/C

# fpclassify

Defined in header `<math.h>`
`#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 <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```
• 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

 isfinite (C99) checks if the given number has finite value (function) isinf (C99) checks if the given number is infinite (function) isnan (C99) checks if the given number is NaN (function) isnormal (C99) checks if the given number is normal (function)

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