为什么我不能使用 fseek() 访问 EOF？

Question

#include <stdio.h>

int main()
{
    FILE * fp = fopen("Introduce.txt","rt");

    fseek(fp,0,SEEK_END);
    int i = feof(fp);
    printf("%d",i);

    fseek(fp,1,SEEK_END);
    i = feof(fp);
    printf("%d",i);

    fseek(fp,-1,SEEK_END);
    i = feof(fp);
    printf("%d",i);

    return 0;
}

我试图在文件末尾访问 EOF 定位 'file position indicator'。
但是这段代码的结果是“000”。为什么会这样？

Answer 1

feof() 函数不会报告它处于 EOF，直到您尝试读取一些数据并且没有数据可读取。

您可以在打开以写入（或打开以读取和写入）的文件的当前 EOF 之外进行搜索。

请参阅 while (!feof(file)) is always wrong 以了解有关您很少需要使用 feof() 的原因的更多信息。在某些方面，feof() 是一个你应该忘记的函数——如果你假设它不存在，你的大多数程序都会改进。

Answer 2

This documentation on feof很清楚（强调我的）：

This function only reports the stream state as reported by the most recent I/O operation, it does not examine the associated data source. For example, if the most recent I/O was a fgetc, which returned the last byte of a file, feof returns zero. The next fgetc fails and changes the stream state to end-of-file. Only then feof returns non-zero.

In typical usage, input stream processing stops on any error; feof and ferror are then used to distinguish between different error conditions.

为什么我不能使用 fseek() 访问 EOF？

Why can't I access EOF using fseek()?

c

file

eof