过一点socket，但是没有总结过，今天重新复习，然后总结之。

 

首先介绍一些数据类型：

 

sockaddr_in

sockaddr_un

sockaddr

 

struct sockaddr { __SOCKADDR_COMMON (sa_); /* Common data: address family and length. */ char sa_data[14]; /* Address data. */ };struct sockaddr_un { sa_family_t sun_family; /* AF_UNIX */ char sun_path[UNIX_PATH_MAX]; /* pathname */};/* Structure describing an Internet (IP) socket address. */#define __SOCK_SIZE__ 16 /* sizeof(struct sockaddr) */struct sockaddr_in { sa_family_t sin_family; /* Address family */ __be16 sin_port; /* Port number */ struct in_addr sin_addr; /* Internet address */ /* Pad to size of `struct sockaddr'. */ unsigned char __pad[__SOCK_SIZE__ - sizeof(short int) - sizeof(unsigned short int) - sizeof(struct in_addr)];};

 

这些结构体的定义虽然看起来不同，但是长度是相同的，而且对于处理而言，sockaddr_in显得最为方便，但是为了兼容链接，bind等函数的接口，需要做一个安全的强制类型转换 ：

 

（struct sockaddr*）&some_sockaddr_in_definition

 

剩下一个要点就是理解网络连接的基本过程：

对于服务器端，首先创建socket，然后填写socketaddr_in的内容，这里需要注意的是sin_port的填写需要通过htons()函数对port进行转换。

//htons函数将一个16位数从主机字节顺序转换成网络字节顺序

 

1 bind（）绑定端口

 

2 listen（）

 

3 accept（）等待client的连接

 

4 解析用户的数据

 

5 send()发送给用户数据

 

循环执行3-5

 

代码如下：

#include<sys/types.h>#include<sys/socket.h>#include<stdio.h>#include<sys/un.h>#include<unistd.h>#include<stdlib.h>#include<errno.h>#include<netinet/in.h>#include<sys/wait.h>#include<arpa/inet.h>const int BACKLOG = 10;//接受的没有accept的链接const int PORT = 8611;int main(){int server_sockfd,client_sockfd;struct sockaddr_in sever_addr,client_addr;if( (server_sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){perror("initialize sever socket failed");exit(1);}//set the type of net and the listen portsever_addr.sin_family = AF_INET;sever_addr.sin_port = htons(PORT);sever_addr.sin_addr.s_addr = INADDR_ANY;//set the other bits to zerobzero(&(sever_addr.sin_addr),8);//bindif(bind(server_sockfd,(struct sockaddr*)&sever_addr,sizeof(struct sockaddr_in)) == -1){perror("bind failed");exit(-1);}//listenif(listen(server_sockfd,BACKLOG) == -1){perror("listen failed");exit(-1);}while(1){int sin_size = sizeof(struct sockaddr_in);if((client_sockfd = accept(server_sockfd,(struct sockaddr*)&client_addr,(socklen_t*)&sin_size) )== -1){perror("accept");continue;}printf("server get connect from %s/n",inet_ntoa(client_addr.sin_addr));if(!fork()){if(send(client_sockfd,"Hello world/n",13,0) == -1){perror("send");close(client_sockfd);exit(-1);}close (client_sockfd);}}while( waitpid(-1,NULL,WNOHANG)>0);return 0;}

 

对于客户端来说，情况要更简单一些：

 

1 构造socket，socketaddr_in，这些是和server相同的，不同的是需要构造一个hostent类型的数据

/* Description of data base entry for a single host. */struct hostent{ char *h_name;/* Official name of host. */ char **h_aliases;/* Alias list. */ int h_addrtype;/* Host address type. */ int h_length;/* Length of address. */ char **h_addr_list;/* List of addresses from name server. */#if defined __USE_MISC || defined __USE_GNU# defineh_addrh_addr_list[0] /* Address, for backward compatibility.*/#endif};

 

该实体的构造可以调用函数gethostbyname()（或者为gethostbyaddr()）函数来实现。

 

 

2 connect()

 

3 sent()

 

4 recv()

 

#include<stdio.h>#include<unistd.h>#include<stdlib.h>#include<errno.h>#include<string.h>#include<netdb.h>#include<sys/socket.h>#include<netinet/in.h>#include<sys/types.h>const int PORT = 8611;const int MAX_PACK_LEN = 100;int main(int argc, char **argv){if(argc!=2){printf("Usage : Client hostname/n");exit(-1);}int sockfd,num;char buf[MAX_PACK_LEN];struct hostent *he;struct sockaddr_in client_addr;//get the host informationif( (he =gethostbyname(argv[1]) ) == NULL){herror("gethostbyname");exit(-1);}//creat socketif((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1){perror("Client socket");exit(-1);}//initialize the sockaddr_inclient_addr.sin_family = AF_INET;client_addr.sin_port = htons(PORT);client_addr.sin_addr = *((struct in_addr*)he->h_addr);bzero(&(client_addr.sin_zero),8);//connectif(-1 == connect(sockfd,(struct sockaddr*)&client_addr,sizeof(sockaddr))){perror("client connection");exit(-1);}//receive the dataif( (num = recv(sockfd,buf,MAX_PACK_LEN,0)) == -1){perror("client receive data failed");exit(-1);}//it's the safe method to output the data received!buf[num] = '/0';printf("Received :%s/n",buf);close(sockfd);return 0;}