使用 feof 函数退出文件

Question

我试图让照片提取程序在检测到它位于要提取的文件末尾时停止。我通过放置一个 if 条件来做到这一点：

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

fread 函数后：

fread(array, 1, 512, file);

这样如果fread读到文件末尾，feof就会触发从而结束程序。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);
            }
        }
    }
}

我也试过放置条件：

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

进入程序使其停止运行读取不到512字节后自动停止程序，不过这个好像也行不通

任何澄清或建议将不胜感激，谢谢！

Answer 1

不要每次都通过循环打开和关闭文件。以 512 为单位读取文件，直到达到 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);
}

使用 feof 函数退出文件

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