222 lines
4.5 KiB
Markdown
222 lines
4.5 KiB
Markdown
---
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title: C语言-5
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date: 2022-12-20 20:02
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tags: [C语言, 笔记]
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categories: 笔记
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thumbnail: "https://t.alcy.cc/fj"
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---
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## 打开与关闭文件
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### 1、用fopen打开文件
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- fopen(文件名，使用文件方式)
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```c
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fopen("D:\\date\\Mystudio\\demo.txt","r+");
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fopen("D:/date/Mystudio/demo.txt","r+"); //绝对路径
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```
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- fopen函数的返回值是只要操作文件(demo.txt)的指针，若出错，将返回一个空指针(NULL)。
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- 因此，一般是将fopen函数返回值赋给一个指向文件的指针变量。
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```c
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FILE *fp; //定义一个文件指针
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//打开一个文件，"r+"表示可读可写的模式打开
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fp = fopen("D\\date\\Mystudio\\demo.txt","r+");
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if(fp==NULL)
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printf("文件demo打开失败");
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else
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printf("文件demo打开成功");
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fclose(fp); //关闭文件
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```
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### 2、用fclose关闭文件
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- fclose(文件指针);
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```c
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fclose(fp);
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```
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- 如不关闭文件就结束程序可能会丢失数据。
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- fclose函数也会返回一个值，当成功执行了关闭为文件操做，返回值为0，否则返回EOF(-1);
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## 顺序读写数据文件
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### 向文件读写字符
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#### 1、fgetc(fp) 从fp指向的文件读入一个字符
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- 读成功则返回所读的字符，失败则返回u文件结束标志EOF(-1);
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```c
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char c=fgetc(fc);
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```
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#### 2、fputc(ch.fp); 把字符ch写道文件指针变量fp所指向的文件中
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- 输出成功，则返回值就是输出的字符，失败就会返回EOF(-1);
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#### 3、feof(fp)函数用来判断文件是否结束
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- 如果遇到文件结束，函数feo(fp)的值为非零值，否则为0
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```c
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char c;
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c = fuputc(ch.fp)
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while(!feof(fp))
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{
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printf("%c",c);
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c = fputc(ch,fp);
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}
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//输出文件中的所有字符
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```
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### 向文件读写字符串
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#### 1、fgets(str,n,fp)从fp指向的文件读如一个长度为(n-1)的字符串
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- 读成功则返回地址str，否则返回NULL;
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```c
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FILE *fp;
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char c[15];
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fp = fopen("D:/date/Mystudio/demo.txt","r+");
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fgets(c,15,fp);
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print("%s",c);
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```
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#### 2、fputs(str,fp)把str指向的字符串写道文件指针变量fp所指向的文件中
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- 输出成功则返回 0 ，否则返回非0值
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```c
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FILE *fp;
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char c[15]={"Hello Linux."};
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fp = fopen("d/date/Mystdio/demo.txt","r+");
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fputs(c,fp);
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```
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### 用格式化方式读写文本
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#### fprint(文件指针，格式字符串，输出列表)格式化输出字符
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```c
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FILE *fp;
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fp = fopen("D;/date/Mystudio/demo.txt","r+");
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int i =5;
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float f = 6.5;
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fprint(fp,"i = %d,f = %6.2f",i,f);
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```
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#### 2、fcanf(文件指针，格式字符串，输出列表)格式化读入字符
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```c
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FILE *fp;
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fp - fopen("D:/dete/Mystudio/demo.txt","r+");
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int i;
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float f;
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fscanf(fp,"%d%f",&i,&f);
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printf("%6.2f",i+f);
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```
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### 用二进制方式向文件读写一组数据
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#### 1、fwrite(butter,size,count,fp);向文件写数据块
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| 名字 | 解释 |
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| ------ | -------------- |
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| butter | 地址 |
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| size | 字节数 |
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| count | 要写多少数据块 |
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| fp | FILE类型指针 |
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```c
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#include <stdio.h>
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#include <stdio.h>
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struct Student
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{
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char name[20];
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char addr[20];
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}s1[3]={
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{"lingren","Daoqi120"},
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{"zhongli","liyue100"},
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{"baerzebu","Daoqi100"},
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};
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int main()
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{
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FILE *fp;
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fp = fopen("E:/USERS/桌面文件/test.txt","r+");
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int i;
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for(i=0;i<3;i++)
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fwrite(&s1[i],sizeof(struct Student),1,fp);
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fclose(fp);
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wreturn 0;
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}
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```
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#### 2、fread(buffer,size,count,fp); 从文件中读数据块
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### 五、随机读写数据文件
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#### 1、rewind函数 使文件位置标记指向文件开头
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#### 2、fseek(文件类型指针，位移量，起始点) 改变文件位置标记
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```c
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fseek(fp,0,SEEK_SET); //光标移动到文件开头后往后偏移0个字节的位置
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#include <stdio.h>
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#include <stdlib.h>
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struct Student
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{
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char name[10];
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char addr[10];
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}s1[4]={
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{"lingren","Daoqi120"},
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{"zhongli","liyue100"},
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{"baerzebu","Daoqi100"},
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};
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int main()
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{
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FILE *fp;
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fp = fopen("E:/USERS/桌面文件/test.txt","r+");
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int i;
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for(i=0;i<3;i++)
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fwrite(&s1[i],sizeof(struct Student),1,fp);
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fseek(fp,sizeof(struct Student),SEEK_SET);
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fread(&s1[3],sizeof(struct Student),1,fp);
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printf("%s,%s",s1[3].name,s1[3].addr);
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fclose(fp);
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return 0;
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}
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```
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### 六、文件读写出错检测
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#### 1、ferror(fp) 检测是否出错
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```c
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#include<stdio.h>
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int main(void)
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{
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FILE* fp;
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fp = fopen("demo.txt","w");
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fgetc(fp);
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if (ferror(fp))
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{
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printf("读取出错\n");
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printf("%d\n",ferror(fp));
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clearerr(fp);
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printf("%d\n",ferror(fp));
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}
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fclose(fp);
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return 0;
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}
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``` |