(j3.2006) Reallocation and dangling pointers

[Bill Long]

On Apr 16, 2015, at 3:26 PM, Tom Clune <Thomas.L.Clune at nasa.gov> wrote:

> 
> On Apr 16, 2015, at 4:16 PM, Van Snyder <Van.Snyder at jpl.nasa.gov> wrote:
> 
>> Tom mentioned the case of an allocatable target being reallocated during
>> intrinsic assignment to a whole array, thereby undefining pointers
>> associated with it.  The same problem occurs if the variable is
>> polymorphic, no matter whether it?s a scalar or an array.
> 
> Yes.
> 
>> 
>> Processors could warn that this might happen, either at a declaration
>> where a variable gets both the ALLOCATABLE and TARGET attributes, or at
>> assignments where the reallocation might occur.
>> 
>> We could in principle revise the standard to turn off automatic
>> reallocation if the variable has the TARGET attribute.  Do we favor
>> array shape and dynamic type safety more, or do we favor pointer
>> association status more?
> 
> This change would break ?many? existing codes.   
> 
> I think Malcolm?s points about the availability of workarounds settles this matter from my pov.   My job now becomes to convince all the vendors to implement the equivalent of -C=dangle.  :-)


Or, more likely, to convince your customer to use the NAG compiler as a standard-conformance checker and debugging tool.  Some sites install NAG specifically for this purpose.  It is a more comprehensive tool than other compilers (or, indeed, actual debuggers) in this area.  (Rumor has it that one of the employees knows the standard pretty well. :) )

Cheers,
Bill




> 
> - Tom
> 
> 
> 
>> 
>> 
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> 
> Thomas Clune, Ph. D. 				<Thomas.L.Clune at nasa.gov>
> Head ASTG,Code 606
> NASA GSFC		
> MS 610.8 B33-C128
> Greenbelt, MD 20771
> 301-286-4635
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Bill Long                                                                       longb at cray.com
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