【问题描述】

以树形结构实现域名的搜索，即输入某站点的域名，在域名系统的树形结构中进行搜索，直至域名全部全部匹配成功或者匹配失败，若成功则给出该节点的IP地址，否则给出找不到该节点信息。

【基本要求】

首先实现一个反映域名结构的树，如清华大学站点为www.tsinghua.edu，在该树从根到叶子的各层节点就应该是root、cn、edu、tsinghua、www。叶子结点www另有一个数据域，存放清华大学站点的IP地址166.111.9.2

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct app {
	char a[20];
	struct app *left;
	struct app *right;
	char b[20];
} app;
int cout = 0;
/*建树时用到的数据：com baidu www 220.181.27.5 # # google www 66.249.89.104 # #
 microsoft www 207.46.20.60 # # # gov whitehouse www 64.215.166.127 # #
 nasa www 210.254.57.56 # # # cn com lenovo www 219.239.195.11 # #
 sina www 218.30.13.51 # # # edu ustc www 202.38.64.2 # bbs 202.38.64.3 # #
 pku www 162.105.129.12 # bbs 162.105.204.150 # # tsinghua www 166.111.4.100 #
 ftp 166.111.8.229 # # # gov beijing www 210.73.64.10 # #
 shanghai www 61.129.65.58 # # # # #
*/

//数据保存在相同目录下的text.txt文件下;
app *jianshu(app *bt, FILE *fp) {
	char a[20];
	if (fscanf(fp, "%s ", &a) != EOF) {
		if (a[0] == '#')
			bt = NULL;
		else {
			bt = (app *)malloc(sizeof(app));
			strcpy(bt->a, a);
			if (strcmp(a, "www") == 0 || strcmp(a, "bbs") == 0 || strcmp(a, "ftp") == 0 ) {
				fscanf(fp, "%s ", &a);
				strcpy(bt->b, a);
			}
			bt->left = jianshu(bt->left, fp);
			bt->right = jianshu(bt->right, fp);
		}
	}
	return bt;
}

app *tianjia(app *bt, char fenge[4][20], int i, char ip[20]) {
	/*puts(fenge[i]);
	puts(bt->a);
	printf("%d", i);*/
	if (bt != NULL && strcmp(bt->a, fenge[i]) == 0) {
		if (i == 0) {
			puts(bt->b);
			return bt;
		}
		bt->left = tianjia(bt->left, fenge, --i, ip);
	} else {
		if (bt == NULL) {
			if (i == -1) {
				return bt;
			}
			bt = (app *)malloc(sizeof(app));
			bt->right = NULL;
			bt->left = NULL;
			strcpy(bt->a, fenge[i]);
			if (strcmp(fenge[i], "www") == 0 || strcmp(fenge[i], "bbs") == 0 || strcmp(fenge[i], "ftp") == 0 ) {
				strcpy(bt->b, ip);
			}
			bt->left = tianjia(bt->left, fenge, --i, ip);
		} else
			bt->right = tianjia(bt->right, fenge, i, ip);
	}
	return bt;
}

void qianxu(app *bt, FILE *fp) {
	if (bt == NULL) {
		fprintf(fp, "# ");
	} else {
		fprintf(fp, "%s ", bt->a);
		if (strcmp(bt->a, "www") == 0 || strcmp(bt->a, "bbs") == 0 || strcmp(bt->a, "ftp") == 0 ) {
			fprintf(fp, "%s ", bt->b);
		}
		qianxu(bt->left, fp);
		qianxu(bt->right, fp);
	}
}

void jiediangeshu(app *bt, char fenge[4][20], int i) {
	/*for (i; i >= 0; i--) {
		puts(fenge[i]);
	}*/
	//puts(bt->a);
	//puts(fenge[i]);
	if (bt != NULL && strcmp(bt->a, fenge[i]) == 0) {
		if (i == 0) {
			puts(bt->b);
			return;
		}
		jiediangeshu(bt->left, fenge, --i);

	} else {
		if (bt == NULL) {
			printf("找不到服务器或发生 DNS 错误");
			return;
		}
		jiediangeshu(bt->right, fenge, i);
	}
}

int main() {
	printf("欢迎使用IP查询!\n");
	char str[80];
	char ip[20];
	char *token;
	char ju = 'y';
	int xuan;
	char fenge[4][20];
	int flag = 0;
	app *bt;
	FILE *fp1 = NULL;
	FILE *fp2 = NULL;
	fp1 = fopen("text.txt", "r");
	bt = jianshu(bt, fp1);
	fp2 = fopen("text.txt", "w");
	//qianxu(bt);
	while (ju != 'n') {
		printf("请选择功能：1，增加网址；2，查询网址;3,退出系统\n");
		scanf("%d", &xuan);
		getchar();
		if (xuan == 3) {
			qianxu(bt, fp2);
			exit(0);
		}
		printf("请输入地址：");
		scanf("%s", &str);
		getchar();
		int i = 0;
		token = strtok(str, ".");
		while (token != NULL) {
			strcpy(fenge[i], token);
			i++;
			token = strtok(NULL, ".");
		}
		switch (xuan) {
			case 1:
				printf("请输入ip：");
				scanf("%s", &ip);
				getchar();
				bt = tianjia(bt, fenge, --i, ip);
				break;
			case 2:
				jiediangeshu(bt, fenge, --i);
				break;
		}
		printf("是否继续？y/n\n");
		scanf("%c", &ju);
		//qianxu(bt, fp2);
		getchar();
	}
	qianxu(bt, fp2);
	fclose(fp2);
	fclose(fp1);
	printf("谢谢使用");
}
/*
测试数据
www.baidu 220.181.27.5
www.google 66.249.89.104
www.microsoft 207.46.20.60
www.whitehouse.gov 64.215.166.127
www.nasa.gov 210.254.57.56
www.lenovo 219.239.195.11
www.sina 218.30.13.51
www.ustc.edu 202.38.64.2
bbs.ustc.edu 202.38.64.3
www.pku.edu 162.105.129.12
bbs.pku.edu 162.105.204.150
www.tsinghua.edu 166.111.4.100
ftp.tsinghua.edu 166.111.8.229
www.beijing.gov 210.73.64.10
www.shanghai.gov 61.129.65.58
*/

二叉树结构如图