Fortran: convert character array to integer/real

Question

I want to convert a character array in Fortran to a numeric type. I think I should avoid strings (perhaps not?), because these arrays store variable length data (user input).

I have the following code:

IMPLICIT NONE

CHARACTER(LEN=1), ALLOCATABLE :: TOKENS(:, :)
CHARACTER(LEN=1)              :: TEST_STR(80)
INTEGER                       :: I
CHARACTER(LEN=80)             :: INPUT_STR
INTEGER                       :: MYINT

INPUT_STR = '  I am a  test  12  string '
DO I = 1, LEN(INPUT_STR)
   TEST_STR(I) = INPUT_STR(I:I)
END DO

CALL TOKENIZE(TEST_STR, ' ', TOKENS)

PRINT *, "-----------"
INPUT_STR = '15'
PRINT *, INPUT_STR(1:2)
READ(INPUT_STR(1:2), '(I2)') MYINT
PRINT *, MYINT
PRINT *, "-----------"
PRINT *, TOKENS(:, 5)
READ(TOKENS(:, 5), '(I2)') MYINT
PRINT *, MYINT

The output looks like this:

 -----------
 15
          15
 -----------
 12
           1

I have tested separately that the tokenizer presents sane output, which it does. However, it seems that READ(TOKENS(:, 5), '(I2)') MYINT is only reading the first element of TOKENS(:, 5).

As a test, I ran it with READ(TOKENS(1, 5), '(I2)') MYINT and READ(TOKENS(2, 5), '(I2)') MYINT, and it printed 1 and 2 respectively.

Any ideas on how I can get it to read the whole array, rather than just one character at a time?

sajad abbasi · Accepted Answer · 2017-11-21 21:46:21Z

2

This is an example of converting a string to real(float) and reverse.

p.s. (10) and ! are not F77 compatible

Character(10) :: string
Real :: x, y
x = 53.65
write( string, '(f10.2)' )  x ! writes 53.65 into the string
read( string, '(f10.0)' )  y  ! reads the value from string and assigns it to y as real (float)
End

answered Nov 21, 2017 at 21:46

sajad abbasi

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Vladimir F Героям слава · Accepted Answer · 2015-03-26 20:06:22Z

1

In this line

  READ(TOKENS(:, 5), '(I2)') MYINT

you try to read from an internal file, which is an array of characters.

However, Fortran uses one character string for the internal read of each record. Therefore it reads from the first element of your array, which is a character string of length one.

You need to use strings in this part of the code, not an array ofsingle characters.

For example, if you could live with a fixed maximum character length, you could use

CHARACTER(LEN=80), ALLOCATABLE :: TOKENS(:)

You could also use

CHARACTER(LEN=:), ALLOCATABLE :: TOKENS(:)

to change the character length as needed. However, all characters in this array need to be of the same length anyway.

The last resort would be to use array of some containers which have an allocatable string component inside, but be aware that gfortran did not support these as of version 4.8 at least.

edited Mar 26, 2015 at 20:06

answered Mar 26, 2015 at 17:17

Vladimir F Героям слава

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3 Comments

Kyle_S-C Over a year ago

Thanks Vladimir. In the meantime I had discovered deferred-length strings. However, backwards compatibility is important in our group and that seems to include supporting old compilers. I've implemented your former approach, since this is used to read our input file, which shouldn't (I hope!) contain tokens over 80 characters.

Vladimir F Героям слава Over a year ago

I use something similar for the same purpose. I just use some much larger length to be safe.

Vladimir F Героям слава Over a year ago

Ok, I should have specified it more carefully. I meant it for reading one number, which always happens from a single record. I hope.

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