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C++

Reference

C library:
- <cassert> (assert.h)
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- <cerrno> (errno.h)
- C++11
  <cfenv> (fenv.h)
- <cfloat> (float.h)
- C++11
  <cinttypes> (inttypes.h)
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
- C++11
  <cstdbool> (stdbool.h)
- <cstddef> (stddef.h)
- C++11
  <cstdint> (stdint.h)
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
- C++11
  <ctgmath> (tgmath.h)
- <ctime> (time.h)
- C++11
  <cuchar> (uchar.h)
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
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Input/Output:
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Multi-threading:
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Other:
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<cmath> (math.h)

functions
- abs
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  fpclassify
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  hypot
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  ilogb
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  isfinite
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  isgreater
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  isgreaterequal
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  islessgreater
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  scalbn
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macro constants
- HUGE_VAL
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  HUGE_VALF
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  HUGE_VALL
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  INFINITY
- C++11
  math_errhandling
- NAN
types
- C++11
  double_t
- float_t

Reference
<cmath>
fpclassify

macro/function

fpclassify

macro	fpclassify(x)

function	int fpclassify (float x);int fpclassify (double x);int fpclassify (long double x);

Classify floating-point value

Returns a value of type int that matches one of the classification macro constants, depending on the value of x:

value	description
`FP_INFINITE`	Positive or negative infinity (overflow)
`FP_NAN`	Not-A-Number
`FP_ZERO`	Value of zero
`FP_SUBNORMAL`	Sub-normal value (underflow)
`FP_NORMAL`	Normal value (none of the above)

Note that each value pertains to a single category: zero is not a normal value.

These macro constants of type int are defined in header <cmath> (<math.h>).

In C, this is implemented as a macro, but the type of x shall be float, double or long double.

In C++, it is implemented with function overloads for each floating-point type.

Parameters

x

Return value

One of the followoing int values: FP_INFINITE, FP_NAN, FP_ZERO, FP_SUBNORMAL or FP_NORMAL.

Example

/* fpclassify example */
#include <stdio.h>      /* printf */
#include <math.h>       /* fpclassify, signbit, FP_* */

int main()
{
  double d = 1.0 / 0.0;
  switch (fpclassify(d)) {
    case FP_INFINITE:  printf ("infinite");  break;
    case FP_NAN:       printf ("NaN");       break;
    case FP_ZERO:      printf ("zero");      break;
    case FP_SUBNORMAL: printf ("subnormal"); break;
    case FP_NORMAL:    printf ("normal");    break;
  }
  if (signbit(d)) printf (" negative\n");
  else printf (" positive or unsigned\n");
  return 0;
}

Output:


infinite positive or unsigned

functions

macro constants

types

fpclassify

Parameters

Return value

Example

See also