Including Files : Advanced
Sun, 22 January, 2006 – 11:02 am
Before I touched on one of the most useful basic benefit of using PHP and that was removing code that is repeated in a web site, placing it in its own file and just including it into your page using the include() function.
There are 3 further functions that do similar operations however also have their own use.
require() – this is virtually the same as include(). You use it in the same manner however the difference and possible benefit is that when a file is called using include, which doesn't exist, a warning is stated on the page (unless it is supressed) but the page continues to execute the remaining code. However when you call a non existent file using the require() function then this causes a fatal error on the page and terminates the script.
include_once() – this does as it says, it includes the file once. If you have already included the file before then when you use this function on a file it will not include it a second time.
require_once() – a combination of the two descriptions above. If the file does not exist it will call a fatal error and terminate the script however if the file has already been required before then it will not be executed a second time.
These functions have a lot of more advanced uses which I'll look at as time goes on but for now a simple rule of thumb is, if the content of an include file should only be run once, use require_once() or include_once(). Which one you use is personal preference although it's recommended to use require() where ever possible, I personally use include() unless I really want to kill a script!
A good example of using these is when you have your database connection details in an include file, so that you only have one real instance of them to update if/when you move servers. Unless you close your connection midway through your code (not recommended) then you cannot open a connection to the database for a second time. By using the include_once() function you can be sure that after the first call to the connection file, no subsequent calls will be executed.
I'll be getting onto databases soon 
No Responses to “Including Files : Advanced”