The base difference between the “include()” and “require()” is that the “require()” give the fatal error and halt the execution of the program when the required pages are not available.
The “include()” function only gives the warning message and continue the execution of the program even the required pages is not found or available .
The various way to include the file to the pages :
In case of include() and require() you can re-declared the same page multiple times
where as include_once() and require_once() evaluate the multiple existence of file , if file exist do not allow you the include the same file multiple times .
In the same way include_once() create warning messages where as require_once() gives fatal error and halt the execution of the program .