php5.4 round,php的round四含五入问题

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php的round四含五入问题

作者：大鹏发布于：2007-6-6 16:34 Wednesday

分类：PHP&MySql

代码:

[codes=php]<?php

echo "round(5.005,2)=".round(5.005,2)."\n";

echo "round(5.015,2)=".round(5.015,2)."\n";

echo "round(5.025,2)=".round(5.025,2)."\n";

echo "round(5.035,2)=".round(5.035,2)."\n";

echo "round(5.045,2)=".round(5.045,2)."\n";

echo "round(5.055,2)=".round(5.055,2)."\n";

echo "round(5.065,2)=".round(5.065,2)."\n";

echo "round(5.075,2)=".round(5.075,2)."\n";

echo "round(5.085,2)=".round(5.085,2)."\n";

echo "round(5.095,2)=".round(5.095,2)."\n";

$m=0.000000000000001;

echo "\n";

echo "round(5.005+{$m},2)=".round(5.005+$m,2)."\n";

echo "round(5.015+{$m},2)=".round(5.015+$m,2)."\n";

echo "round(5.025+{$m},2)=".round(5.025+$m,2)."\n";

echo "round(5.035+{$m},2)=".round(5.035+$m,2)."\n";

echo "round(5.045+{$m},2)=".round(5.045+$m,2)."\n";

echo "round(5.055+{$m},2)=".round(5.055+$m,2)."\n";

echo "round(5.065+{$m},2)=".round(5.065+$m,2)."\n";

echo "round(5.075+{$m},2)=".round(5.075+$m,2)."\n";

echo "round(5.085+{$m},2)=".round(5.085+$m,2)."\n";

echo "round(5.095+{$m},2)=".round(5.095+$m,2)."\n";

?> [/codes]

结果:

round(5.005,2)=5.01

round(5.015,2)=5.01

round(5.025,2)=5.03

round(5.035,2)=5.04

round(5.045,2)=5.05

round(5.055,2)=5.06

round(5.065,2)=5.07

round(5.075,2)=5.08

round(5.085,2)=5.09

round(5.095,2)=5.1

round(5.005+1E-015,2)=5.01

round(5.015+1E-015,2)=5.02

round(5.025+1E-015,2)=5.03

round(5.035+1E-015,2)=5.04

round(5.045+1E-015,2)=5.05

round(5.055+1E-015,2)=5.06

round(5.065+1E-015,2)=5.07

round(5.075+1E-015,2)=5.08

round(5.085+1E-015,2)=5.09

round(5.095+1E-015,2)=5.1

PHP手册:

例子 1. round() 例子

[codes=php]<?php

echo round(3.4); // 3

echo round(3.5); // 4

echo round(3.6); // 4

echo round(3.6, 0); // 4

echo round(1.95583, 2); // 1.96

echo round(1241757, -3); // 1242000

echo round(5.045, 2); // 5.04

echo round(5.055, 2); // 5.06

?> [/codes]

注意

在对正好一半的分数进行舍入时 round() 在偶数次舍去，在奇数次进位。如果你想迫使它对 .5(或 .05)总向一个方向舍入，加上或减去一个很小的因子。对一半值舍去对另一半值进一的背后原因是避免传统的银行问题，即如果总是舍去则银行从顾客那里多拿了钱，如果总是进一则银行最终会损失了钱。对此平均舍入则在统计上达到了平衡。

PHP手册中

echo round(5.045, 2); // 5.04

echo round(5.055, 2); // 5.06

而我代码的结果却是:

round(5.045,2)=5.05

round(5.055,2)=5.06

round(5.005,2)=5.01

round(5.015,2)=5.01

round(5.025,2)=5.03

round(5.035,2)=5.04

round(5.045,2)=5.05

round(5.055,2)=5.06