Php empty () and isset ()

When using php to write page programs, I often use the variable processing function to determine whether the variable value of a parameter at the end of the php page is null. At the beginning, I used to use the empty () function, but some problems are found. Therefore, the isset () function is used instead.

As the name suggests, empty () determines whether a variable is "null", and isset () determines whether a variable has been set. This so-called "name implies" makes me take some detours at the beginning: When a variable value is equal to 0, empty () will also be True ), as a result, some accidents may occur. Originally, although empty () and isset () are both variable processing functions, they are used to determine whether the variables have been configured, but they have someDifferences:Empty also checks whether the variable is null and zero. When the value of a variable is 0, empty () considers this variable to be null, that is, it is equivalent to not being set.

For example, if the $ id variable is detected and $ id = 0, empty () and isset () are used to check whether the variable $ id has been configured, the two will return different values -- empty () think that there is no configuration, isset () can get the value of $ id:

Copy codeThe Code is as follows: $ id = 0;
Empty ($ id )? Print "It's empty.": print "It's $ id .";
// Result: It's empty.
Print "<br> ";
! Isset ($ id )? Print "It's empty.": print "It's $ id .";
// Result: It's 0.

This means that when we use a variable to process a function, when the variable may have a value of 0, we should be careful when using empty (). In this case, it is more wise to replace it with isset.
When the URL tail parameter of a php page shows id = 0 (for example, test. php? Id = 0), try to compare:Copy codeThe Code is as follows: if (empty ($ id) $ id = 1;-if id = 0, id will also be 1
If (! Isset ($ id) $ id = 1;-if id = 0, id is not 1

Run the following code separately to detect the above inference:Copy codeThe Code is as follows: if (empty ($ id) $ id = 1;
Print $ id; // get 1
If (! Isset ($ id) $ id = 1;
Print $ id; // get 0