文件编程（二）

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标准I/O库

C标准库提供了操作文件的标准I/O函数库，与系统调用相比，主要差别是实现了一个跨平台的用户态缓冲的解决方案。

一个I/O缓冲的例子如下：

1、fopen():

#include <stdio.h>int main(){FILE *fp = fopen("test3","ab+");if(fp == NULL){perror("fopen");return -1;}printf("打开文件成功\n");    return 0;}

2、fread():

#include <stdio.h>#define SIZE 1024int main(){FILE *fp = fopen("BTree.c", "ab+");if(fp == NULL){perror("fopen");return -1;}char buf[SIZE] = {0};int ret = 0;while(ret = fread(buf, sizeof(char), SIZE - 1, fp)){buf[ret*sizeof(char)] = '\0';printf ("%s\n", buf);}if(ret == 0 && !feof(fp)){perror("fread");return -1;}printf("文件读取结束\n");fclose(fp);    return 0;}

3、fwrite():

#include <stdio.h>#define SIZE 1024int main(){FILE *fp1 = fopen("1.ppt", "ab+");if (fp1 == NULL){perror ("fopen1");return -1;}FILE *fp2 = fopen("2.ppt", "ab+");if (fp2 == NULL){perror ("fopen2");return -1;}char buf[SIZE] = {0};int ret = 0;while(ret = fread(buf,sizeof(char),SIZE,fp1)){fwrite(buf,sizeof(char),ret,fp2);}if(ret == 0 && !feof(fp1)){perror("fread");return -1;}printf("文件复制成功\n");fclose(fp1);fclose(fp2);    return 0;}

4、在文件中存取结构体数据

#include <stdio.h>#define SIZE 1024typedef struct student{int  id;char name[20];}STU;void write_data(STU *a,int len){FILE *fp = fopen("student", "ab+");if (fp == NULL){perror ("fopen");return;}// 要写入个数printf("len = %d\n",len);fwrite(&len, sizeof(int), 1, fp);int i;for (i = 0; i < len; i++){// 写入数据长度int count = sizeof(a[i]);fwrite(&count, sizeof(int), 1, fp);// 写入数据fwrite(&a[i], sizeof(STU), 1, fp);}fclose(fp);}void read_data(){FILE *fp = fopen("student", "ab+");if (fp == NULL){perror ("fopen");return;}// 读记录的个数int count;fread (&count, sizeof(int), 1, fp);printf ("记录个数是：%d\n", count);int i;STU tmp;for (i = 0; i < count; i++){int len;fread (&len, sizeof(int), 1, fp);// 读取数据fread (&tmp, len, 1, fp);printf ("id = %d, name = %s\n", tmp.id, tmp.name);}fclose(fp);}int main(){int i;STU a[20];int len = sizeof(a) / sizeof(a[0]);for (i = 0; i < 20; i++){a[i].id = i;sprintf (a[i].name, "zhang%d", i);}// 写入数据write_data(a,len);// 读数据//read_data();    return 0;}

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