发现一个四舍五入奇怪的问题，有没有人可以解释下

[ashengy]

代码：
//四舍五入取两位小数
$poundage = 0.105;
echo $poundage . "<BR>";
echo sprintf ( "%.2f", $poundage ) . "<BR>";
echo "<BR>-----------------------------<BR>";
$poundage = 0.205;
echo $poundage . "<BR>";
echo sprintf ( "%.2f", $poundage ) . "<BR>";
echo "<BR>-----------------------------<BR>";
$poundage = 0.305;
echo $poundage . "<BR>";
echo sprintf ( "%.2f", $poundage ) . "<BR>";
echo "<BR>-----------------------------<BR>";
$poundage = 0.405;
echo $poundage . "<BR>";
echo sprintf ( "%.2f", $poundage ) . "<BR>";
echo "<BR>-----------------------------<BR>";

//显示结果
-----------------------------
0.105
0.10

-----------------------------
0.205
0.20

-----------------------------
0.305
0.30

-----------------------------
0.405
0.41

-----------------------------

按理说第三位为5，四舍五入，都应进1。可却出现了这种情况。有人知道为什么吗

[lijpwsw]

浮点数有时候会丢失精度的

[lijpwsw]

http://www.laruence.com/2013/03/26/2884.html

[小菜鸟czh]

round 函数四舍五入不就行了

[wirror800]

#4楼正解

引用 4 楼 lijpwsw 的回复:

http://www.laruence.com/2013/03/26/2884.html

[tottyandbaty]

sprintf 不具有四舍五入的功能

[xuzuning]

建议你认真复习一下 计算机基础：浮点数的表示 printf('%.18f', 0.305); //0.304999999999999993