<?php
echo substr_replace("1234567890","",2)
输出string(6) "12"
?>
为空则是删除
echo substr_replace("1234567890","5",2);
输出string(4) "125"
<?php
echo substr_replace("1234567890","5",-2)
输出string(6) "123456785"
?>
<?php
echo substr_replace("1234567890","5",0);
输出string(1) "5"
?>
<?php
echo substr_replace("1234567890","5",0,0);
输出string(11) "51234567890"
?>