float转换为整形的怪异问题-PHP Tutorial-php.cn

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float转换为整形的怪异问题

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Jun 23, 2016 pm 02:14 PM

for($i=0;$i $sum+=0.1;
}
echo (int)$sum;

为什么输出的是0而不是1

回复讨论(解决方案)

引用手册

Warning关于浮点数精度的警告 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 7.9999999999999...。 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 0.3333333333333...。 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。

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