如何设置log10(0)的返回值? [英] How to set returned value of log10(0)?

问题描述

它会向我显示 -inf .我要使用的每个库/编译器是否都已修复?

It prints to me -inf. Is it fixed for every library/compiler I'll use?

代码:

#include <iostream>
#include <math.h>

using namespace std;

int main ()
{
  double result = log10(0.0);
  cout << result;
}

还是可以在不同的平台上进行更改?您如何管理 pole错误并保持 double ?

Or could it change in different platforms? How would you manage the pole error keeping double?

推荐答案

根据 cplusplus ，这取决于您从库中获得的 log10(0).但是，通常未定义 log10(0)的值(如果愿意，可以是 -inf ，但它不是实数).通常，您应该在发生这种不确定的结果之前 防止发生这种不确定的结果(从C ++的未定义的行为"的角度来看不是未定义的，而是从数学的意义上来说是未定义的).例如.

According to cplusplus, it depends on the library what you get for log10(0). However, in general the value of log10(0) is not defined (can be -inf if you like, but it is not a real number). Usually, you should prevent such undefined results (not undefined in the C++ sense of Undefined Behaviour, but in a mathematical sense) before they happen. E.g.

double x;
x = foo();
if ( x <= 0 ) {
    /* handle this case extra */
else {
    y = log10(x);
}

在 log10(0)情况下使用什么值在很大程度上取决于您的应用程序.但是，我认为在进行计算之前检查 0 更容易，而不是依赖 log10(0)返回某些特定值(因为它可能是-inf 或完全不同的东西).

What value you use in the case of log10(0) depends very much on your application. However, I think it is easier to check for 0 before doing the calculation instead of relying on log10(0) returning some particular value (as it might be -inf or something completely different).

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