Zlib 函数
在线手册：中文 英文
PHP手册

gzuncompress

(PHP 4 >= 4.0.1, PHP 5)

gzuncompress — Uncompress a compressed string

说明

string gzuncompress ( string $data [, int $length = 0 ] )

This function uncompress a compressed string.

参数

data

The data compressed by gzcompress().

length

The maximum length of data to decode.

返回值

The original uncompressed data or FALSE on error.

The function will return an error if the uncompressed data is more than 32768 times the length of the compressed input data or more than the optional parameter length.

范例

Example #1 gzuncompress() example

<?php
$compressed   = gzcompress('Compress me', 9);
$uncompressed = gzuncompress($compressed);
echo $uncompressed;
?>

参见

Zlib 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: Uncompress a compressed string

用户评论:

MagicalTux at php dot net (31-Dec-2010 09:36)

Hi, I got an alternative for those zipped strings that gzuncompress() cannot extract.

It is a bit better than previous options as it do not create any temporary files, but it has to encode the string in base64, meaning it won't be as fast as a native equivalent (which is probably going to be gzdecode())

<?php
if (!function_exists('gzdecode')) {
    function gzdecode($string) { // no support for 2nd argument
        return file_get_contents('compress.zlib://data:who/cares;base64,'. base64_encode($string));
    }
}
?>

squeegee (24-Aug-2009 03:07)

One way to uncompress zlib-compressed data that is in a file without first reading in the file and then gzuncompressing it (maybe you have memory problems doing it that way) is to compile the zpipe.c program from zlib ( http://www.zlib.net/zpipe.c )...

on linux, etc:

# gcc -lz -o zpipe zpipe.c

# cp zpipe /usr/local/bin

Then do this

<?php

$uncompressed = shell_exec("cat $compressed_file | zpipe -d");

?>

heavyccasey at gmail dot com (08-Nov-2007 04:30)

Note that gzuncompress() may not decompress some compressed strings and return a Data Error.

The problem could be that the outside compressed string has a CRC32 checksum at the end of the file instead of Adler-32, like PHP expects.

Workaround:
<?php
    function gzuncompress_crc32($data) {
         $f = tempnam('/tmp', 'gz_fix');
         file_put_contents($f, "\x1f\x8b\x08\x00\x00\x00\x00\x00" . $data);
         return file_get_contents('compress.zlib://' . $f);
    }
?>

gabriel at bumpt dot n-et (17-Sep-2007 11:08)

To uncompress in PHP a string that has been compressed using MySQL's COMPRESS() function, you need to discard the first four bytes of the binary data:

<?php

  /*
   * Example:
   *
   * insert into mytable (myfield, ...) values (COMPRESS('foobar'), ...)
   *
   * then:
   */
$compressed = //...select myfield from mytable where...
  /*
   * then:
   */
$uncompressed = gzuncompress(substr($compressed, 4));
?>

Of course, you can use MySQL's UNCOMPRESS() function.
I was just providing an alternate method.

emanuele at fondani dot it (25-Nov-2006 11:21)

Note that the manual states that the input parameter must be a string compressed with gzcompress(), so it is not guaranteed that it will compress ANY zlib compressed string.
I realized this while decompressing some compressed string in a pdf file. The gzuncompress() function produces a data error, but the string can be successfully decompressed with other zlib decompressors.

More info here:
http://bugs.php.net/?id=39616

chappy at citromail dot hu (13-Apr-2006 03:47)

Reading an ID3v2.3+ tag it is versy useful, because these tag's frames might be compressed. Zlib compressed frame layout (ID3v2.3):

Descriptior                                                    Size
-------------------
Frameheader:
Frame id:                                                      4 bytes
Frame size (full frame size - frameheader size): 4 bytes
Frame flags:                                                  2 bytes
    The 2nd byte's 7th bit must be 1 (e.g.: %1xy00000)
Frame content decrompessed size:                   4 bytes
--------------------
Framecontent:
Compressed string                                          described in 'frame size'

<?php
$frame="[read from a mp3 file]";
$frame_id=substr($frame,0,4);
/*....*/
$cs=substr($frame,10,4);
$checksize=$cs[3]*16777216+$cs[2]*65536+$cs[1]*256+$cs[0];

$content=substr($frame,14,$contentsize);
$content=gzuncompress($content);
if(strlen($content)!=$checksize){
    echo 'Error whil uncrompessing frame data<br>';
}
echo $content;
?>