linux系统和网络(四):网络

????????本文主要探讨linux网络相关知识,详细介绍看本博客其他博文。

网络基础(参考本博客其他文章：基础网络知识，socket网络编程，基于socket的聊天室和简易ftp)
????????路由器是局域网和外部网络通信出入口
????????DNS实现域名和IP地址之间转换
????????NAT是局域网主机发送数据包给外网将主机内网IP转换为外网IP
????????网段 = IP地址 & 子网掩码

demo:

? ? ? ? 编写client和server,server用于存储个人信息，client下发个人信息增删改查等信息到server,server执行并反馈结果

server

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>          
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>

#define SERPORT         8001
#define SERADDR         "192.168.200.181"
#define BACKLOG         100

#define CMD_REGISTER            1
#define CMD_CHECK               2
#define CMD_GETINFO             3
#define CMD_DELETE              4

typedef struct people_info
{
        char name[20];
        int age;
        int cmd;
        char result[20];
} info;

typedef struct mark_flag
{
        int flg;
        int zero;
} mark;

char name[3][10] = {0};
int age[3] = {0};
int cli_fd;
info st;
mark flag;

void have_connect()
{
        struct sockaddr_in ser_addr = {0};
        struct sockaddr_in cli_addr = {0};
        socklen_t len = sizeof(cli_addr);

        int sockfd = socket(AF_INET,SOCK_STREAM,0);
        if(sockfd == -1)
        {
                perror("socket");
                exit(-1);
        }

        ser_addr.sin_family = AF_INET;
        ser_addr.sin_port = htons(SERPORT);
        ser_addr.sin_addr.s_addr = inet_addr(SERADDR);
        bind(sockfd, (const struct sockaddr *)&ser_addr, sizeof(ser_addr));

        listen(sockfd, BACKLOG);

        cli_fd = accept(sockfd, (struct sockaddr *)&cli_addr,&len);
        send(cli_fd,"connect sucess",strlen("connect sucess"),0);
        printf("%s connect ...\n",inet_ntoa(cli_addr.sin_addr));

}


void find_info()
{
        int i;
        for(i = 0;i < (sizeof(age)/sizeof(age[0]));i++)
        {
                if(!strncmp(name[i],st.name,strlen(st.name)))
                        flag.flg = i;
                if(age[i] == 0)
                        flag.zero = i;
        }
}

void register_info()
{
        find_info();
        if(flag.flg != -1)
        {
                strcpy(st.result,"user existed");
        }

        if(flag.zero == -1 &&  flag.flg == -1)
        {
                strcpy(st.result,"user full");
        }

        if(flag.zero != -1 && flag.flg == -1)
        {
                strcpy(name[flag.zero],st.name);
                age[flag.zero]  = st.age;
                strcpy(st.result,"register ok");
        }

}

void get_info()
{
                        find_info();
                        if(flag.flg == -1)
                        {
                                strcpy(st.result,"have no user");
                        }
                        else
                        {
                                st.age = age[flag.flg];
                                strcpy(st.name,name[flag.flg]);
                        }
}

void check_info()
{
                        find_info();
                        if(flag.flg == -1)
                        {
                                strcpy(st.result,"have no user");
                        }
                        else
                        {
                                strcpy(st.result,"user existed");
                        }
}

void delete_info()
{
                        find_info();
                        if(flag.flg == -1)
                        {
                                strcpy(st.result,"have no user");
                        }
                        else
                        {
                                age[flag.flg] = 0;
                                memset(name[flag.flg],0,sizeof(name[flag.flg]));
                                strcpy(st.result,"user deleted");
                        }
}

int main()
{
        have_connect();

        while(1)
        {
                memset(&st,0,sizeof(st));
                recv(cli_fd, &st, sizeof(info), 0);
                memset(st.result,0,sizeof(st.result));
                flag.flg = -1;
                flag.zero = -1;
                if(st.cmd == CMD_REGISTER)
                {
                        register_info();
                }

                if(st.cmd == CMD_GETINFO)
                {
                        get_info();
                }

                if(st.cmd == CMD_CHECK)
                {
                        check_info();
                }
                if(st.cmd == CMD_DELETE)
                {
                        delete_info();
                }
                send(cli_fd,&st,sizeof(st),0);
        }

        return 0;
}

client?

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>          
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>

#define SERPORT         8001
#define SERADDR         "192.168.200.181"

#define CMD_REGISTER            1
#define CMD_CHECK               2
#define CMD_GETINFO             3
#define CMD_DELETE              4

typedef struct people_info
{
        char name[20];
        int age;
        int cmd;
        char result[20];
} info;

int sockfd;
info st;

void have_connect()
{
        struct sockaddr_in ser_addr = {0};
        char buf[20] = {0};

        sockfd = socket(AF_INET,SOCK_STREAM,0);
        if(sockfd == -1)
        {
                perror("socket");
                exit(-1);
        }

        ser_addr.sin_family = AF_INET;
        ser_addr.sin_port = htons(SERPORT);
        ser_addr.sin_addr.s_addr = inet_addr(SERADDR);
        bind(sockfd, (const struct sockaddr *)&ser_addr, sizeof(ser_addr));

        connect(sockfd, (const struct sockaddr *)&ser_addr, sizeof(ser_addr));
        recv(sockfd,buf, sizeof(buf), 0);
        printf("%s\n",buf);
}

int main()
{
        int flag;
        have_connect();
        while(1)
        {
                memset(&st,0,sizeof(st));
                printf("ex:1 : register 2 : check 3 : get 4 : delete,please input:");
                scanf("%d",&flag);
                if(flag ==1)
                {
                        printf("name:");
                        scanf("%s",st.name);
                        printf("age:");
                        scanf("%d",&st.age);
                        st.cmd = CMD_REGISTER;
                }
                else
                {
                        printf("name:");
                        scanf("%s",st.name);
                        if(flag ==2)
                                st.cmd = CMD_CHECK;
                        if(flag ==3)
                                st.cmd = CMD_GETINFO;
                        if(flag ==4)
                                st.cmd = CMD_DELETE;
                        if(flag == 0 || flag > 4)
                                printf("input error\n");
                }
                send(sockfd,&st,sizeof(st),0);
                recv(sockfd,&st, sizeof(st), 0);
                if(strlen(st.result))
                {
                        printf("%s\n",st.result);
                }
                else
                {
                        printf("name : %s, age : %d\n",st.name,st.age);
                }
        }
}

结果显示：