将 bytes 转为可读的单位

char* readable_fs(double size/*in bytes*/, char *buf) {
    int i = 0;
    const char* units[] = {"B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"};
    while (size > 1024) {
        size /= 1024;
        i++;
    }
    sprintf(buf, "%.*f %s", i, size, units[i]);
    return buf;
}

// usage
struct stat info;
char buf[10];
lstat("somefile.txt", &info);
printf("File size: %s\n", readable_fs(info.st_size, buf));

sprintf(buf, "%.*f %s", i, size, units[i]);