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C Library Functions  - nan (3)

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NAME

nan(3f) - [M_units] return a NaN (Not a number) (LICENSE:PD)

CONTENTS

Synopsis
Description
Options
Returns
Example
See Also
Author
License

SYNOPSIS

function nan(value)

     use,intrinsic :: iso_fortran_env, only: real32, real64, real128
     real(kind=real32|real64|real128) :: nan
     real(kind=real32|real64|real128) :: value

DESCRIPTION

Return a NaN (Not a number) value. The type returned will be the same kind as the passed value.

At some point, the IEEE interface should work, with something like

    use,intrinsic :: ieee_arithmetic, only : ieee_value, ieee_quiet_nan
    use,intrinsic :: ieee_arithmetic, only : ieee_support_nan

    if(IEEE_SUPPORT_NAN(x))then        ! Are IEEE NaNs supported?
       x=IEEE_VALUE(x,ieee_quiet_nan)  ! Generate an IEEE value.
    endif

OPTIONS

value	A real value whose kind is used to define the kind of the returned value.

RETURNS

nan	returns a Nan value ("Not a number") on platforms that support NaN values. The kind is determined by the kind of the input value.

EXAMPLE

Sample program

   program demo_nan
   use,intrinsic :: iso_fortran_env, only: real32, real64, real128
   use M_units, only : nan
   implicit none
   real(kind=real32)  :: r32
   real(kind=real64)  :: r64
   real(kind=real128) :: r128
   character(len=256) :: message
   integer            :: ios

      r32=nan(0.0_real32)
      r64=nan(0.0_real64)
      r128=nan(0.0_real128)

      ! examples printing the NaN values
      ! list directed format
      write(*,*,iomsg=message,iostat=ios)r32,r64,r128
      if(ios.ne.0)write(*,*)trim(message)
      ! hexadecimal format to show different kinds
      write(*,’(*(z0,1x))’,iomsg=message,iostat=ios)r32,r64,r128
      if(ios.ne.0)write(*,*)trim(message)
      ! G0 format
      write(*,’(*(g0,1x))’,iomsg=message,iostat=ios)r32,r64,r128
      if(ios.ne.0)write(*,*)trim(message)
      ! if a specific numeric field is used
      write(*,’(*(f3.1,1x))’,iomsg=message,iostat=ios)r32,r64,r128
      if(ios.ne.0)write(*,*)trim(message)
      ! if format is less than three characters
      write(*,’(*(f2.1,1x))’,iomsg=message,iostat=ios)r32,r64,r128
      if(ios.ne.0)write(*,*)trim(message)

      ! an option to terminate a program when a NaN is encountered
      ! (if X is NaN the comparison with 0. is always false.)
      if (.not.(r32<=0.0) .and. .not.(r32>=0.0))then
         write(*,*)’found nan’
         stop
      endif

      ALT1: block
         integer :: x = 2143289344
         print *, transfer(x, 1.0)    ! prints "nan" on i686
      endblock ALT1

   end program demo_nan

Results:

   NaN      NaN              NaN
   7FC00000 7FF8000000000000 7FFF8000000000000000000000000000
   NaN NaN NaN
   NaN NaN NaN
   ** ** **
    found nan

SEE ALSO

IS_NAN(3f)

AUTHOR

John S. Urban

LICENSE

Public Domain

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Nemo Release 3.1

nan (3)

February 23, 2025

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