cs50 pset4 recover.c 需要建议

Question

我可以使用来自 cs50 的关于此 pset 的一些指导。以下是我到目前为止的代码。我被困在这一点上，我不知道如何进行。当我运行程序输出 16 个 jpg 文件时，但我无法查看它们，所以一定是出了什么问题。欢迎任何提示。

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

int main(void)
{               
// create buffer to store in
unsigned char buffer[512];

// array for filename is 8 for "000.jpg"
char jpgName[8];

// declaring counter for amount of jpegs
int jpgcounter = 0;

// open memory card file
FILE* inptr = fopen("card.raw", "r");
FILE* outptr = NULL;

if (inptr == NULL)
{
    printf("Could not open %s.\n", "card.raw");
    return 1;
}   

    // repeat until end of card 
    while(fread(buffer, sizeof(buffer), 1, inptr) == 1)
    {                                   

        // find beginning of jpg
        if(buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] == 0xe0 || buffer[3] == 0xe1))
        {   
            // if allready a outptr file is open close it
            if (outptr != NULL)
            {
                    fclose(outptr);
            }

            // create filename for jpegs
            sprintf(jpgName,"%03d.jpg", jpgcounter);

            // open a new file with name defined by sprintf
            FILE* outptr = fopen(jpgName, "w");                             

            // write into the outfile from buffer
            fwrite(&buffer, sizeof(buffer), 1, outptr);

            // increment counter for jpegs
            jpgcounter++;
           }                                    
    }
    fclose(inptr);
    return 0;   
}

Answer 1

这行不通：

while(fread(buffer, sizeof(buffer), 1, inptr) == 1)
{                                   

    // read 512 bytes from inptr and store them in buffer
    fread(&buffer, sizeof(buffer) , 1, inptr);

当您使用 fread 两次时，第一次读取的数据会被第二次覆盖。看起来好像这丢失了原始文件中每个 kB 的前 512 个字节。

如果删除第二个 fread()，您应该会更进一步。

Answer 2

如果我对你的任务理解正确，你想要这样的东西——请看下面。提示：如果不是jpg文件开头你打算怎么办？

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

int main(void)
{               

unsigned char buffer[512] = {0};
char jpgName[8] = {0};
int jpgcounter = 0;
FILE* outptr = NULL;

// open memory card file
FILE* inptr = fopen("card.raw", "rb");
if (inptr == NULL)
{
    printf("Could not open %s.\n", "card.raw");
    return 1;
}   

// Start reading    
while(fread(buffer, sizeof(buffer), 1, inptr) == 1)
{                                   

        // Find beginning of jpg
        if(buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] == 0xe0 || buffer[3] == 0xe1))
        {   
            if(NULL!=outptr)                   
            {
              fclose(outptr);
              outptr=NULL;
            }

            // Create filename for jpegs
            sprintf(jpgName,"%03d.jpg", jpgcounter);

            // Open a new file with name defined by sprintf
            outptr = fopen(jpgName, "wb");         
            if (NULL == outptr)
            {
              printf("Could not open %s.\n", jpgName);
              return 1;
            }                     

            // Write into the outfile from buffer
            fwrite(buffer, sizeof(buffer), 1, outptr);

            // Increment counter for jpegs
            jpgcounter++;
         }
          else 
         {
             // Continue writing to old file if it is not beginning of file
             if(NULL!=outptr)
                fwrite(buffer, sizeof(buffer), 1, outptr);                              
         }   
    }

    if(NULL!=outptr)
      fclose(outptr);
    if(NULL!=inptr)
      fclose(inptr);

    return 0;   
}

cs50 pset4 recover.c 需要建议

cs50 pset4 recover.c need advice

c

cs50