PHP gzseek() Function: Usage and Examples

Use gzseek() when you need to moves a gzip stream pointer to an uncompressed-byte offset in a PHP application. The examples below show the actual operation and its limitations.

What Is gzseek() in PHP?

Moves a gzip stream pointer to an uncompressed-byte offset. The exact signature supported by your installation depends on its PHP version and enabled extensions.

Its syntax is:

gzseek($stream, int $offset, int $whence = ...): int

Parameters and return value: The parameter types, optional arguments, references, and return type are shown in the signature above. Optional parameters are marked with an ellipsis in this reference signature.

Example 1: Basic Usage

<?php

$path = tempnam(sys_get_temp_dir(),"gzip_"); $file = gzopen($path,"wb"); gzwrite($file,"ABCDE"); gzclose($file); $file = gzopen($path,"rb"); gzseek($file,2); echo gzread($file,3); gzclose($file); unlink($path);

Output:

CDE

Example 2: Different Input or Behavior

<?php

$path = tempnam(sys_get_temp_dir(),"gzip_"); $file = gzopen($path,"wb"); gzwrite($file,"012345"); gzclose($file); $file = gzopen($path,"rb"); gzseek($file,4); echo gzgetc($file); gzclose($file); unlink($path);

Output:

4

Practical Example: Applying the Function

<?php

$path = tempnam(sys_get_temp_dir(),"gzip_"); $file = gzopen($path,"wb"); gzwrite($file,"header:payload"); gzclose($file); $file = gzopen($path,"rb"); gzseek($file,7); echo gzread($file,20); gzclose($file); unlink($path);

Output:

payload

Important Behavior and Edge Cases

Seeking within compressed streams may require decompression and can be relatively slow.

Comparison With Related Functions

Common Beginner Mistakes

Key Takeaways

• Moves a gzip stream pointer to an uncompressed-byte offset.
• Seeking within compressed streams may require decompression and can be relatively slow.
• gztell() reports the current uncompressed offset; gzseek() changes it.

Use gzseek() for the specific operation demonstrated above. Check its prerequisites and handle failure conditions before using it with production data.