The difference between empty, is_null and isset

empty(), is_null(), isset() truth table (difference)

1. When the variable is undefined, is_null() and "the parameter itself" are not allowed to be used as parameters for judgment, and a Notice warning error will be reported;
2. Empty and isset will first check whether the variable exists, and then detect the variable value. And is_null and "the parameter itself" just check the variable value directly to see if it is null, so if the variable is not defined, an error will occur!

3. isset(): only if null and undefined, return false;
4. empty(): "", 0, "0", NULL, FALSE, array(), undefined, all return false;
5. is_null(): only determines whether it is null, and reports a warning if it is not defined;
6. The variable itself is used as a parameter, consistent with empty(), but when accepting undefined variables, a warning is reported;
"", 0, "0" , NULL, FALSE, and array(), empty() has the same result as "the variable itself is used as a parameter" and is treated as "empty", while isset() and is_null () are treated as null only. "Empty" is processed (it is worth noting that false is not considered empty)
empty()
If the variable is a non-empty or non-zero value, empty() returns FALSE. In other words, "", 0, "0", NULL, FALSE, array(), var $var, undefined, and objects without any properties will be considered empty, and TRUE will be returned if var is empty. .
isset()
If the variable exists and the value is not NULL, it returns TRUE, otherwise it returns FALSE (including undefined). The variable value is set to: null, and the return value is also false; after unsetting a variable, the variable is canceled. Note that isset handles NULL value variables specially.
  is_null()
  Detect whether the incoming value [value, variable, expression] is null. Only one variable is defined and its value is null, it returns TRUE. Others return FALSE [After undefined variables are passed in Something can go wrong! 】.

The above has introduced the differences between empty, is_null and isset, including the relevant aspects. I hope it will be helpful to friends who are interested in PHP tutorials.