C语言用fgetc()读文件错误

Question

C语言使用fgetc读取文件出错。

#include<stdio.h>
#include<string.h>
#include<conio.h>

int main() {
    FILE *fp;
    unsigned char ch;
    int num[8]; 
    int count = 0;
    
    fp = fopen("2.txt","r");
    while( (ch = fgetc(fp)) != 255){
        for(int i=0;i<8;i++){
            num[i] = ch>>(7-i)&1;
            printf("%d",num[i]);
        }
        
        printf(" ");
        if (++count == 8) {
            printf("\n");
            count = 0;
        }
        getch();
    }
    fclose(fp);
}

读取的文件在这里：www.ewinds.pw/2.txt

很奇怪，用自己写的程序读取文件，结果是这样的：

用ultreaEdit读取出来结果如下：

想要知道为什么读取到第二十一个字节，一直往后，全部变成了1111 1111.
求大家指点，不甚感激

Answer 1

fp = fopen("2.txt","rb");

---

#include <stdio.h>
#include <string.h>
#include <conio.h>
#include <stdlib.h>

int main(void)
{
    FILE* fp = fopen("2.txt", "rb");
    if(!fp) {
        printf("File opening failed\n");
        return EXIT_FAILURE;
    }

    int count = 0;
    int c; // note: int, not char, required to handle EOF
    while ((c = fgetc(fp)) != EOF) { // standard C I/O file reading loop
        for(int i=0;i<8;i++){
            printf("%d", c>>(7-i)&1);
        }
        printf(" ");
        if (!(++count%8)) {
            printf("\n");
        }
        //getch();
    }

    if (ferror(fp))
        printf("\nI/O error when reading\n");
    else if (feof(fp))
        printf("\nEnd of file reached successfully\n");

    fclose(fp);
    getch();
    return 0;
}

结果

00000000 00000000 00000000 00000000 00100001 11100100 11000110 11111010
00000000 00000000 00000000 00000000 00101101 10111001 00000100 00101010
00000000 00000000 00000000 00000000 00011010 00001011 11011010 11001110
00000000 00000000 00000000 00000000 00101011 11000101 01011111 00101101
00000000 00000000 00000000 00000000 00000011 00101011 11101001 11101001
00000000 00000000 00000000 00000000 00110000 01010101 10011111 11111111
00000000 00000000 00000000 00000000 00001001 00011000 11000011 00100110
00000000 00000000 00000000 00000000 00001111 00001110 00010100 11011010
00000000 00000000 00000000 00000000 00100000 00001101 11100111 10101011
00000000 00000000 00000000 00000000 00101011 11000101 01011111 00101101
00000000 00000000 00000000 00000000 00100100 10100111 00101111 01100111
00000000 00000000 00000000 00000000 00000101 01100100 01011001 01111000
00000000 00000000 00000000 00000000 00011001 11100101 10100010 10001101
00000000 00000000 00000000 00000000 00011110 00010001 10101001 01010000
00000000 00000000 00000000 00000000 00000011 00101011 11101001 11101001
00000000 00000000 00000000 00000000 00010101 11100000 01100000 10100111
00000000 00000000 00000000 00000000 00001000 11001111 11000001 10000010
00000000 00000000 00000000 00000000 00100000 00101110 11001100 00101011
00000000 00000000 00000000 00000000 00110110 01001010 00110001 10000111
00000000 00000000 00000000 00000000 00000011 00101011 11101001 11101001
00000000 00000000 00000000 00000000 00110000 01010101 10011111 11111111
00000000 00000000 00000000 00000000 00001001 00011000 11000011 00100110
00000000 00000000 00000000 00000000 00001111 00001110 00010100 11011010
00000000 00000000 00000000 00000000 00101001 10100011 10010000 11111011
00000000 00000000 00000000 00000000 00011110 01100001 00101000 01000000
00000000 00000000 00000000 00000000 00001100 11101000 11111001 00001111
00000000 00000000 00000000 00000000 00001101 00001010 10010111 11101101
00111001 00000000 00000000 00000000 00000000 00000010 01010111 01010011
11011110 00000000 00000000 00000000 00000000 00010110 00001011 00101110
10010001 00000000 00000000 00000000 00000000 00100001 11100100 11000110
11111010 00000000 00000000 00000000 00000000 00100110 00011111 10001110
00000010
End of file reached successfully

Answer 2

fgetc的返回值是int类型。一个可能的解释是fgetc失败了，返回了-1，导致你换算后的二进制全是1。
把ch的声明改成int

 while( (ch = fgetc(fp)) != 255){

改为

 while( (ch = fgetc(fp)) != -1){

while之后打印一下errno：

printf("%d %s\n", errno, strerror(errno));

看到底是什么原因导致fgetc失败.