Var_dump ( $abc ) // object(stdClass)#1 (1) Var_dump (isset( $def -> ghi -> jkl )) // bool(false) Var_dump (isset( $def -> ghi )) // bool(false) Var_dump (isset( $abc -> def -> ghi -> jkl )) // bool(false) Var_dump (isset( $abc -> def -> ghi )) // bool(false) Var_dump (isset( $abc -> def )) // bool(true) Without raising any errors, warnings or notices. Isset($abc) & isset($abc->def) & isset($abc->def->ghi) You can safely use isset to check properties and subproperties of objects directly. However you can use it for checking if array keys exists inside a function It won't work for variables declared locally inside a function Var_dump ( is_set ( 'age', array())) // false Var_dump ( is_set ( 'age', $arr1 )) // false Var_dump ( is_set ( 'age', null )) // true If (! array_key_exists ( $name, $array ? $GLOBALS )) return false its similar to array_key_exists but, its a lot more flexible and can check for multiple array keys across multiple arrays. If you are annoyed by the behavior of isset() concerning null values, here is a handy function for you. Getting Started Introduction A simple tutorial Language Reference Basic syntax Types Variables Constants Expressions Operators Control Structures Functions Classes and Objects Namespaces Enumerations Errors Exceptions Fibers Generators Attributes References Explained Predefined Variables Predefined Exceptions Predefined Interfaces and Classes Predefined Attributes Context options and parameters Supported Protocols and Wrappers Security Introduction General considerations Installed as CGI binary Installed as an Apache module Session Security Filesystem Security Database Security Error Reporting User Submitted Data Hiding PHP Keeping Current Features HTTP authentication with PHP Cookies Sessions Dealing with XForms Handling file uploads Using remote files Connection handling Persistent Database Connections Command line usage Garbage Collection DTrace Dynamic Tracing Function Reference Affecting PHP's Behaviour Audio Formats Manipulation Authentication Services Command Line Specific Extensions Compression and Archive Extensions Cryptography Extensions Database Extensions Date and Time Related Extensions File System Related Extensions Human Language and Character Encoding Support Image Processing and Generation Mail Related Extensions Mathematical Extensions Non-Text MIME Output Process Control Extensions Other Basic Extensions Other Services Search Engine Extensions Server Specific Extensions Session Extensions Text Processing Variable and Type Related Extensions Web Services Windows Only Extensions XML Manipulation GUI Extensions Keyboard Shortcuts ? This help j Next menu item k Previous menu item g p Previous man page g n Next man page G Scroll to bottom g g Scroll to top g h Goto homepage g s Goto search
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