I am presuming every modern host company gives use of php5 (and that i observed that lots of have both 4 and 5) however WHICH php5 is most widely used... let us say i am trying to choose from curl copy handle and curl setopt array (during my previous question)... but curl setopt array will come in php 5.1.3 while curl copy handle will come in earlier versions... now how do you determine if it's worthwile to make use of factor that actually works with more recent version? How do you determine if php 5.1.3 can be used broadly enough? I am attempting to make my application operate on most designs available.

Make use of the function_is available approach to look for which function is available, then use that certain. This way it's not necessary to be worried about which version of PHP has been used. It is the same idea because the feature-recognition versus browser-recognition debate in javascript.

Based on this website, typically the most popular version of PHP on May 9, 2008 (more than a year ago) was PHP 5.2.5. So, you'd most likely be OK using 5.1.3 + features.

Besides what tj111 pointed out, the PHP version does not really mean which functions will or won't be available. Many hosts, specifically free hosts, disable features like cURL, mail(), ZipArchive, image* functions, system(), professional(), passthru() etc. If you wish to look for dependences, its suggested to check on for exactly the thing you need with function_is available().