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;
}