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FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN

From cppreference.com
< c‎ | numeric‎ | math
 
 
 
Common mathematical functions
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Classification
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Macro constants
FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN
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Defined in header <math.h>
#define FP_NORMAL    /*implementation defined*/
(since C99)
#define FP_SUBNORMAL /*implementation defined*/
(since C99)
#define FP_ZERO      /*implementation defined*/
(since C99)
#define FP_INFINITE  /*implementation defined*/
(since C99)
#define FP_NAN       /*implementation defined*/
(since C99)

The FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN macros each represent a distinct category of floating-point numbers. They all expand to an integer constant expression.

Constant Explanation
FP_NORMAL indicates that the value is normal, i.e. not an infinity, subnormal, not-a-number or zero
FP_SUBNORMAL indicates that the value is subnormal
FP_ZERO indicates that the value is positive or negative zero
FP_INFINITE indicates that the value is not representable by the underlying type (positive or negative infinity)
FP_NAN indicates that the value is not-a-number (NaN)

[edit] Example

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

[edit] See also

classifies the given floating-point value
(function) [edit]
C++ documentation for FP_categories