The differences between is_null empty isset and unset in php are described in detail
- 2020-06-01 08:37:31
is_null, empty, isset, unset let's look at the descriptions of these four functions first.
isset to determine if the variable already exists (configuration)
unset deletes (releases) the variable
empty determines whether the variable is empty
is_null determines whether the variable is NULL
ok, it's already started. So at the beginning, of these four functions, except unset, the other three are judgment functions, unset is out first, because he can't make a mistake, is_null, we can view it as! isset is an inverse operation of isset. The following table can clearly illustrate the relationship between them:
variable empty is_null isset $a= "" true false true $a=null true true false var $a true true false $a=array() true false true $a=false true false true $a=15 false false true $a=1 false false true $a=0 true false true $a= " 0 " true false true $a= " true " false false true $a= " false " false false true
From this, we can find that as long as the variable is "or" or 0, or false and null, empty will return true, and isset is to judge whether the variable exists or not. As long as the variable is not null or not assigned, the return result is true, and is_null is exactly the opposite result of isset.
Of course, if you just want to do the following work:
echo! isset ($_GET [' a ']); // if the value of the variable a is not available
echo empty ($_GET [' a ']); // if the value of the variable a is empty
So it turns out to be all 1, and you can use both.