C Library Functions - isnumber (3)

NAME

isnumber(3f) - [M_strings:TYPE] determine if a string represents a number (LICENSE:PD)

Synopsis
Description
Options
Returns
Examples
Author
License

SYNOPSIS

function isnumber(str,msg)

    character(len=*),intent(in)                       :: str
    character(len=:),intent(out),allocatable,optional :: msg

DESCRIPTION

ISNUMBER(3f) returns a value greater than zero if the string represents a number, and a number less than or equal to zero if it is a bad number. Blank characters are ignored.

OPTIONS

str the string to evaluate as to whether it represents a numeric value or not

msg An optional message describing the string

RETURNS

isnumber
the following values are returned

1 for an integer
[-+]NNNNN

2 for a whole number
[-+]NNNNN.

3 for a real value
[-+]NNNNN.MMMM

4 for a exponential value
[-+]NNNNN.MMMM[-+]LLLL [-+]NNNNN.MMMM[ed][-+]LLLL

values less than 1 represent an error

EXAMPLES

As the example shows, you can use an internal READ(3f) along with the IOSTAT= parameter to check (and read) a string as well.

    program demo_isnumber
    use M_strings, only : isnumber
    implicit none
    character(len=256)           :: line
    real                         :: value
    integer                      :: ios1, ios2
    integer                      :: answer
    character(len=256)           :: message
    character(len=:),allocatable :: description
       write(*,*)’Begin entering values, one per line’
       do
          read(*,’(a)’,iostat=ios1)line
          !
          ! try string as number using list-directed input
          line=’’
          read(line,*,iostat=ios2,iomsg=message) value
          if(ios2 == 0)then
             write(*,*)’VALUE=’,value
          elseif( is_iostat_end(ios1) ) then
             stop ’end of file’
          else
             write(*,*)’ERROR:’,ios2,trim(message)
          endif
          !
          ! try string using isnumber(3f)
          answer=isnumber(line,msg=description)
          if(answer > 0)then
             write(*,*) &
             & ’ for ’,trim(line),’ ’,answer,’:’,description
          else
             write(*,*) &
             & ’ ERROR for ’,trim(line),’ ’,answer,’:’,description
          endif
          !
       enddo
    end program demo_isnumber

Example run

   > Begin entering values
   > ERROR:          -1 End of file
   >  ERROR for            -1 :null string
   >10
   > VALUE=   10.0000000
   >  for 10            1 :integer
   >20
   > VALUE=   20.0000000
   >  for 20            1 :integer
   >20.
   > VALUE=   20.0000000
   >  for 20.            2 :whole number
   >30.1
   > VALUE=   30.1000004
   >  for 30.1            3 :real number
   >3e1
   > VALUE=   30.0000000
   >  for 3e1            4 :value with exponent
   >1-2
   > VALUE=   9.99999978E-03
   >  for 1-2            4 :value with exponent
   >100.22d-4
   > VALUE=   1.00220004E-02
   >  for 100.22d-4            4 :value with exponent
   >1--2
   > ERROR:        5010 Bad real number in item 1 of list input
   >  ERROR for 1--2           -5 :bad number
   >e
   > ERROR:        5010 Bad real number in item 1 of list input
   >  ERROR for e           -6 :missing leading value before exponent
   >e1
   > ERROR:        5010 Bad real number in item 1 of list input
   >  ERROR for e1           -6 :missing leading value before exponent
   >1e
   > ERROR:        5010 Bad real number in item 1 of list input
   >  ERROR for 1e           -3 :missing exponent
   >1e+
   > ERROR:        5010 Bad real number in item 1 of list input
   >  ERROR for 1e+           -4 :missing exponent after sign
   >1e+2.0
   > ERROR:        5010 Bad real number in item 1 of list input
   >  ERROR for 1e+2.0           -5 :bad number

AUTHOR

John S. Urban

LICENSE

Public Domain

Nemo Release 3.1

isnumber (3)

June 29, 2025

Generated by manServer 1.08 from bd1a695e-afde-438c-9710-3cf2b978988c using man macros.

str	the string to evaluate as to whether it represents a numeric value or not
msg	An optional message describing the string