如何使用FMOD，避免precision问题

本文介绍了如何使用FMOD，避免precision问题的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我要归结这个问题最简单的形式：

for(double d=0.0; d<=5.0; d+=0.05) {
  if(fmod(d,0.25) is equal 0)
    print 'X';
}

This will of course not work since d will be [0, 0.05000000001, 0.100000000002, ...] causing fmod() to fail. Extreme example is when d=1.999999999998 and fmod(d,0.25) = 1.

How to tackle this? Here is an editable online example.

解决方案

I'd solve this by simply not using floating point variables in that way:

for (int i = 0; i <= 500; i += 5) {
  double d = i / 100.0;  // in case you need to use it.
  if ((i % 25) == 0)
    print 'X';
}

They're usually problematic enough that it's worth a little extra effort in avoiding them.

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