PHP null value judgment

Although empty and isset are both variable processing functions, they are both used to determine whether the variable has been configured, but they have certain differences: empty will also detect whether the variable is empty or zero. When a variable value is 0, empty considers the variable to be equal to empty, which is equivalent to not being set.

/*For example, to detect the $id variable, when $id=0, use empty and isset to detect whether the variable $id has been configured. Both will return different values ​​- empty is considered not configured. , isset can get the value of ＄id: */
 ＄id=0;
 empty(＄id)?print "It's empty .":print "It's ＄id .";
 //Result: It's empty .
 print " ";
 !isset(＄id)?print "It's empty .":print "It's ＄id .";
 //Result: It's 0 .
?>