Evaluating a specific letter of a string defined in a derived type in Fortran90 [duplicate]

问题

This question already has answers here:

Extract substring of Fortran string array (3 answers)

Extract a single character from a Fortran string (1 answer)

Access character at specific index in a string in Fortran (1 answer)

Closed 1 year ago.

I would like to evaluate if the 3rd letter of variable myline is 'C' or not.

I try this:

program main

    implicit none

    type line
        integer                     :: count    = 5
        character(len=48)           :: list     = 'ABCDE'
    end type

    type(line)                      :: myline
    character(len=1)                :: letter   = 'C'

    write(*,*) myline%count, myline%list

    if(myline%list(3) == letter) then
        write(*,*) 'TRUE'
    else
        write(*,*) 'FALSE'
    end if

end program

But I get:

$ /usr/local/bin/gfortran8 -mcmodel=medium -fcheck=all -Wl,-rpath=/usr/local/lib/gcc8 -o test test.f90
test.f90:15:15:

  if(myline%list(3) == letter) then
               1
Error: Syntax error in IF-expression at (1)
test.f90:17:5:

  else
     1
Error: Unexpected ELSE statement at (1)
test.f90:19:4:

  end if
    1
Error: Expecting END PROGRAM statement at (1)

I am using gfortran (gcc8) and the Fortran 90 standard.

回答1:

In Fortran, a character substring reference always needs a start and end position. So what you want here is myline%list(3:3).

You can omit the end position (retaining the colon), for example (3:), and that means the rest of the string. Similarly you can omit the start position and it means from the first character (:3).

As a suggestion, letter would be better declared with the parameter attribute as it is a constant, but what you have would work.

来源：https://stackoverflow.com/questions/57898173/evaluating-a-specific-letter-of-a-string-defined-in-a-derived-type-in-fortran90

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fortran

gfortran

fortran90