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cs50 - CS50 Recover 运行并恢复除第一个文件之外的所有文件

问题描述

我的问题是关于作为 CS50 一部分的恢复任务。

代码正在运行（最终），它生成了 50 个 JPEG 文件，其中大多数是正确的图像，除了第一个文件不是图像，因此它没有通过 check50。

我花了很长时间试图找出问题所在，但我无法确定它，所以我希望有人能够帮助我，这样我就可以继续前进。

提前致谢！这是我的代码：

    int main(int argc, char *argv[])
    {
    // ensure proper usage
    if (argc != 2)
    {
        fprintf(stderr, "Usage: Name of Memory Card File\n");
        return 1;
    }

    char *readfile = argv[1];

    // open memory card file
    FILE *card_ptr = fopen(readfile, "r");
    if (card_ptr == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", readfile);
        return 2;
    }

    //Declare a buffer to read into
    unsigned char *buffer = malloc(512);

    //to check if we have already found a file
    bool (jpgAlreadyNew) = false;

    //declare counter for the number of files found and a file pointer
    int filenumber = 0;
    FILE *new_jpg_ptr = NULL;
    char filename[8];

    //read in bytes until reach EOF
    while (fread(buffer, 1, 512, card_ptr) != 0x00)
    {
        //if we reach the header pattern of bytes
        if (buffer [0] == 0xff && buffer [1] == 0xd8 && buffer [2] == 0xff && (buffer [3] & 0xf0) == 0xe0)
        {

            //if there is not already a JPEG file found
            if (!jpgAlreadyNew)
            {
                //change the bool value
                (jpgAlreadyNew) = true;

                //open new file
                sprintf(filename, "%03i.jpg", filenumber);
                new_jpg_ptr = fopen(filename, "w");
                if (new_jpg_ptr == NULL)
                    {
                        return 3;
                    }
                //add to counter of files found
                filenumber++;

                //write files from buffer into new img file
                fwrite(buffer, 1, 512, new_jpg_ptr);

            }

            //if there is already a JPEG file found
            if (jpgAlreadyNew)

            {
                //close the previous file which would now be complete
                fclose(new_jpg_ptr);

                //open new file
                sprintf(filename, "%03i.jpg", filenumber);
                new_jpg_ptr = fopen(filename, "w");
                if (new_jpg_ptr == NULL)
                    {
                        return 4;
                    }
                //add to counter of files found
                filenumber++;

                //write files from buffer into new img file
                fwrite(buffer, 1, 512, new_jpg_ptr);

            }

        }

        // else if we do not see pattern of header bytes
        else
        {
            //if already found a jpg file which is open then write the bytes to that file
            if (jpgAlreadyNew)
              {
                  fwrite(buffer, 1, 512, new_jpg_ptr);
              }
            //if no file found yet, discard and move on
            if (!jpgAlreadyNew)
              {
                  continue;
              }
        }
    }

    //free memory
    free (buffer);

    //close pointers and end program successfully
    fclose(card_ptr);
    fclose(new_jpg_ptr);
    return 0;
}

标签： cs50

解决方案

让我们从找到第一个 jpeg 签名开始浏览程序：

这if (!jpgAlreadyNew)评估为真，因此它进入 if 块；它做的第一件事是(jpgAlreadyNew) = true;。完成创建文件并写入第一个块后，接下来会发生什么？这if (jpgAlreadyNew). 这也评估为真。所以它关闭 000.jpg 并继续移动。

由于jpgAlreadyNew是布尔值，因此if {} else {}构造就足够了。

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