PHP provides four functions which enable you to insert code from other files.<\/p>\n\n\n\n
* include()
* require()
* include_once()
* require_once()<\/p>\n\n\n\n
All four can take a local file or URL as input. None of them can import a remote file. require() and include() functions are virtually similar in their function except for the way they handle an irretrievable resource. include() and include_once() provide a warning if the resource cannot be retrieved and try to continue execution of the program if possible. require() and require_once functions provide stop processing the page if they cannot retrieve the resource.<\/p>\n\n\n\n
Why include_once() and require_once()<\/strong> File A.php includes File B.php and C.php File C.php has been included twice, so the interpreter would print an error. Since a function cannot be redefined once it\u2019s declared, this restriction can help prevent errors.<\/p>\n\n\n\n If both File A.php and File B.php use include_once() or require_once() to import File C.php, no errors would be generated. PHP would understand that you only want one instance of the code in File C and would not try to redeclare the functions.<\/p>\n\n\n\n It is best to use require_once() to include files which contain necessary code and include_once() to include files that contain content which the program can run without e.g. HTML, CSS, etc.<\/p>\n","protected":false},"excerpt":{"rendered":" PHP provides four functions which enable you to insert code from other files. * include()* require()* include_once()* require_once() All four can take a local file or URL as input. None of them can import a remote file. require() and include() functions are virtually similar in their function except for the way they handle an irretrievable […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[24],"class_list":["post-340","post","type-post","status-publish","format-standard","hentry","category-php","tag-php"],"_links":{"self":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts\/340","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/comments?post=340"}],"version-history":[{"count":1,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts\/340\/revisions"}],"predecessor-version":[{"id":341,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts\/340\/revisions\/341"}],"wp:attachment":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/media?parent=340"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/categories?post=340"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/tags?post=340"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
The include_once() and require_once() functions are handy in situations where multiple files may reference the same included code. For example:<\/p>\n\n\n\n
File B.php includes File C.php<\/p>\n\n\n\n