PHP: empty, isset, is_null, array (0), array (), array (""), 0, "0", "", "null", NULL summary

PHP: empty, isset, is_null, array (0), array (), array (), 0, 0, null, NULL summary through the following program to detect

$a=0;if(empty($a)){echo "yes|";}else{echo "no|";}if(isset($a)){echo "yes|";}else{echo "no|";}if(is_null($a)){echo "yes|";}else{echo "no|";}if($a){echo "yes|";}else {echo "no|";}

The result of getting different values for $ a is as follows:

Summary:

Empty

1. the variable value is null $ var = "";

2. the variable value is string 0, number 0 $ var = 0, or $ var = "0 ″

3. the variable value is flase $ var = flase;

4. all NULL values are NULL.

5 empty array $ arr = array ();

6. only variables with no value assigned $ var are defined;

Isset

Check whether a variable has been set and is not NULL (Determine if a variable is set and is not NULL)

Is_null

Judge null

Judge whether it is false

1. the variable value is null $ var = "";

2. the variable value is string 0, number 0 $ var = 0, or $ var = "0 ″

3. the variable value is flase $ var = flase;

4. all NULL values are NULL.

5 empty array $ arr = array ();

6. only variables with no value assigned $ var are defined;

Full false

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