Fortran bug?

[John Chee Wah]

In article <53943 at sgi.sgi.com> bron at bronze.wpd.sgi.com (Bron Campbell Nelson) writes:
>In article <1990Mar17.021042.20480 at helios.physics.utoronto.ca>, sysjohn at physics.utoronto.ca (John Chee Wah) writes:
>> 
>> Here is a piece of code (isn't mines) that I think should work. Loops and
>> goto ends with a single continue statement. The program will work if the
>> two loops have separate statement labels.
>> System is 4D/240 with 3.2.1.
>> -----
>>       write(6,'(''Enter integer 0 or less and program will loop: '',$)')
>>       read(5,*)iup
>> c
>>       do 1 i=-1,1
>>          if(i.gt.iup)goto 1
>>          do 1 j=-1,1
>>             write(6,'(''j='',i4)')j
>>  1    continue
>> c
>>       stop
>>       end
>
>This question comes up over and over in different ways.  This is not
>really a bug in the Fortran compiler; the code as written is not standard
>conforming, and its exact meaning is ambiguous.  I admit that I think the
>compiler ought to give an error message, but it does not (and neither
>do most other Fortran compilers).
>
>The problem is that statement 1 is considered to be a statement in the
>inner loop.  When you branch to it, you have branched from an outer
>block into an inner block, which is not allowed (just as branching directly
>to the "write" statement is not allowed).  The Fortran compiler
>gets confused about whether it should "continue" back at the j loop, or
>the i loop.  In fact it goes to the inner (j) loop which has not been
>properly initialized, picks up garbage off the stack, and goes.
>
>This topic gets hashed out in comp.lang.fortran every year or so.  Many
>other Fortran compilers have similar behavior, some do it differently,
>some give a compile error.  Using separate labels for the loops is the
>right thing to do.


Definitely placing other statement labels should things clear to
others and compiler. The problem is that the code is similar to part of 
a large program that ran on VAX/VMS and on SUN (I think) and it is just
that when users (who just wants to run the programs) tries to compile
and run the program on the iris, don't understand why it does not work.
You get answers like "but it works on the VAX!"

Maybe ambiguous things like this, could be documented in the Fortran
manual.
>
>
>--
>Bron Campbell Nelson
>bron at sgi.com  or possibly  ..!ames!sgi!bron
>These statements are my own, not those of Silicon Graphics.