两个FLOAT相加出现的奇怪现象~解决思路
两个FLOAT相加出现的奇怪现象~~~~
- PHP code
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->list ( $usec, $sec ) = explode ( ' ', microtime () );printf("秒：%.16f", (float)$sec);printf("微秒：%.16f", (float)$usec);printf("相加：%.16f", ( float ) $usec + ( float ) $sec);输出结果是：
秒：1327048300.0000000000000000
微秒：0.9687510000000000
相加：1327048300.9687509536743164
我知道浮点数是一个近似值，但是我现在打印$usec且保留小数点后16位的时候，它就是没有小数啊？那不就可以认为它就等于1327048300吗？
它两个相加为什么不是1327048300.9687510000000000呢？？
谢谢！！
------解决方案--------------------
Warning
浮点数精度
显然简单的十进制分数如同 0.1 或 0.7 不能在不丢失一点点精度的情况下转换为内部二进制的格式。这就会造成混乱的结果：例如，floor((0.1+0.7)*10) 通常会返回 7 而不是预期中的 8，因为该结果内部的表示其实是类似 7.9999999999...。
这和一个事实有关，那就是不可能精确的用有限位数表达某些十进制分数。例如，十进制的 1/3 变成了 0.3333333. . .。
所以永远不要相信浮点数结果精确到了最后一位，也永远不要比较两个浮点数是否相等。如果确实需要更高的精度，应该使用任意精度数学函数或者 gmp 函数
------解决方案--------------------
连什么是有效数都弄不清楚，真不明白你们爹妈花许多钱供你们上大学是为什么
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