Linux 如何检查双变量中的 inf（和 | 或）NaN
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How to check for inf (and | or) NaN in a double variable
提问by nakiya
Consider the following code:
考虑以下代码：
#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
template<class T>
bool IsNaN(T t)
{
return t != t;
}
int main(int argc, char**argv)
{
double d1, d2;
sscanf(argv[1], "%f", &d1);
sscanf(argv[2], "%f", &d2);
double dRes = d1/d2;
cout << "dRes = " << dRes << "\n";
if(IsNaN(dRes))
cout << "Is NaN\n";
else
cout << "Not NaN\n";
}
Couple of questions:
几个问题：
- When I pass 0 and 0 as arguments, it outputs
dRes = inf. But I was expectingdRes = NaNor something like that. - Is NaN representable in double variables? For that matter, any variable?
- When I changed the data type of d1,d2,dRes to int and passed 0 and 0, I got a
Floating exception. What is the difference? - How to check if a variable's value is equal to
inf?
- 当我将 0 和 0 作为参数传递时，它输出
dRes = inf. 但我在期待dRes = NaN或类似的东西。 - NaN 可以用双变量表示吗？就此而言，任何变量？
- 当我将 d1,d2,dRes 的数据类型更改为 int 并传递 0 和 0 时，我得到了一个
Floating exception. 有什么不同？ - 如何检查变量的值是否等于
inf？
采纳答案by kennytm
When using
scanf()doubleshould be read using%lf, not%f.%fwill convert the input into a 32-bitfloat, so the first 32 bits of your variables will be filled with some invalid data, and the last 32 bits will be left as garbage.Yes.
#include <limits>, thenstd::numeric_limits<double>::quiet_NaN(). Some compilers (e.g. gcc) also provides theNANmacro in<cmath>.There is no NaN or infinity for integer types. Divide-by-zero for integer will cause an exception (SIGFPE).
#include <cmath>, thenstd::isinf(x). Usestd::isfinite(x)to ensurexis not NaN or Infinity.
使用时
scanf()double应该读使用%lf，而不是%f。%f将输入转换为 32 位float，因此变量的前 32 位将填充一些无效数据，最后 32 位将作为垃圾留下。是的。
#include <limits>，那么std::numeric_limits<double>::quiet_NaN()。一些编译器（例如GCC）也提供了NAN宏<cmath>。整数类型没有 NaN 或无穷大。整数除以零将导致异常 (SIGFPE)。
#include <cmath>，那么std::isinf(x)。使用std::isfinite(x)，以确保x不NAN或无穷大。
回答by user9137229
Just do it like that:
就这样做：
if (dRes == +1.0/0.0 || dRes == -1.0/0.0) ... //+INF, -INF
if (dRes == +0.0/0.0 ) ... //+NaN; i.e. pow(2.0 ,16384.0)
回答by Ben Voigt
The function fpclassifywill let you inspect a floating-point value for all the special cases.
该函数fpclassify将让您检查所有特殊情况的浮点值。
It's found in <math.h>as a macro since C99, and in <cmath>as a family of functions, for float, double, and long doubleunder the overloaded name std::fpclassifysince C++11.
它的发现<math.h>为自C99宏，并<cmath>作为家庭的功能，float，double，和long double重载的名义下std::fpclassify，因为C ++ 11。
cppreference has a nice example
cppreference 有一个很好的例子
