为什么不能像unpack("Lfffffff",$bytes)那样把很多条unpack语句压缩成一条？

Question

<?php
//it is unnecessary to get the data file.
    $handle = fopen('data', 'rb');
    fread($handle,"64");
//it is no use to parse the first 64 bytes here.
    $bytes= fread($handle,"4");
    print_r(unpack("L",$bytes));
    echo  "<br/>";
    $bytes= fread($handle,"4");
    print_r(unpack("f",$bytes));
    echo  "<br/>";
    $bytes= fread($handle,"4");
    print_r(unpack("f",$bytes));
    echo  "<br/>";
    $bytes= fread($handle,"4");
    print_r(unpack("f",$bytes));
    echo  "<br/>";
    $bytes= fread($handle,"4");
    print_r(unpack("f",$bytes));
    echo  "<br/>";
    $bytes= fread($handle,"4");
    print_r(unpack("f",$bytes));
    echo  "<br/>";
    $bytes= fread($handle,"4");
    print_r(unpack("f",$bytes));
    echo  "<br/>";
    $bytes= fread($handle,"4");
    print_r(unpack("f",$bytes));
    echo  "<br/>";
?>

我用代码得到了正确的输出。

Array ( [1] => 20150416 )
Array ( [1] => 1.0499999523163 )
Array ( [1] => 1.25 )
Array ( [1] => 1.0299999713898 )
Array ( [1] => 1.1900000572205 )
Array ( [1] => 509427008 )
Array ( [1] => 566125248 )
Array ( [1] => 509427008 )

现在想把很多unpack语句压缩成unpack("Lfffffff",$bytes)形式，代码如下

<?php
    $handle = fopen('data', 'rb');
    fread($handle,"64");
    //it is no use to parse the first 64 bytes here.
    $bytes= fread($handle,"32");
    print_r(unpack("Lfffffff",$bytes));
?>

为什么我的结果中只有一个输出，没有其他已解析的数据？如何解决？

Array ( [fffffff] => 20150416 )

数据文件是用notepad++打开的，通过插件--TextFX查看。这里只解析了96个字节，fread省略了前64个字节。

Answer 1

来自unpack doc：

The unpacked data is stored in an associative array. To accomplish this you have to name the different format codes and separate them by a slash /. If a repeater argument is present, then each of the array keys will have a sequence number behind the given name.

试试这个例子：

<?php

$array = array (20150416, 1.0499999523163, 1.25, 1.0299999713898, 1.1900000572205, 509427008, 566125248, 509427008);

$output = pack('L', $array[0]);

for($i = 1; $i < 8; $i++) {
    $output .= pack('f', $array[$i]);
}   

print_r(unpack("LL/f7", $output));

?>

在unpack("LL/f7", $output)中第一个L指向unsigned long第二个L指向数组中的索引（见第一个元素在输出中）/（阅读答案的第一部分）和 f 指的是 float，7 指的是七个浮点值。

输出：

Array
(
    [L] => 20150416
    [1] => 1.0499999523163
    [2] => 1.25
    [3] => 1.0299999713898
    [4] => 1.1900000572205
    [5] => 509427008
    [6] => 566125248
    [7] => 509427008
)

你的情况应该是：

<?php
    $handle = fopen('data', 'rb');
    $bytes= fread($handle,"32");
    print_r(unpack("LL/f7",$bytes));
?>

为什么不能像unpack("Lfffffff",$bytes)那样把很多条unpack语句压缩成一条？

Why can't compress many unpack statements into one as the form of unpack("Lfffffff",$bytes)?

php

arrays

binaryfiles

file

unpack