# std::fpclassify

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
| (1) |
int fpclassify( float num ); int fpclassify( double num ); int fpclassify( long double num ); |  | (since C++11) (until C++23)
constexpr int fpclassify( /* floating-point-type */ num ); |  | (since C++23)
Additional overloads |  |
Defined in header `<cmath>` |  |
template< class Integer > int fpclassify( Integer num ); | (A) | (since C++11) (constexpr since C++23)

1) Categorizes floating point value num into the following categories: zero, subnormal, normal, infinite, NAN, or implementation-defined category. The library provides overloads of `std::fpclassify` for all cv-unqualified floating-point types as the type of the parameter num. (since C++23)
A) Additional overloads are provided for all integer types, which are treated as double.

### Parameters

num | - | floating-point or integer value

### Return value

one of FP_INFINITE, FP_NAN, FP_NORMAL, FP_SUBNORMAL, FP_ZERO or implementation-defined type, specifying the category of num.

### Notes

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::fpclassify(num) has the same effect as std::fpclassify(static_cast<double>(num)).

### Example

Run this code

    #include <cfloat>
    #include <cmath>
    #include <iostream>

    auto show_classification(double x)
    {
        switch (std::fpclassify(x))
        {
            case FP_INFINITE:
                return "Inf";
            case FP_NAN:
                return "NaN";
            case FP_NORMAL:
                return "normal";
            case FP_SUBNORMAL:
                return "subnormal";
            case FP_ZERO:
                return "zero";
            default:
                return "unknown";
        }
    }

    int main()
    {
        std::cout << "1.0/0.0 is " << show_classification(1 / 0.0) << '\n'
                  << "0.0/0.0 is " << show_classification(0.0 / 0.0) << '\n'
                  << "DBL_MIN/2 is " << show_classification(DBL_MIN / 2) << '\n'
                  << "-0.0 is " << show_classification(-0.0) << '\n'
                  << "1.0 is " << show_classification(1.0) << '\n';
    }

Output:

    1.0/0.0 is Inf
    0.0/0.0 is NaN
    DBL_MIN/2 is subnormal
    -0.0 is zero
    1.0 is normal

### See also

isfinite (C++11) | checks if the given number has finite value (function)
isinf (C++11) | checks if the given number is infinite (function)
isnan (C++11) | checks if the given number is NaN (function)
isnormal (C++11) | checks if the given number is normal (function)
numeric_limits | provides an interface to query properties of all fundamental numeric types. (class template)

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