使用feof函数退出文件

Question

我正在尝试让一个照片提取程序在检测到它位于要提取的文件的末尾时停止。我通过设置一个if条件来做到这一点：

if (feof(file))
{
   return 2;
}

在fread函数之后：

fread(array, 1, 512, file);

因此，如果fread读到文件的末尾，那么feof将触发，从而结束程序。这是我的代码：

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

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        printf("Invalid entry.\n");
        return 0;
    }

    int counter = 1;
    FILE* images;
    char jpg_name[8];

    // Check if bytes are jpg. signatures.
    for (int n = 0; counter < 51; n = n + 512)
    {
        // Open file for reading.
        FILE *file = fopen(argv[1], "r");
        if (!file)
        {
            return 1;
        }

        unsigned char array[512];
        fseek(file, n, SEEK_SET);
        fread(array, 1, 512, file); // if EOF, won't have 512 to write into!!!
        if (feof(file))
        {
            return 2;
        }
        fclose(file);

        if (array[0] == 0xff && array[1] == 0xd8 && array[2] == 0xff && (array[3] & 0xf0) == 0xe0)
        {
            // Convert integer to string and store into jpg character array. Increment image number.
            sprintf(jpg_name, "%03i.jpg", counter);
            counter++;

            // Open images file to write into, allocate memory to jpg file to write into, write 512 bytes from array into image file.
            images = fopen(jpg_name, "a");
            fwrite(array, 1, 512, images);
            fclose(images);
        }
        else // If 1st 4 bytes aren't jpg signature.
        {
            if (counter > 1)
            {
                images = fopen(jpg_name, "a");
                fwrite(array, 1, 512, images);
                fclose(images);
            }
        }
    }
}

我还尝试了放置条件：

if (fread(array, 1, 512, file) == 512)

使其在读取少于512字节后停止运行，以自动停止程序，但这似乎也不起作用。

任何澄清或建议都将不胜感激，谢谢！

Answer 1

不要每次在循环中打开和关闭文件。只需以512块的形式读取文件，直到它到达EOF。

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

#define SIZE 512

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        printf("Invalid entry.\n");
        return 0;
    }

    int counter = 1;
    FILE* images;
    char jpg_name[8];

    // Open file for reading.
    FILE *file = fopen(argv[1], "r");
    if (!file)
    {
        return 1;
    }

    unsigned char array[SIZE];

    // Check if bytes are jpg. signatures.
    while (fread(array, 1, SIZE, file) == 1)
    {
        if (array[0] == 0xff && array[1] == 0xd8 && array[2] == 0xff && (array[3] & 0xf0) == 0xe0)
        {
            // Convert integer to string and store into jpg character array. Increment image number.
            sprintf(jpg_name, "%03i.jpg", counter);
            counter++;

            // Open images file to write into, allocate memory to jpg file to write into, write 512 bytes from array into image file.
            images = fopen(jpg_name, "a");
            fwrite(array, 1, 512, images);
            fclose(images);
        }
        else // If 1st 4 bytes aren't jpg signature.
        {
            if (counter > 1)
            {
                images = fopen(jpg_name, "a");
                fwrite(array, 1, 512, images);
                fclose(images);
            }
        }
    }
    fclose(file);
}