Determine if a floating point number is Nan (INF) in vc6)

Nan indicates not a number.

After Division by zero, the floating point will become Nan (INF ).

You can use the following functions to determine whether the value is Nan (INF ).

Library Function: int _ isnan (double );

Int _ finite (double); // use this function in VC

// If the input double value is invalid, the function returns 0. You need to include the library file <float. h>

You can also write user-defined functions for judgment (not in VC)

1 bool is_nan(double dVal)
2 {
3 　　if (dVal==dVal)
4 　　　　return false;
5 
6 　　return true;
7 }

The invalid value in vc6 is1. # inf000000000

 This value varies with compilers.

This difference can be shielded using the C ++ standard library. The following code:

#include <limits>

bool is_nan(double dVal)
{
　　double dNan = std::numeric_limits<double>::quiet_NaN();
　　if (dVal==dNan)
　　　　return true;

　　return false;
}

The following functions can be used in boost to determine

#include <boost/math/special_functions/fpclassify.hpp>

template <class T> bool isfinite(T z);
template <class T> bool isinf(T t);
template <class T> bool isnan(T t);
template <class T> bool isnormal(T t);