php变量判断，存在，定义，真，空

小咪咪 2024-04-18 09:33 62阅读 0赞

<table> 
 <thead> 
  <tr> 
   <th>变量x</th> 
   <th>gettype()</th> 
   <th>if()</th> 
   <th>empty()</th> 
   <th>is_null()</th> 
   <th>isset()</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>var $x</td> 
   <td>NULL</td> 
   <td>false</td> 
   <td>true</td> 
   <td>true</td> 
   <td>false</td> 
  </tr> 
  <tr> 
   <td>$x is undefined</td> 
   <td>NULL</td> 
   <td>false</td> 
   <td>true</td> 
   <td>true</td> 
   <td>false</td> 
  </tr> 
  <tr> 
   <td>$x = array()</td> 
   <td>array</td> 
   <td>false</td> 
   <td>true</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = “”</td> 
   <td>string</td> 
   <td>false</td> 
   <td>true</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = null</td> 
   <td>NULL</td> 
   <td>false</td> 
   <td>true</td> 
   <td>true</td> 
   <td>false</td> 
  </tr> 
  <tr> 
   <td>$x = false</td> 
   <td>boolean</td> 
   <td>false</td> 
   <td>true</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = true</td> 
   <td>boolean</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = “false”</td> 
   <td>string</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = “true”</td> 
   <td>string</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = 1</td> 
   <td>integer</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = 99</td> 
   <td>integer</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = 0</td> 
   <td>integer</td> 
   <td>false</td> 
   <td>true</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = -1</td> 
   <td>integer</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = “1”</td> 
   <td>string</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = “0”</td> 
   <td>string</td> 
   <td>false</td> 
   <td>true</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = “1”</td> 
   <td>string</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
  <tr> 
   <td>$x = “hello”</td> 
   <td>string</td> 
   <td>true</td> 
   <td>false</td> 
   <td>false</td> 
   <td>true</td> 
  </tr> 
 </tbody> 
</table>