C语言字符串与文件读写函数 fgets(),fputs()......

《C语言入门经典第四版霍顿》 P470

// 从文本文件中读出一个字符串
#include <stdio.h>
#include <stdlib.h> 
// #include <stdbool.h>  // 编译器报错，没有这个文件 据说是bool 类型变量定义的头文件

const int LENGTH = 80;

int main(void)
{
char *proverbs[]=
{
"Many a mickle makes a muckle.\n",
"Too many cooks spoil the broth.\n",
"He who laughs last didn't get the joke in the first place.\n"
};

char more[LENGTH];
FILE *pfile = NULL;
char *filename = "c:\\myfile.txt";

//if(!(pfile = fopen(filename,"w"))) //  因为没有stdbool.h头文件，所以要这句拆开写
    pfile = fopen(filename,"w");
if(pfile==NULL)
{
printf("Error opening %s for writing. Program terminated.",filename);
exit(1);
}

int count = sizeof proverbs/sizeof proverbs[0];  // 难道proverbs每个元素都等长？显然不是，难道他们的分配的空间做了对齐处理了？
for(int i=0;i<count;i++)
fputs(proverbs[i],pfile);   // 从pfile 指向的文件重读取字符串 到 proverbs

 fclose(pfile);

//if(!(pfile = fopen(filename,"a"))) // 以追加的方式打开
pfile = fopen(filename,"a");
if(pfile==NULL)
{
printf("Error opening %s for writing. Program terminated.",filename);
exit(1);
}

printf("Enter proverbs of less than 80 characters or press Enter to end:\n");
while(true)
{
fgets(more,LENGTH,stdin); //读取一条谚语从 键盘 到 more
if(more[0]=='\n')break;  // 如果是空行，则结束读取操作。
fputs(more,pfile); // 输出more 到 pfile
}
fclose(pfile);

//if(!(pfile = fopen(filename,"r"))) // 以只读的方式打开文件
pfile = fopen(filename,"r");
if(pfile==NULL)
{
printf("Error opening %s for reading. Program terminated.",filename);
exit(1);
}
printf("The proverbs in the file are :\n\n");
while(fgets(more,LENGTH,pfile))// 读取一条谚语:从pfile 到 more，(没有遇到EOF ?) 
printf("%s",more);
fclose(pfile);
//remove(filename);

    char readstring[LENGTH];
pfile = fopen(filename,"r");

    fgets(readstring,LENGTH,pfile);// 读取文件的第一行
printf("%s",readstring);

 fgets(readstring,LENGTH,pfile);// 读取文件的第二行
printf("%s",readstring);

 fgets(readstring,LENGTH,pfile);// 读取文件的第三行
printf("%s",readstring);

fgets(readstring,LENGTH,pfile);// 读取文件的第四行，文件只有四行，读完了
printf("%s",readstring);

fgets(readstring,LENGTH,pfile);// 读取文件的第五行，没有第五行了，测试表明还是读取的第四行
printf("%s",readstring);

   fgets(readstring,LENGTH,pfile);// 读取文件的第六行，没有第六行了，测试表明还是读取的第四行
printf("%s",readstring);

fclose(pfile);  // 关闭文件指针
//---
return 0;

}

输出结果：

Enter proverbs of less than 80 characters or press Enter to end:
The proverbs in the file are :

Many a mickle makes a muckle.
Too many cooks spoil the broth.
He who laughs last didn't get the joke in the first place.
test test test
Many a mickle makes a muckle.
Too many cooks spoil the broth.
He who laughs last didn't get the joke in the first place.
test test test
test test test
test test test

1） fgets(readstring,LENGTH,pfile); 每执行一次，刚好读取一行，问题是被读取的文件在被关闭之前，是怎么知道移到下一行的？

难道是文件指针移动了？

2）文件读了4行，已经读完了，再次执行fgets(readstring,LENGTH,pfile);都是输出文件的最后一行，可能文件指针在被关闭前，

指针总之指在每行的开始？

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C语言字符串与文件读写函数 fgets(),fputs()......

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