Forum und email

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 af PHP har indbygget support for denne udvidelse. Du behøver ikke indsætte ekstra udvidelser for at bruge disse funktioner.

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

Runtime Konfiguration

Virkemåden af disse funktioner er berørt af indstillinger 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 flere detaljer og definationer af PHP_INI_* constanterne, se ini_set() dokumentation.

Her er en kort forklaring på konfigurations-direktiverne.

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().

Foruddefinerede Konstanter

Konstanterne nedenunder er defineret af denne udvidelse, og vil kun være tilgængelige når denne udvidelse enten er blevet kompileret ind i PHP eller dynamisk indsat under runtime.

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