c - C 中未遇到文件结尾 (eof)

Question

我正在尝试运行代码。除最后一张外，所有图像均按照规范正常运行。

前四个字节 (B) 重复如下:

b8 97 98 c5

未遇到文件结尾，因此发现最后一个图像已损坏。

编辑:

1. 已经提到文件中有 50 张图像。
2. 您可以从以下位置获取原始文件:http://cdn.cs50.net/2017/fall/psets/4/recover/card.raw

原代码如下:

// Recovers lost images (.jpeg) in a memory card

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

#define buffsize 10

// Function to check whether jpeg or not
int check_jpeg(unsigned char *argv) {
    unsigned int v1 = (int)argv[0];
    unsigned int v2 = (int)argv[1];
    unsigned int v3 = (int)argv[2];
    unsigned int v4 = (int)argv[3];
    if (v1 == 0xff && v2 == 0xd8 && v3 == 0xff) {
        switch (v4) {
          case 0xe0:
          case 0xe1:
          case 0xe2:
          case 0xe3:
          case 0xe4:
          case 0xe5:
          case 0xe6:
          case 0xe7:
          case 0xe9:
          case 0xea:
          case 0xeb:
          case 0xec:
          case 0xed:
          case 0xee:
          case 0xef:
            return 1;
            break;
          default:
            return 0;
        }
    } else {
        return 0;
    }
}

int main(int argc, char *argv[]) {
    // Cautioning the user for wrong usage
    if (argc != 2) {
        fprintf(stderr, "Usage: ./recover file\n");
        return 1;
    }

    // Opens the .raw file to begin inspection
    FILE *camera = fopen(argv[1], "r");

    // Checks the validity of the opened file
    if (camera == NULL) {
        fprintf(stderr, "Error opening file: %s\n",argv[1]);
        return 2;
    }

    int counter = 0; // Declaring and Initialising the counter
    int online = 0; // To know whether image is being written

    char *filename = (char*)malloc(buffsize);
    FILE *outptr;

    while (1) {
        unsigned char *image = malloc(512);
        if (image == NULL) {
            fprintf(stderr, "Error creating pointer \n");
            return 200;
        }
        fread(image, 512, 1, camera);
        if (image != NULL) {
            int flag = check_jpeg(image);
            if (counter == 50) {
                printf("%x %x %x %x\n", image[0], image[1], image[2], image[3]);
            }
            if (flag == 1) {
                if (counter != 0) {
                    fclose(outptr);
                }
                counter++;

                // Creating the output file pointer
                snprintf(filename, buffsize - 1, "%03i.jpg", counter);
                outptr = fopen(filename, "w");
                if (outptr == NULL) {
                    fprintf(stderr, "Error opening file: %s\n", filename);
                    return 201;
                }

                // Writing to the file
                fwrite(image, 512, 1, outptr);
                online = 1;
            } else
            if (flag == 0 && online == 1) {
                fwrite(image, 512, 1, outptr); // Continue writing to the output file
            }
            free(image);
        } else {
            fclose(camera);
            fclose(outptr);
            return 0;
        }
    }
}

Answer 1

您的代码中存在多个问题:

• 您没有检查fread成功读取了多少数据。在文件末尾，fread 返回 0，否则 fread 返回成功读入目标数组的 block 数。要跟踪读取的字节，请传递 1 作为 block 大小，并传递 512 作为 block 数。
• 没有真正需要分配文件名和输入/输出缓冲区，本地数组就可以满足您的目的。
• 文件应以二进制模式打开:FILE *camera = fopen(argv[1], "rb");
• snprintf 的第二个参数应该是缓冲区大小，而不是要写入的最大字符数:snprintf(filename, buffsize, "%03i.jpg", counter);