How to Config PHP to run snmp in php script?

Dear All, I am using RedHat Linux 7.2, PHP4.1 and its buitd-in apache, I had tested that the php run correctly with apache. According to the documentation of www.php.net, As shown below: ############################################# XCIII. SNMP functions In order to use the SNMP functions on Unix you need to install the UCD SNMP package. On Windows these functions are only available on NT and not on Win95/98. Important: In order to use the UCD SNMP package, you need to define NO_ZEROLENGTH_COMMUNITY to 1 before compiling it. After configuring UCD SNMP, edit config.h and search for NO_ZEROLENGTH_COMMUNITY. Uncomment the #define line. It should look like this afterwards: #define NO_ZEROLENGTH_COMMUNITY 1 If you see strange segmentation faults in combination with SNMP commands, you did not follow the above instructions. If you do not want to recompile UCD SNMP, you can compile PHP with the --enable-ucd-snmp-hack switch which will work around the misfeature. #################################################### I had successfully complie PHP with the --enable-ucd-snmp-hack switch but I can not find the file called "config.h" to edit. Finally, My question is WHERE is the file?? and IS THERE any points/steps need to look at in order to configure PHP to run snmp in PHP script?? Thx All.