Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!clarkson!sun.soe.clarkson.edu!taylor
Date: Tue, 2 Apr 91 08:07:21 EST
From: Ross Taylor <taylor@sun.soe.clarkson.edu>
Message-Id: <9104021307.AA25164@sun.soe.clarkson.edu>
Subject: Re: Checking a string for an integer
Newsgroups: comp.lang.fortran


Here's my contribution to this discussion: two routines for converting
strings of any length to integers or real numbers.  there are no
read statements and as far as I know the code is completely standard
F77.

Ross Taylor
Department of Chemical Engineering
Clarkson University
Potsdam, NY 13699 (yes, we have our own zip code)

taylor@sun.soe.clarkson.edu

C     *******************************************************************
C     *                                                                 *
C     *    SUBROUTINE CHRTOI                                            *
C     *                                                                 *
C     *******************************************************************
C
      SUBROUTINE CHRTOI (INT, STRING, IERR)
C
C     Function
C     --------
C
C        To return an integer stored as a character string
C
C     Arguments
C     ---------
C
C        INT     - The integer in numeric form (output)
C        STRING  - The character string (input)
C        IERR    - Error flag set to 1 if non-numeric character found
C
C     Remarks
C     -------
C
C        Code written by ross taylor, delft, march 7, 1988
C        Inspired by code written by malcolm woodman
C
      CHARACTER*(*) STRING
C
C     Initialize integer
C
      INT  = 0
      IERR = 0
C
C     Determine length of character string
C
      LENGTH = LEN(STRING)
C
C     Check for sign in position 1
C
      L1 = 1
      IF (STRING(1:1) .EQ. '-' .OR. STRING(1:1) .EQ. '+') L1 = 2
      L2 = LENGTH + L1
C
      DO 1 I = L1, LENGTH
C
         K = L2 - I
C
C     Starting from the last character
C     Convert to integer (ichar returns ascii code) (0 = 48; 9 = 57)
C
         KK = ICHAR (STRING(K:K)) - 48
C
C     Check for non-numeric characters
C
         IF (KK .LT. 0 .OR. KK .GT. 9) THEN
            INT  = 0
            IERR = 1
            RETURN
         ENDIF
C
C     Add current contribution to int
C
         INT = INT + KK * 10 ** (I-L1)
C
    1 CONTINUE
C
      IF (STRING(1:1) .EQ. '-') INT = - INT
C
      RETURN
      END
C
C     *******************************************************************
C     *                                                                 *
C     *    subroutine chrtor                                            *
C     *                                                                 *
C     *******************************************************************
C
      SUBROUTINE CHRTOR (REAL, STRING, IERR)
C
C     Function
C     --------
C
C        To return a real number stored as a character string
C
C     Arguments
C     ---------
C
C        REAL    - The number in numeric form    (output)
C        STRING  - The character string          (input)
C        IERR    - Error flag set to 1 if non-numeric character found
C
C     Remarks
C     -------
C
C        This subroutine works by breaking up the input character string
C        Into three segments: the integer part, the decimal part and the
C        Exponent.  subroutine chrtoi is used to convert all three
C        Character strings to intgers and the results combined to give the
C        Real number output
C
C        This code written by ross taylor, delft, march 8, 1988
C        Inspired by code written by malcolm woodman
C
C     Notation
C     --------
C
C        INT    - The value of the integer contribution
C        IEXP   - The exponent
C        IDEC   - The decimal contribution
C        IERR   - Error flag set to unity if non-numeric character found
C        ISTART - Location in string of first character of current part
C
C         The following character strings all give the same result
C
C         10   10.  10.0   10.d0   10d0  1d1       =       10.0
C
C
      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
C
      CHARACTER*(*) STRING
C
C     Initialize various items
C
      INT    = 0
      IDEC   = 0
      IEXP   = 0
      IERR   = 0
      ISTART = 1
      REAL   = 0.D0
C
C     Determine length of input character string
C
      LENGTH = LEN(STRING)
C
C     Look for decimal point to mark end of integer part
C
      IPOINT = INDEX(STRING,'.')
C
C     Look for 'd' or 'e' to mark exponent
C
      IPEXP = INDEX(STRING,'D')
C
      IF (IPEXP .EQ. 0) IPEXP = INDEX(STRING,'E')
      IF (IPEXP .EQ. 0) IPEXP = INDEX(STRING,'d')
      IF (IPEXP .EQ. 0) IPEXP = INDEX(STRING,'e')
C
C     Convert character string to integer
C
      IF (IPOINT .NE. 0) THEN
         CALL CHRTOI (INT, STRING(ISTART:IPOINT-1), IERR)
      ELSE IF (IPEXP .NE. 0) THEN
         CALL CHRTOI (INT, STRING(ISTART:IPEXP-1), IERR)
      ELSE
         CALL CHRTOI (INT, STRING(ISTART:LENGTH), IERR)
      ENDIF
C
      IF (IERR .NE. 0) THEN
          REAL = 0.D0
          RETURN
      ENDIF
C
      REAL = DBLE(INT)
C
C     Next, the decimal part of the result
C
      IF (IPOINT .NE. 0) THEN
C
         ISTART = IPOINT + 1
C
C     Determine length of decimal part
C
         IF (IPEXP .GT. IPOINT) THEN
            LENDEC = IPEXP - IPOINT
         ELSE
            LENDEC = LENGTH - IPOINT
         ENDIF
C
C     Convert character string to integer
C
         IF (LENDEC .GT. 0) THEN
            CALL CHRTOI (IDEC,STRING(ISTART:ISTART+LENDEC-1),IERR)
         ENDIF
C
         IF (IERR .NE. 0) THEN
             DEC = 0.D0
         ENDIF
C
         DEC = DBLE(IDEC) / 10.0 ** LENDEC
C
         IF (STRING(1:1) .EQ. '-') THEN
            REAL = REAL - DEC
         ELSE
            REAL = REAL + DEC
         ENDIF
C
      ENDIF
C
C     Finally, the exponent (if present)
C
      IF (IPEXP .GT. 0) THEN
C
         ISTART = IPEXP + 1
C
C     Convert character string to integer
C
         CALL CHRTOI (IEXP,STRING(ISTART:LENGTH),IERR)
C
         IF (IERR .NE. 0) THEN
            IEXP = 0
            RETURN
         ENDIF
C
         REAL = REAL * 10.D0 ** IEXP
C
      ENDIF
C
      RETURN
      END