浮点问题用C [英] Floating point issue in C

问题描述

  

可能重复：结果
  <一href=\"http://stackoverflow.com/questions/1839422/strange-output-in-comparision-of-float-with-float-literal\">strange在浮动的比较输出浮动文字

 浮动= 0.7;
如果（一个或下; 0.7）;
 

为什么这里的前pression评估为真？

解决方案

浮点数限制了precision。 0.7最有可能不能准确地重新presented，所以在该值可能是0.6999999999982左右的浮子。此相比，双0.7（这是更precise：0.6999999999999999999999999384）将表明，它是以下

。

检查了这一点：<一href=\"http://docs.sun.com/source/806-3568/ncg_goldberg.html\">http://docs.sun.com/source/806-3568/ncg_goldberg.html

Possible Duplicate:
strange output in comparision of float with float literal

float a = 0.7;
if (a < 0.7) ;

Why does the expression here evaluate to true?

解决方案

Floating point numbers have limited precision. 0.7 most likely can't be exactly represented, so the value in a might be 0.6999999999982 or so in a float. This compared to a double 0.7 (which is more precise: 0.6999999999999999999999999384) will show that it is less.

Check this out: http://docs.sun.com/source/806-3568/ncg_goldberg.html

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