forums.silverfrost.com

Emanuele · Joined: 21 Oct 2009 Posts: 78 Location: Bologna (Italy)

I�m working on a fortran program which was probably developed on a system that provided automatic initialization of variables and arrays to zero. On FTN95, this program generates many arithmetic errors.

Is there a compiler option to initialize local variables and arrays (not only saved ones) to zero?

Thank you in advance for any suggestion.

LitusSaxonicum · Posted: Sun Dec 20, 2015 4:38 pm Post subject:

/ZEROISE only works on statically allocated variables, so perhaps needs to be combined with the global /SAVE compiler option.

Emanuele · Joined: 21 Oct 2009 Posts: 78 Location: Bologna (Italy)

Thank you. It could work, but I'm a bit scared of setting the global save, since there are subs that are called several times in a run.

wahorger · Joined: 13 Oct 2014 Posts: 1227 Location: Morrison, CO, USA

/SAVE means that they are not saved on the stack. A fixed address is used.

If the code is as old as you think, perhaps the code is written not to be recursive/re-entrant and /SAVE will work just fine.

/SAVE does not save the current contents, then reload the next time the code is run. You'll always start with a fresh copy.

JohnCampbell · Joined: 16 Feb 2006 Posts: 2593 Location: Sydney

Both /ZERO and /SAVE are non-conforming for Fortran 95.
Depending on how complex your code is, I would prefer to change the code to initialise all variables as they are being used.
I have not used /ZERO, but this may make the .exe much larger and also initialise arrays that might not be used if there are different options in your program.
/SAVE will also remove dynamic allocation of local variables/arrays and stop recursion.

It can be a personal preference, but I would never use /ZERO or /SAVE. I'd change the code to control where this is needed.

wahorger · Joined: 13 Oct 2014 Posts: 1227 Location: Morrison, CO, USA

John has a good point. It is ALWAYS best to do your own initialization.

When reusing old code, however, it might be a reasonable "shortcut" to use both /ZERO and /SAVE so that you can get the code working in the shortest amount of time. This is especially true if it is not your code that you are working with!

LitusSaxonicum · Posted: Mon Dec 21, 2015 11:05 am Post subject:

If it is old code, then it doesn't need to be Fortran 95 compliant, does it?

I agree that it is always best to initialise yourself, and it has been best practice to assume no initialisation and local variables don't retain their values.

Emanuele · Joined: 21 Oct 2009 Posts: 78 Location: Bologna (Italy)

Thank you everybody.

I totally agree that the right thing to do would be initializing the variables in the code when they are used. However this is a complex code and it is not mine, so modifying it would require a lot of time.

If I understand correctly what wahorger said, /save option does not preserve the values of the variables between successive calls of the routines. Can you confirm this?

mecej4 · Joined: 31 Oct 2006 Posts: 1897

Emanuele · Joined: 21 Oct 2009 Posts: 78 Location: Bologna (Italy)

Thanks and happy new year to everybody!

LitusSaxonicum · Posted: Sun Jan 03, 2016 1:34 pm Post subject:

Just asking ...

Might there be a BLOCK DATA somewhere that isn't linked in?

I can't find any of the Fortran stuff that Les Hatton used to have on his website, but I do remember that he once advocated using named BLOCK DATA routines and declaring their names in an EXTERNAL statement as a method of making sure that the linker looked for it/them. I didn't like that much, but then I don't use BLOCK DATA for historical reasons - it wasn't available on several systems I used decades ago. (Instead I have an ordinary subroutine named BLOCK_DATA that gets called for every new problem).

wahorger · Joined: 13 Oct 2014 Posts: 1227 Location: Morrison, CO, USA

BLOCK DATA would be an excellent place to look, if you have it. I've been using it since the 70's. It is the only way to initialize labeled COMMON. BLANK COMMON might be able to be initialized in a program/module, but I steer away from BLANK COMMON.

I have a large number of COMMON blocks and many, many variables. I always initialize in the BLOCK DATA sub-program.

This does make the image to be loaded larger, but that is of no real concern.

I've used /SAVE and /ZERO. I may be incorrect, but I believe that /ZERO does not work for variables in BLANK or labeled COMMON. That is my experience, as I've been compiling in /CHECKMATE mode and had Undefined errors at run-time when referencing COMMON.

JohnCampbell · Joined: 16 Feb 2006 Posts: 2593 Location: Sydney

I've been wondering how BLOCK DATA will work with FTN95 /64. In /64, SLINK64 allocates common a memory address at startup (which is fantastic as it removes the 2gb common size limitation) but I wonder what it does for BLOCK DATA initialised common ?

I can't recall a program I have developed that uses BLOCK DATA. I initialise most variables at run time, except for local variables/parameters that are in a data statement. For example I will typically code:
" LOGICAL :: first_call = .true. "
and utilise this as an indicator of first or subsequent calls.

Doesn't /ZERO make the .obj and .exe much larger ? May be when disk space was at a premium I developed a dislike for /ZERO.

I still avoid some code structures where there were bugs in earlier versions of FTN95. I've long tried to develop a safe coding style and it's hard to change. I probably once used a linker that had restrictions using BLOCK DATA. Many early compilers I used did not provide /Zero and I think Salford FTN77 on Pr1me was the first time I saw /zero.

John

PaulLaidler · Posted: Mon Jan 04, 2016 8:34 am Post subject:

Here is an extract from the 64 bit beta installation notes...

LitusSaxonicum · Posted: Mon Jan 04, 2016 10:53 am Post subject:

Paul,

I assume that the space for COMMON blocks is allocated when a program starts, but thereafter the allocation is static for the whole program run.

John,

I liked your first_call idea, and decided that I would use it myself, until I realised that if I start a program with File | New I automatically initialise everything, and if I start from File | Open or a file association (I don't do 'drag and drop') then I initialise in a different way. I only use single document interfaces (SDI) so I know at any point (as if it isn't obvious from where in the program it is) from the grey codes in the File menu whether it is a 'start from nothing' run or not.