Home Original page

fpclassify - cppreference.com

From cppreference.com

#define fpclassify(arg) /* implementation defined */

 (since C99)

Categorizes floating-point value arg into the following categories: zero, subnormal, normal, infinite, NAN, or implementation-defined category. The macro returns an integral value.

FLT_EVAL_METHOD is ignored: even if the argument is evaluated with more range and precision than its type, it is first converted to its semantic type, and the classification is based on that: a normal long double value might become subnormal when converted to double and zero when converted to float.

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

#include <float.h>
#include <math.h>
#include <stdio.h>

const char* show_classification(double x)
{
    switch(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(void)
{
    printf("1.0/0.0 is %s\n", show_classification(1 / 0.0));
    printf("0.0/0.0 is %s\n", show_classification(0.0 / 0.0));
    printf("DBL_MIN/2 is %s\n", show_classification(DBL_MIN / 2));
    printf("-0.0 is %s\n", show_classification(-0.0));
    printf("1.0 is %s\n", show_classification(1.0));
}

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

References

  • C23 standard (ISO/IEC 9899:2024):
  • 7.12.3.1 The fpclassify macro (p: TBD)
  • C17 standard (ISO/IEC 9899:2018):
  • 7.12.3.1 The fpclassify macro (p: TBD)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.12.3.1 The fpclassify macro (p: 235)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.12.3.1 The fpclassify macro (p: 216)

See also