简单教程
提交运行
代码编辑器：
<?php echo substr("Hello world",10),"<br>"; echo substr("Hello world",1), "<br>"; echo substr("Hello world",3), "<br>"; echo substr("Hello world",7), "<br>"; echo substr("Hello world",-1), "<br>"; echo substr("Hello world",-10), "<br>"; echo substr("Hello world",-8),"<br>"; echo substr("Hello world",-4),"<br>";
运行结果：