# std::fpclassify

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
int fpclassify( float arg ); | (1) | (since C++11)
int fpclassify( double arg ); | (2) | (since C++11)
int fpclassify( long double arg ); | (3) | (since C++11)
int fpclassify( Integral arg ); | (4) | (since C++11)

1-3) Categorizes floating point value `arg` into the following categories: zero, subnormal, normal, infinite, NAN, or implementation-defined category.
4) A set of overloads or a function template accepting the `from` argument of any integral type. Equivalent to (2) (the argument is cast to double).

### Parameters

arg | - | floating point value

### Return value

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

### Example

Run this code

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

    const char* 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)
C documentation for fpclassify

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