c++ - 使用CPP获取dd图像的十六进制值

Question

我想读取前4096个字节作为图像文件的十六进制(来自dd加密设备的luks)。因此，我首先使用unsigned long进行了测试，其值范围从0 to 18446744073709551615开始。但是用这个代码

int main() {
    unsigned long c;

    FILE *fp = fopen("C:\\image.dd", "r");
    if (fp == NULL) {
        fprintf(stderr, "Can't read file");
        return 0;
    }

     while (!feof(fp)){                         // while not end of file
           c=fgetc(fp);                         // get a character/byte from the file
           printf("%02x ",c);                   // and show it in hex format
    }
    fclose(fp);

    return 0;
} 

我将得到以下输出:

4c 55 4b 53 ba be 00 01 61 65 73 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 74 73 2d 70 6c 61 69 6e 36 34 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 73 68 61 32 35 36 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 00 00 00 00 40 31 ea 2e 93 28 55 cd 52 b6 c4 51 1e 0f b1 25 0e 2d 65 72 85 f2 41 97 b3 9b 76 ae 07 e5 53 ac 02 21 b4 ffffffff

我的 image.dd的前512个字节如下所示:

4C 55 4B 53 BA BE 00 01 61 65 73 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 78 74 73 2D 70 6C 61 69 
6E 36 34 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 73 68 61 32 35 36 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 10 00 00 00 00 40 
31 EA 2E 93 28 55 CD 52 B6 C4 51 1E 0F B1 25 0E 
2D 65 72 85 F2 41 97 B3 9B 76 AE 07 E5 53 AC 02 
21 B4 1A 6F 0C 8D E2 08 62 91 4D 22 3D CA A2 51 
19 0A 74 29 00 01 06 4B 32 38 38 33 34 64 34 66 
2D 36 62 32 64 2D 34 37 33 62 2D 62 34 63 65 2D 
33 31 38 32 36 65 64 61 65 39 63 39 00 00 00 00 
00 AC 71 F3 00 10 64 B8 37 E9 07 F3 84 51 CF 51 
23 E8 F2 8E 31 57 FE 2C DE D5 70 76 F2 1B B0 F8 
95 33 A6 BB E4 4F 91 A8 00 00 00 08 00 00 0F A0 
00 00 DE AD 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 02 00 00 00 0F A0 
00 00 DE AD 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 03 F8 00 00 0F A0 
00 00 DE AD 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 05 F0 00 00 0F A0 
00 00 DE AD 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 07 E8 00 00 0F A0 
00 00 DE AD 00 00 00 00 00 00 00 00 00 00 00 00

所以这很奇怪。为什么要这样做呢？现在为什么要用 unsigned long以及值 ffffffff呢？
编辑:我只是想像，那就是我是否使用 unsigned long或类似 unsigned int。但是问题是一样的。

Answer 1

您有四个错误。
首先，您在打印数据时不会检查读取是否成功。
检查应该在c=fgetc(fp);和printf("%02x ",c);之间
其次，您将错误的类型传递给printf()并调用未定义的行为。
格式%02X需要unsigned int。 (根据this answer，在适当范围内的int也可以)
第三，以文本模式打开二进制文件。
因此，在0x1A(EOF)字节处停止读取。
要通过fopen()以二进制模式打开文件，应将b添加到模式字符串中。
第四，您不将读取限制为前4096个字节。
请注意， fgetc() 返回int，因此使用unsigned long是多余的。
固定代码:

#include <stdio.h>

int main() {
    int i; // read size counter
    int c; // use proper type

    FILE *fp = fopen("C:\\image.dd", "rb");     // open file in binary mode
    if (fp == NULL) {
        fprintf(stderr, "Can't read file");
        return 0;
    }

    for (i = 0; i < 4096; i++) {                // while not end of size to read
           c=fgetc(fp);                         // get a character/byte from the file
           if (c == EOF) break;                 // stop at end of file
           printf("%02x ",c);                   // and show it in hex format
    }
    fclose(fp);

    return 0;
}