c - Fwrite 到位图文件导致无限循环

Question

我正在尝试用 C 语言为位图文件编写一个图像颜色逆变器。我在这里查看了类似的问题，但没有一个答案有效。 infinite loop in while loop

这是我陷入困境的 while 循环:

while(!feof(f))
{
    //stride = 4 * ((width * bytesPerPixel + 3) / 4);
    fread(&pix, sizeof(struct pixel),1, f); // put pixels into struct

    pix.blue = ~pix.blue;
    pix.green = ~pix.green;
    pix.red = ~pix.red;

    fseek(f, -sizeof(struct pixel) , SEEK_CUR);
    fwrite(&pix, sizeof(struct pixel),1, f);
    fseek(f, 0, SEEK_CUR);
}

这是我的其余代码:

int main(){
FILE *f;

f = fopen("penguin.bmp", "rb+");

struct bmp_header bmphead;
fread(&bmphead, sizeof(struct bmp_header), 1, f);

struct dib_header dibhead;
fread(&dibhead, sizeof(struct dib_header), 1, f);

if (dibhead.size != 40 || dibhead.bpp != 24){
    printf("Error. File format not supported.");
    return EXIT_FAILURE;
}

fseek(f, bmphead.offset, SEEK_SET); // Get to start of pixels
struct pixel pix;
while(!feof(f))
{
    //stride = 4 * ((width * bytesPerPixel + 3) / 4);
    fread(&pix, sizeof(struct pixel),1, f); // put pixels into struct

    pix.blue = ~pix.blue;
    pix.green = ~pix.green;
    pix.red = ~pix.red;

    fseek(f, -sizeof(struct pixel) , SEEK_CUR);
    fwrite(&pix, sizeof(struct pixel),1, f);
    fseek(f, 0, SEEK_CUR);
}

fclose(f);
return EXIT_SUCCESS;
}

Answer 1

由于 fwrite() 和 fseek() 清除了 EOF 标志，因此出现无限循环。您需要检查 fread() 是否成功，而不是检查 feof(f)。

while (fread(&pix, sizeof(struct pixel),1, f)) {
    pix.blue = ~pix.blue;
    pix.green = ~pix.green;
    pix.red = ~pix.red;

    fseek(f, -sizeof(struct pixel) , SEEK_CUR);
    fwrite(&pix, sizeof(struct pixel),1, f);
    fseek(f, 0, SEEK_CUR);
}