Question

我遵循pset 3 restore的伪代码，我的代码仅输出一个图像，并且在number = fread(buffer, 1, 512, file);行中第4次循环后，调试器（debug50）退出。

我检查了输出jpeg的十六进制值，发现与原始文件相比，它也是不正确的。我可以辨认出图像，但有些十六进制数偏离很小。I

// open card file 
FILE *file = fopen(argv[1], "r");
if (file == NULL)
{
    fprintf(stderr, "Couldn't open %s", argv[1]);
    return 2;
}

// buffer
unsigned char *buffer = malloc(513);
buffer[512] = 0x00;

// number
int number = 512;

// bool
int jpegFound = 0;

// jpeg number
int jpegNum = 0;

// jpeg name  
char *jpegName = malloc(8);
jpegName[7] = 0x00; 

// jpeg file pointer
FILE *jpegPtr;

// iterate through all the blocks of the card
while (1)
{
    // read 512 bytes into a buffer
    number = fread(buffer, 1, 512, file);

    // break out of the loop if its the EOF
    if (number != 512)
    {
        break;
    }

    // check whether its the start of a new jpeg
    if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
    {
        // have we already found a jpeg?
        if (jpegFound == 1)
        {
            // close previous jpeg file
            fclose(jpegPtr);

            // store the jpegName in a string
            sprintf(jpegName, "%03i.jpg", jpegNum);

            // open a new file with the stored jpeg name
            jpegPtr = fopen(jpegName, "w");

        }
        else
        {
            // we found a jpeg finally
            jpegFound = 1;

            // store the jpeg Name in a string
            sprintf(jpegName, "%03i.jpg", jpegNum);

            // open a new file with the stored jpeg name
            jpegPtr = fopen(jpegName, "w");
        }

        // write buffer to the jpeg
        fwrite(buffer, 1, 512, jpegPtr);
    }
    else
    {
        if (jpegFound == 1)
        {
            // these bytes are part of the previous jpeg
            fwrite(buffer, 1, 512, jpegPtr);
        }
        else
        {
            // this means that these bytes can be discarded
        }
    }
}

// close any remaining files
fclose(jpegPtr);

// free the memory we used in malloc
free(buffer);
free(jpegName);

// return 0
return 0;

./recover card.raw的输出预计会是很多图像，但只能得到一张看起来还不错的图像，但其十六进制值有些偏离。

Answer 1

我修复了它。我也没有增加jpegNum，就debug50而言，我仍然不知道是什么导致它退出。

pset 3-恢复-代码仅输出一个图像并调试50次退出

1 个答案: