{"id":1856,"date":"2016-01-02T18:24:07","date_gmt":"2016-01-02T23:24:07","guid":{"rendered":"http:\/\/www.ikriv.com\/blog\/?p=1856"},"modified":"2016-01-02T18:24:07","modified_gmt":"2016-01-02T23:24:07","slug":"php-simplexml-is-broken-part-1","status":"publish","type":"post","link":"https:\/\/ikriv.com\/blog\/?p=1856","title":{"rendered":"PHP SimpleXML is broken: Part 1"},"content":{"rendered":"

The following code does not<\/b> work as expected:<\/p>\n

<\/p>\n

\n$xml = simplexml_load_string(\"<root><a\/><b>text<\/b><\/root>\");\n$node = $xml->xpath(\"\/root\/a\")[0];\nif ($node)<\/b> process($node); \/\/ process($node) may not be called for some valid nodes<\/font><\/pre>\n
<\/code><\/p>\n
Unlike most other objects, SimpleXmlElement<\/code> may evaluate as false<\/b> even when it is not null. Specifically, SimpleXmlElements<\/code> representing empty tags (like “<a \/>) will evaluate as false<\/b>, so process($node)<\/code> won’t be called for them.<\/p>\n
Yes, they made a special case for it in the language definition. E.g. DOMElement<\/code> representing an empty tag won’t evaluate to false, at least not according to the documentation.<\/p>\n
So, in my previous post “Node is null” should read “Node evaluates to false”, but it is still a bug, since it was not an empty tag.<\/p>\n
When you write if (something)<\/code> that something will be converted to Boolean per the below conversion rules. Most of them make sense, but some of them totally don’t. If you want to check for null<\/b>, you’d better do it explicitly: if (something !== null)<\/code>.<\/p>\n
PHP Boolean Conversion Rules<\/h2>\n
Per the PHP documentation on Boolean<\/a> (comments are mine):<\/p>\n
When converting to boolean, the following values are considered FALSE<\/b>:<\/p>\n\n\n\n\n\n\n\n\n\n\n
the boolean FALSE<\/b> itself<\/td>\nTotally makes sense<\/td>\n<\/tr>\n
the integer 0 (zero)<\/td>\nLike in C\/C++, so it is expected, even if may not make perfect sense<\/td>\n<\/tr>\n
the float 0.0 (zero)<\/td>\nLike in C\/C++, so it is expected, even though it makes even less sense<\/td>\n<\/tr>\n
the empty string<\/font><\/td>\nNot like in C\/C++, but sort of makes sense<\/td>\n<\/tr>\n
and the string “0”<\/font><\/td>\nWhy?! Because it represents integer 0? How about string “0.0” then? Or string “false”?<\/td>\n<\/tr>\n
an array with zero elements<\/font><\/td>\nSort of makes sense<\/font><\/td>\n<\/tr>\n
an object with zero member variables (PHP 4 only)<\/td>\nDoes not make sense, but they deprecated it<\/td>\n<\/tr>\n
the special type NULL (including unset variables)<\/td>\nTotally makes sense<\/td>\n<\/tr>\n
SimpleXML objects created from empty tags<\/font><\/td>\nWhy?! Who came up with this wonderful idea?<\/td>\n<\/tr>\n<\/table>\n
Rest in peace, dear rule of least astonishment. You should never have ventured in that cruel PHP land.<\/p>\n","protected":false},"excerpt":{"rendered":"
The following code does not work as expected: $xml = simplexml_load_string(“<root><a\/><b>text<\/b><\/root>”); $node = $xml->xpath(“\/root\/a”)[0]; if ($node) process($node); \/\/ process($node) may not be called for some valid nodes Unlike most other […]<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"Layout":"","footnotes":""},"categories":[4,5,15],"tags":[],"class_list":["entry","author-ikriv","post-1856","post","type-post","status-publish","format-standard","category-hack","category-dev","category-webdev"],"_links":{"self":[{"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1856","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1856"}],"version-history":[{"count":0,"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1856\/revisions"}],"wp:attachment":[{"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1856"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1856"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ikriv.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1856"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}