Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!usc!elroy.jpl.nasa.gov!ames!amdahl!key!sjc
From: sjc@key.COM (Steve Correll)
Newsgroups: comp.sys.mips
Subject: Re: Fortran compiler bug?
Summary: The program is illegal
Message-ID: <1933@key.COM>
Date: 28 May 90 02:49:06 GMT
References: <149@snll-arpagw.UUCP>
Distribution: na
Organization: Key Computer Labs, Fremont, CA
Lines: 70

In article <149@snll-arpagw.UUCP>, dandy@snll-arpagw.UUCP (David Dandy) writes:
> 
>       SUBROUTINE SKTEST ( LOUT, LINE, ILEN )
>       IMPLICIT DOUBLE PRECISION ( A-H, O-Z ), INTEGER ( I-N )
>       CHARACTER LINE*(*)
>       WRITE (LOUT, '(A)')
>      1    'Error in SKSNUM...'//LINE(:ILEN)//' not found...'
>       RETURN
>       END
> 
> produces the following from the compiler:
>   Error on line 4 of sktest.f: impossible element in concatenation.
> 
> I'm confused because
>   1.  "Fortran 77: Principles of Programming" by J. L. Wagener (pp. 323-
>       325) discusses this as a valid Fortran77 statement.
>   2.  This code compiles without error using VAX/VMS F77 compilers, 
>       UNICOS CFT77 compilers, and Sun release 4.0 f77 compilers.
>       (And probably others--these are the only three I tried.)
> 
> Whether or not this is a bug with the MIPS 2.1 compiler, I have to admit
> that I don't know what the WRITE statement is supposed to be doing (even
> afters reading Wagener's explanation).  Does anyone know a work-around...

The program is telling the compiler to print 'Error in SKSNUM...', followed by
the first ILEN characters of the string variable named "LINE", followed by
' not found...'. I believe the program is illegal because section 6.2.2 on page
6-8 of the ANSI X3.9-1978 "Fortran 77" standard says:

  Except in a character assignment statement (10.4), a character expression
  must not involve concatenation of an operand whose length specification is
  an asterisk in parentheses (8.4.2) unless the operand is the symbolic name
  of a constant.

For good measure, section 15.5.3 on page 15-9 says:

  A character dummy argument whose length specification is an asterisk in
  parentheses must not appear as an operand for concatenation, except in a
  character assignment statement (10.4).

This funny restriction is meant to relieve the compiler of the burden of
allocating temporary storage dynamically (it needs a temporary place to copy
the concatenated strings into, and 'ILEN' is not known at compilation time).

Wagener might claim the use of the substring "(:ILEN)" makes his code legal,
but I don't buy that, since "line", "line(:)", and "line(:len(line))" are
supposed to be identical, and clearly those substrings don't make the
 compiler's task any different.

Anyway, all is not lost. Try the following workaround, which is perfectly
legal Fortran 77:

	write(lout, '(3a)') 'Error in SKSNUM', line(:ilen),
       1    'not found...'

If you really must concatenate the strings, you can do it legally by creating
your own temporary, though you must anticipate the maximum length you will ever
need:

	subroutine sktest(lout, line, ilen)
        character*(*) line, head, tail
        integer tmpsiz
        parameter (head='Error in SKSNUM...',tail=' not found...')
        parameter (tmpsiz=256)
        character temp*(tmpsiz)
        temp = head // line(:ilen) // tail
        write(lout, '(a)') temp(1:len(head)+ilen+len(tail))
        end
-- 
...{sun,pyramid}!pacbell!key!sjc 				Steve Correll