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Zlib Compression Functions


This module enables you to transparently read and write gzip (.gz) compressed files, through versions of most of the filesystem functions which work with gzip-compressed files (and uncompressed files, too, but not with sockets).

Note: Version 4.0.4 introduced a fopen-wrapper for .gz-files, so that you can use a special zlib: URL to access compressed files transparently using the normal f*() file access functions if you prefix the filename or path with zlib: when calling fopen(). This feature requires a C runtime library that provides the fopencookie() function. Up to now the GNU libc seems to be the only library that provides this feature.
In PHP 4.3.0, zlib: has been changed to compress.zlib:// to prevent ambiguities with filenames containing ':' characters. The fopencookie() function is not longer required. More information is available in the section about Compression Streams.


This module uses the functions of » zlib by Jean-loup Gailly and Mark Adler. You have to use a zlib version >= 1.0.9 with this module.


Zlib support in PHP is not enabled by default. You will need to configure PHP --with-zlib[=DIR]

Windows-versionen av PHP har inbyggt stöd för det här tillägget. Du behöver inte ladda några ytterligare tillägg för att använda dessa funktioner.

Note: Built-in support for zlib on Windows is available with PHP 4.3.0.

Konfiguration under drift

De här funktionernas beteende påverkas av inställningarna i php.ini.

The zlib extension offers the option to transparently compress your pages on-the-fly, if the requesting browser supports this. Therefore there are three options in the configuration file php.ini.

Zlib Configuration Options
Name Default Changeable Changelog
zlib.output_compression "0" PHP_INI_ALL Available since PHP 4.0.5.
zlib.output_compression_level "-1" PHP_INI_ALL Available since PHP 4.3.0.
zlib.output_handler "" PHP_INI_ALL Available since PHP 4.3.0.
For further details and definitions of the PHP_INI_* constants, see the php.ini directives.

Här följer en kort förklaring av konfigurationsdirektiven.

zlib.output_compression boolean/integer

Whether to transparently compress pages. If this option is set to "On" in php.ini or the Apache configuration, pages are compressed if the browser sends an "Accept-Encoding: gzip" or "deflate" header. "Content-Encoding: gzip" (respectively "deflate") and "Vary: Accept-Encoding" headers are added to the output. In runtime, it can be set only before sending any output.

This option also accepts integer values instead of boolean "On"/"Off", using this you can set the output buffer size (default is 4KB).

Note: output_handler must be empty if this is set 'On' ! Instead you must use zlib.output_handler.

zlib.output_compression_level integer

Compression level used for transparent output compression.

zlib.output_handler string

You cannot specify additional output handlers if zlib.output_compression is activated here. This setting does the same as output_handler but in a different order.


This extension defines a file pointer resource returned by gzopen().

Fördefinerade konstanter

Konstanterna nedan defineras av den här utbyggnaden, och kommer bara vara tillgängliga då utbyggnaden kompilerats med PHP eller laddats dynamiskt.

FORCE_GZIP (integer)


This example opens a temporary file and writes a test string to it, then it prints out the content of this file twice.

Example#1 Small Zlib Example


tempnam('/tmp''zlibtest') . '.gz';
$s "Only a test, test, test, test, test, test, test, test!\n";

// open file for writing with maximum compression
$zp gzopen($filename"w9");

// write string to file

// close file

// open file for reading
$zp gzopen($filename"r");

// read 3 char
echo gzread($zp3);

// output until end of the file and close it.


// open file and print content (the 2nd time).
if (readgzfile($filename) != strlen($s)) {
"Error with zlib functions!";


Table of Contents

  • gzclose — Close an open gz-file pointer
  • gzcompress — Compress a string
  • gzdecode — Decodes a gzip compressed string
  • gzdeflate — Deflate a string
  • gzencode — Create a gzip compressed string
  • gzeof — Test for end-of-file on a gz-file pointer
  • gzfile — Read entire gz-file into an array
  • gzgetc — Get character from gz-file pointer
  • gzgets — Get line from file pointer
  • gzgetss — Get line from gz-file pointer and strip HTML tags
  • gzinflate — Inflate a deflated string
  • gzopen — Open gz-file
  • gzpassthru — Output all remaining data on a gz-file pointer
  • gzputs — Alias of gzwrite
  • gzread — Binary-safe gz-file read
  • gzrewind — Rewind the position of a gz-file pointer
  • gzseek — Seek on a gz-file pointer
  • gztell — Tell gz-file pointer read/write position
  • gzuncompress — Uncompress a compressed string
  • gzwrite — Binary-safe gz-file write
  • readgzfile — Output a gz-file
  • zlib_get_coding_type — Returns the coding type used for output compression