empty、isset、is_null的比较

直接上代码

<?php
$a=0;
$b=‘0‘;
$c=0.0;
$d=‘‘;
$e=NULL;
$f=array();
$g=‘\0‘;
$h=‘ ‘;//space
$i=true;
$j=false;
$k;// a variable declared, but without a value

$_arr=get_defined_vars();
array_splice($_arr,0,7);  

foreach($_arr as $k=>$v){
    var_dump(!is_null($v));
    var_dump(!empty($v));
    var_dump(isset($v));
    echo ‘<br/>‘;
}

//END

结果

boolean true
boolean false
boolean true

boolean true
boolean false
boolean true

boolean true
boolean false
boolean true

boolean true
boolean false
boolean true

boolean false
boolean false
boolean false

boolean true
boolean false
boolean true

boolean true
boolean true
boolean true

boolean true
boolean true
boolean true

boolean true
boolean true
boolean true

boolean true
boolean false
boolean true

总结：

1、is_null 和 isset基本一样

2、empty() is the opposite of (boolean) var, except that no warning is generated when the variable is not set.(手册上说的)

3、$k没有获取到，那肯定is_null了