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Path: utzoo!utgpu!water!watmath!clyde!masscomp!danny
From: danny@masscomp.UUCP
Newsgroups: comp.lang.fortran
Subject: Re: Problem with substrings
Message-ID: <1812@masscomp.UUCP>
Date: Thu, 4-Jun-87 12:26:33 EDT
Article-I.D.: masscomp.1812
Posted: Thu Jun  4 12:26:33 1987
Date-Received: Sat, 6-Jun-87 09:36:24 EDT
References: <286@nikhefh.UUCP>
Reply-To: danny@masscomp.UUCP (Daniel Pearl)
Distribution: na
Organization: MASSCOMP - Westford, Mass. (USA)
Lines: 22

In article <286@nikhefh.UUCP> i91@nikhefh.UUCP (Fons Rademakers) writes:
>Does somebody know what according to the FORTRAN 77 standard 
>should happen in the following substring expression:
>
>        CHARACTER*10 CH, STR
>        
>	STR = 'ABCDEFGHIJ'
>        I   = 6
>        NC  = 0
>        CH  = 'FOO'//STR(I:I+NC-1)//'BAR'

Some compilers have extended to allow "null substrings"; they are
sometimes useful.  Often, a null substring is denoted by STR(start:finish)
where the value of the finish expression is start-1.  Another implementation
might say that if finish<start then the length of the substring is 0.

But according to the standard, the end value for the substring must be
less than the start value. Therefore, the program is not standard 
conforming.  What processors do with non-standard-conforming programs
is up to the processor, so the Apollo processor, although it 
produced a segmentation fault at runtime, could be called standard-
conforming (assuming it did everything else according to the standard ;-)