改进 C 代码以删除复制粘贴

Question

P.S。有些人在理解问题 'how to improve my code' 时遇到了问题。我再清楚不过了，真的。我同时解决了这个问题。

我正在完成一项任务，通过首先通过 'magic numbers' 找到它们来从 CD 卡文件 (.raw) 中恢复照片。如果有人知道它是什么，它是 CS50 class 的一部分。

无论如何，它似乎工作正常。我可以恢复所有照片，但其中一些质量较差，然后是其他照片（很多白色像素）- 不确定是否有意。

在代码中，我根据条件打开和关闭 jpg 文件以将信息写入其中。我想不出一种方法来避免复制粘贴到 fopen、fwrite 和 fclose 文件。我想改进这部分。这是代码：

typedef uint8_t BYTE;

int main(void)
{
    // open input file 
    FILE* card_file = fopen("card.raw", "r");
    if (card_file == NULL)
    {
        printf("Could not open card.raw\n");
        return 1;
    }

// declare output file
FILE* image;

// array to store values we read for each 512 bytes
BYTE buffer[512];

// number of jpg files found
int jpgs = 0;

// variable used to create new files
char title[10];

// execute until the end of file is reached
while(fread(&buffer, sizeof(BYTE), 512, card_file) > 0)
{
    // find a new jpg file by its magic numbers
    if((buffer[0] == 0xff) && (buffer[1] == 0xd8) && (buffer[2] == 0xff))
    {
        //create a new file if it's found
        sprintf(title, "%03d.jpg", jpgs);
        jpgs++;

        //open the file and check if file is opened correctly
        image = fopen(title, "a");

        if (image == NULL)
        {
            fprintf(stderr, "Could not create %03d.jpg\n", jpgs);
            return 2;
        }

        // write into the file and close it
        fwrite(&buffer, sizeof(BYTE), 512, image);
        fclose(image);
    }
    else 
    {
        //check if a jpg file was already found before
        if(jpgs > 0)
        {
            //open the file and check if file is opened correctly
            image = fopen(title, "a");

            if (image == NULL)
            {
                fprintf(stderr, "Could not create %03d.jpg\n", jpgs);
                return 2;
            }

            // write into the file and close it
            fwrite(&buffer, sizeof(BYTE), 512, image);
            fclose(image);
        }
    }
}

//close the input file
fclose(card_file);

}

我试图创建一个单独的函数，但无法弄清楚如何处理指向我需要传递给它的整数值的指针。

如有任何帮助，我们将不胜感激。

Answer 1

唯一需要通过引用传递的是 title 和 buffer，您需要 return 我们可以测试的布尔值以允许 return 2; 在来电者上。

int appendBuffer(char *title, BYTE *buffer)
{
    //open the file and check if file is opened correctly
    FILE* image = fopen(title, "a");

    if (image == NULL)
    {
        fprintf(stderr, "Could not open %s\n", title); //note reuse of title now
        return 0; //it didn't work
    }

    // write into the file and close it
    fwrite(buffer, sizeof(BYTE), 512, image);
    fclose(image);
    return 1; //it worked
}

用法：

// find a new jpg file by its magic numbers
if((buffer[0] == 0xff) && (buffer[1] == 0xd8) && (buffer[2] == 0xff))
{
    //create a new file if it's found
    sprintf(title, "%03d.jpg", jpgs);
    jpgs++;

    if (!appendBuffer(title, buffer)) return 2;
}
else 
{
    //check if a jpg file was already found before
    if(jpgs > 0)
    {
       if (!appendBuffer(title, buffer)) return 2;
    }
}

另一个比较许多连续字节的想法，使用 memcmp 而不是 && 链：

const char magic[] = {0xff, 0xd8, 0xff};

// find a new jpg file by its magic numbers
if (memcmp(buffer, magic, 3) == 0)

改进 C 代码以删除复制粘贴

Improving C code to remove copy-paste

c

cs50