判断php变量是不是定义，是否为空

判断php变量是否定义，是否为空isset() 【1】PHP 8.5.5PHP 8.5.5 是 PHP 8.5 分支的维护更新版本。该版本延续了“小步快跑”的迭代逻辑，通过深度错误修复、底层性能微调以及安全加固，旨在为开发者提供一个更健壮、更高效的运行环境。该版本严格遵守语义化版本规范，不包含破坏性变更。下载Returns?TRUE?if?var?exists and has value other than?NULL,?FALSE?otherwise.输入可以是多个变量，只有所有的变量为真的时候，返回真empty()【2】Returns?FALSE?if?var?has a non-empty and non-zero value.The following things are considered to be empty:"" (an empty string)0 (0 as an integer)"0" (0 as a string)NULLFALSEarray() (an empty array)var $var; (a variable declared, but without a value in a class)输入只能是一个变量is_null() 【3】Returns?TRUE?if?var?is?null?,?FALSE?otherwise.???? A variable is considered to be?null?if:it has been assigned the constant?NULL.it has not been set to any value yet.it has been?unset(). ? ???使用 PHP 函数对变量?$x?进行比较表达式gettype()empty()is_null()isset()if($x) Boolean$x = "";stringTRUEFALSETRUEFALSE$x = null;NULLTRUETRUEFALSEFALSEvar $x;NULLTRUETRUEFALSEFALSE$x?is undefinedNULLTRUETRUEFALSEFALSE$x = array();arrayTRUEFALSETRUEFALSE$x = false;booleanTRUEFALSETRUEFALSE$x = true;booleanFALSEFALSETRUETRUE$x = 1;integerFALSEFALSETRUETRUE$x = 42;integerFALSEFALSETRUETRUE$x = 0;integerTRUEFALSETRUEFALSE$x = -1;integerFALSEFALSETRUETRUE$x = "1";stringFALSEFALSETRUETRUE$x = "0";stringTRUEFALSETRUEFALSE$x = "-1";stringFALSEFALSETRUETRUE$x = "php";stringFALSEFALSETRUETRUE$x = "true";stringFALSEFALSETRUETRUE$x = "false";stringFALSEFALSETRUETRUE?（上表没有找到原始来源，谁知道请告诉我）如果变量是一个object该如何呢？?表达式gettype()empty()is_null()isset()if($x) Boolean$x = new object()?objectFALSEFALSETRUETRUE?参考：【1】http://php.net/manual/en/function.isset.php【2】http://www.php.net/manual/en/function.empty.php【3】http://www.php.net/manual/en/function.is-null.php??http://blog.csdn.net/autofei/archive/2010/05/24/5619004.aspx