PHP从结构的二进制文件提取数据

Question

我有我的文件与图像结构。我想从中提取数据到数组：

function get_data($file, $number) 
{ 
    if(!$fp = fopen ($file, 'rb')) return 0; 
    $fsize = filesize($file); 
    if(!$data = fread ($fp, $fsize)) return 0; 
    $data_format= 
     '@100/'. 
     'smember_id/'. 
     'cmember_name_length/'. 
     'a' . $member_name_length . 'member_name/'. 
     'C100other_data/'; 
    $data = unpack ($data_format, $data); 
    fclose($file); 
    return $data; 
} 

如何从文件中获取$ member_name_length？我想创建一个函数，如果用户输入$ number，它将返回一个$ number（th）数据的数组。

谢谢。

Answer 1

既然你有可变长度的数据块，就可以读取它们只能按顺序，所以为了读出第n个块，则需要阅读所有n个第一块：

function readDataBlock($f) { 
    $data = unpack('nmember_id', fread ($f, 2)); // I assume member_id is n, not s 
    if ($data['member_id'] == 0xFFFF) { 
     throw new \Exception('End of file'); 
    } 
    $data = array_merge($data, unpack('Cmember_name_length', fread ($f, 1))); //again, it must be C, not c, as I can't imagine negative length. 
    $data = array_merge($data, unpack('a*member_name', fread ($f, $data['member_name_length']))); // be sure you understand how a differs from A 
    return array_merge($data, unpack('C100other_data', fread ($f, 100))); // are you sure C100 is what you want here? 
} 


function get_data($file, $number) 
{ 
    if(!$fp = fopen ($file, 'rb')) return 0; 

    fread ($fp, 100); //skip header 

    for($n = 0; $n <= $number; $n++) { 
     $data = readDataBlock($fp); // read single member 
    } 

    fclose($fp); 
    return $data; //return the n-th member 
} 

如果文件是足够小，以适应内存，它可能会更好地阅读一次，并从内存返回第n个成员：

$data = []; 
while(true) { 
    try { 
     $data[] = readDataBlock($fp); 
    } catch(\Exception $e) { 
     break; 
    } 
} 


function get_data(&$data, $number) 
{ 
    return $data[$number]; 
}