• C学习笔记-结构体与二进制文件增删改查


    使用结构体整理数据,然后利用二进制存储文件,这样存储的文件类似于数据库,可以实现文件的增删改查

    定义结构体

    struct student
    {
    	unsigned int ID;
    	char name[20];
    };
    

    创建二进制文件

    int main(int argc, char *args[])
    {
    	struct student st[10] = { {1, "a"}, {2, "b"}, {3, "c"}, {4,"d"}, {5, "e"}, {6, "f"}, {7, "g"}, {8, "h"}, {9, "i"}, {10, "j"} };
    
    	FILE *p = fopen("a.dat", "wb");
    	if (p == NULL)
    	{
    		return 0;
    	}
    	fwrite(st, sizeof(struct student), 10, p);//写入10个struct student大小的内容
    	fclose(p);
    	return 0;
    }
    

    读取内容

    int main()
    {
    	FILE *p = fopen("a.dat", "rb");
    	if (p == NULL)
    	{
    		return 0;
    	}
    
    	struct student st;
    	memset(&st, 0, sizeof(st));
    	while (fread(&st, sizeof(st), 1, p))//循环读取文件所有内容
    	{
    		printf("ID = %u, name = %s
    ", st.ID, st.name);
    	}
    	fclose(p);
    	return 0;
    }
    

    替换内容

    int main(int argc, char *args[])//替换第3个元素
    {
    	struct student st = { 3, "zhang" };
    
    	FILE *p = fopen("a.dat", "rb+");
    	if (p == NULL)
    	{
    		return 0;
    	}
    	fseek(p, sizeof(st)* 2, SEEK_SET);//从文件开始位置向后移动两个struct student大小
    	fwrite(&st, sizeof(struct student), 1, p);//将st写入文件
    	fclose(p);
    	return 0;
    }
    

    根据ID查找内容

    int main()//根据用户输入查找指定ID号的同学
    {
    	FILE *p = fopen("a.dat", "rb");
    	if (p == NULL)
    	{
    		return 0;
    	}
    	struct student st;
    	while (1)//循环读取用户键盘输入ID号
    	{
    
    		printf("input ID:");
    		unsigned int ID = 0;
    		scanf("%u", &ID);
    		if (ID == 0)
    			break;
    		clock_t ct = clock();//得到程序当前运行时间,单位毫秒
    		fseek(p, sizeof(st)* (ID - 1), SEEK_SET);//根据用户输入ID好,将位置移动到指定位置
    
    		memset(&st, 0, sizeof(st));
    		fread(&st, sizeof(st), 1, p);//读取指定位置内容
    		ct = clock() - ct;
    		printf("%d
    ", ct);//将代码执行时长打印到屏幕,单位:毫秒
    		printf("ID = %u, name = %s
    ", st.ID, st.name);
    	}
    	fclose(p);
    	return 0;
    }
    

    插入内容

    其主要思想是全部查出,然后添加,再写入

    void insert(struct student array[], int len)
    {
    	for (int i = len - 1; i >= 2; i--)
    	{
    		array[i + 1] = array[i];
    	}
    }
    
    int main()//读取结构体二进制文件所有内容
    {
    	FILE *p = fopen("a.dat", "rb");//只读方式打开二进制文件
    	if (p == NULL)
    	{
    		return 0;
    	}
    	struct student *pst = calloc(100, sizeof(struct student));
    	int index = 0;
    	while (fread(&pst[index++], sizeof(struct student), 1, p) > 0);//循环读取文件所有内容
    	insert(pst, index);
    	pst[2].ID = 100;
    	strcpy(pst[2].name, "zhao");
    	for (int i = 0; i < index + 1; i++)
    	{
    		printf("ID = %u, name = %s
    ", pst[i].ID, pst[i].name);
    	}
    	fclose(p);
    	p = fopen("a.dat", "wb");
    	if (p == NULL)
    	{
    		return 0;
    	}
    	fwrite(pst, sizeof(struct student), 11, p);
    	fclose(p);
    	free(pst);
    	return 
    

    例子

    将txt文本文件转为二进制文件,并随机编号

    #include <stdio.h>
    #include <time.h>
    
    struct student 
    {
    	unsigned int ID;
    	char name[20];
    };
    
    void write_dat()
    {
    	srand((unsigned int)time(NULL));//生成一个随机种子
    	FILE *p1 = fopen("student.txt", "r");//以只读方式打开student.txt文件
    	FILE *p2 = fopen("student.dat", "wb");//以只读方式打开student.txt文件
    	while (!feof(p1))
    	{
    		struct student st = { 0, "" };
    		fgets(st.name, sizeof(st.name), p1);
    		size_t len = strlen(st.name);
    		if (st.name[len - 1] == '
    ')
    		{
    			st.name[len - 1] = 0;
    		}
    		st.ID = rand();
    		fwrite(&st, sizeof(struct student), 1, p2);
    	}
    	fclose(p1);
    	fclose(p2);
    }
    
    
    
    
    int main()
    {
        write_dat();
    	FILE *p = fopen("student.dat", "rb");
    	if (p == NULL)
    	{
    		return 0;
    	}
    	struct student st;
    	while (fread(&st, sizeof(st), 1, p) > 0)
    	{
    		printf("ID = %u, name = %s
    ", st.ID, st.name);
    	}
    	fclose(p);
    	return 0;
    }
    
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  • 原文地址:https://www.cnblogs.com/cj5785/p/10664781.html
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