So, php_ifx.dll is not more supported, because the PECL site warnings "This package is not maintained". I can't find the source-code to compile.
Best try is the PDO Informix.
为使 PHP 解析器支持 Informix 模块，需要在编译 PHP 时加入选项 --with-informix[=DIR] , 其中的 DIR 指的是 Informix 的安装目录（INFORMIXDIR）,默认是空。
So, php_ifx.dll is not more supported, because the PECL site warnings "This package is not maintained". I can't find the source-code to compile.
Best try is the PDO Informix.
For windows , apache server, php connect informix.
I have try 4 days and finally success with it.
My php env is apache 2.0, php 5.2, informix 09.40
1) download php_ifx.dll from php home page （search with pecl-5.2 Win32）, put php_ifx.dll in your php extension dir , in my case c:\php\ext .
2) in php.ini add follows :
extension=php_ifx.dll
3) download informix cdsk 3.0TC for windows from ibm, install it and then run your php app which has informix connect operation, if apache server has a error dialog, then restart computer(because installation add a system variable path : C:\Program Files\IBM\Informix\Client-SDK\bin), after restart confirm this error not occure again. (in this step php page finally error with "sqlstate = IX 000 sqlcode= -25560" because of informix server not set, we will solute it in next step)
4) run C:\Program Files\IBM\Informix\Client-SDK\bin\setnet32.exe change the values by following
4)-1 Tab Server Information
IBM Informix Server : informix server name
HostName : informix server ip address
Protocolname : onsoctcp
ServiceName : informix server port
4)-2 Host Information
Current Host : informix server ip address
then click OK
5) run your php app, then you can do any ifx_xxxxx informix db operation. (in windows apache env don't mind INFORMIXDIR var ect...)