php-basic "Variable detection"

Detection of variables

Isset ($var/// using isset to check if a variable exists, this PHP comes with a method that is often used later

// Test---Example 1: if (Isset ($a)) {    " variable a exists ";}Else{     " variable A does not exist " ;}

Results of the output

Variable A does not exist   // because A is not defined

Example 2 below:

$b =null// defined as nullif(Isset ($b)) {    " variable B exists "  ;}Else{    " variable B does not exist ";}

Results:

Variable B does not exist   // variable B is determined to                 not exist // Although it is determined if there is a variable in memory, it is                not related to the value of the variable.  However, if you use Isset to test a variable that is set to NULL, FALSE is returned.                 // Then there is the example 2 output variable B does not exist result.  

Example 3:

$c ='// defined as nullif(Isset ($c)) {    " variable C exists  ";}Else{    " variable C does not exist ";}  // Output results
C is an empty string variable, its value is not empty?, in fact, it is empty, but its value is empty, like a person, there is a bank card, but there is no money in the card,
C is an empty string or a 0  variable is present, and it is loaded with something--and value. It's just too few things to pack.
Variable C exists

PS: Use isset to check the variable, if the variable is null will be returned false

php-Base "Variable detection"