TweetFollow Us on Twitter

Fortran Debugging
Volume Number:9
Issue Number:3
Column Tag:Jörg's Folder

LS Tools for FORTRAN Debugging

The easy way to avoid those bugs that make you feel foolish.

By Jörg Langowski, MacTech Magazine Regular Contributing Author

Whoever has written a more or less complicated program (and you probably wouldn’t be reading this if you hadn’t) knows that the hardest bug to find is always the next-to last (you won’t find the last one, of course). I’m using Fortran for most of my programming (and even dare to admit that): it is nice to be able to use math libraries and other existing code and put that directly on the Macintosh. But whenever I sit for days over a piece of code and just don’t see why it won’t work, only to find out that I had mixed up the order of parameters or their types in some obscure subroutine call, I start hating programming in general and Fortran in particular. In C++ types are checked: if you try to pass an integer for a real, the compiler will complain. If I only had the time to recode all my stuff into C++, I’d probably do so.

But at the moment, I’m working a lot with Fortran, like many of my colleagues. So we’d better have some good debugging aids that save us time. Language Systems has just presented a series of such tools, which I’d like to tell you about.

FLint

A typical error in languages which don’t have type checking is to pass a parameter of a wrong type to a subroutine. Look at the following example:

 program calls
 
 real*8 x
 real*8 b(50,50)
 integer n
 character*40 c
 
 call sub_a (x, b, n, c)
 write (*,*) ((b(i,j),i=1,5),j=10,15)
 
 call sub_a (b, n, x, c)
 write (*,*) ((b(i,j),i=1,5),j=10,15)
 
 end
 
 subroutine sub_a(x, b, n, c)
 
 real*8 x
 real*4 b(50,50)
 integer n

 character*40 c

 do i=1,50
 do j=1,50
 b(i,j) = i + 0.01*j
 end do
 end do
 
 return
 end

where the subroutine sub_a, which writes into the array b, is called twice from a main program. Both calls are wrong: in the first case, an array of the wrong type is passed (real*4 instead of real*8), and on the second call, the order of the parameters is completely mixed up. Of course, the output values, after the calls to sub_a, will be totally wrong.

The example is trivial, and the error in this case would be rather easy to catch. The program even ran on my machine without complaints, even though the subroutine will write half the values for b into no-man’s land, the array passed being only half as big as it should be. However, errors of this kind do happen often enough, and will be much harder to catch in a complex program than in the isolated example given here.

The interesting thing is that the compiler swallows the code without any error or warning messages. It would be nice to have a tool which will indicate if a subroutine has been called with the wrong number or type of arguments.

LSFlint, contained in the debugging toolkit for LS Fortran distributed by Language Systems, does this kind of type checking, and a lot of other things. It runs under the MPW shell; for testing the example above (in file calls.f), you might type

LSFlint calls.f

and you’ll get this output:

      call sub_a (b, n, x, c)
### lsflint - Warning - SUB_A arg   2:N, possible size discrepancy exists
### lsflint - Warning - SUB_A arg   2:N, possible type discrepancy exists
### lsflint - Warning - SUB_A arg   3:X, possible size discrepancy exists
### lsflint - Warning - SUB_A arg   3:X, possible type discrepancy exists
    File "calls.f"; Line 11
#------------------------------------------------------------
    File "calls.f"; Line 8 # earlier usage
#------------------------------------------------------------

      subroutine sub_a(x, b, n, c)
### lsflint - Warning - SUB_A arg   2:B, possible size discrepancy exists
### lsflint - Warning - SUB_A arg   2:B, possible type discrepancy exists
    File "calls.f"; Line 16
#------------------------------------------------------------
    File "calls.f"; Line 8 # earlier usage
#------------------------------------------------------------

Of course, LSFlint includes complete syntax checking, you’ll get the same syntax error messages as the compiler would give you for wrong code. It works at almost the same speed as the compiler: in my test it took 7 minutes for checking a program of a total of 4355 lines of code, while the compiler (at opt=3) took 5:30 minutes. However, in that case it created pages of warning messages (that was on a program that ran correctly!): about variables that had been declared but never used, about possible problems with passing pointers to matrices in subroutine calls, and even about some places where I had called a subroutine with the wrong number of parameters! It is actually amazing that that program gave the correct answers. This will give me now some opportunity to really ‘lint out’ that code, which is what LSFlint is all about.

An obvious area of application for LSFlint is for those who use Macintosh system calls from Fortran. You can easily make a mistake about which parameters have to be passed by value, by reference, and which are 16 or 32 bits long. All those errors will be caught by LSFlint.

Finally, if you are still using common blocks in your code (which I think is an ugly practice, especially since LS Fortran now allows named global variables), the program will detect differences in the size of common blocks and other discrepancies between routines. Also, when structures are passed to subroutines it will not only be checked whether the size and type of the elements matched, but whether the structure actually has the correct name. All in all, a very useful tool for improving Fortran code (one must mention that Lint, a similar utility for C code, has been available on the Unix scene from various sources for a long time). Still, you have to write your own code.

DebugLib

The second tool included in the LS debugging toolkit is DebugLib, a debugging library. By linking your code with DebugLib.o (it contains routines which override some of those in FORTRANLib.o), you will have interactive control over the various debugging options that Language Systems Fortran offers: until now, you would have had to recompile the program for changing those options. Now, when you have compiled a program with -debug=3 -r -ov and linked with the debugging library, a dialog appears when you execute the program that allows you to set the debugging options interactively:

Figure 1

Each time the dialog comes up, it tells you where you are in the program (top two lines), and lets you check the debugging options. The last option is especially useful; it will let the program pause (and redisplay this dialog) on each subroutine entry, when you hold down the caps lock key. Thus, by releasing the caps lock key you may accelerate your program while it is executing uncritical sections of code. There is also an option that tries to recover from stack overflow errors by increasing the stack space; this can be important if you use lots of local variables that take up space on the stack on every subroutine call. The other options should be evident; you know already the trace window from earlier versions of LS Fortran (it displays continuously the line and routine name where the program is executing).

SourceBug

Finally, the debugging toolkit contains a copy of Apple’s SourceBug, an interactive source code debugger that is much easier to use (though less powerful) than the SADE debugger. It needs a symbol file that the compiler and linker create from your application; for LS Fortran, you use the -sym option for the compiler and the -sym on option for the linker. You then open up SourceBug, and use the Open command from its File menu to start up your application. SourceBug will then open the ‘program browser’ which contains a list of all the source files that make up your program and for each source file all its routines.

You can set breakpoints in your program simply by choosing a routine with the two lists on top, and then click next to the program line where you want to have the breakpoint. Of course, SADE would give you much better control, for instance you can have conditional breakpoints; but SourceBug is very straightforward to use and needs no long setting up, like SADE.

Figure 2

You start your application by selecting ‘Run’ from a Control menu. When the program then hits the breakpoint, a second browser will come up, the ‘stack crawl’ window, which shows the routine where the break occurred and the calling sequence starting with the main program:

Figure 3

Here, you may now inspect the values of all variables simply by selecting them with the mouse and selecting ‘Evaluate’. I should say that you may find some difficulties here when you select big arrays to display; it takes forever to refresh the window which displays its values. But for simple variables or smaller arrays, it works just fine.

Other goodies

There has been more information on my desk about new Products that run with Fortran. Two tools, also available through Language Systems for some time now, are a plotting library called SuperPlot and a ‘code structurer’ that converts spaghetti code into nicely stratified lasagna. A review of these two utilities is long overdue, and I’ll try to put it into this column before long. But until then, we should also hear again about C++ and Forth.

MacForth people, please take note that we are desperately looking for good examples written for MacForth - we’d like to cover the only commercial Forth product for the Macintosh a little more than we have usually been doing (which should not be difficult).

 
AAPL
$524.94
Apple Inc.
+5.93
MSFT
$40.01
Microsoft Corpora
-0.39
GOOG
$536.10
Google Inc.
-20.44

MacTech Search:
Community Search:

Software Updates via MacUpdate

VMware Fusion 6.0.3 - Run Windows apps a...
VMware Fusion allows you to create a Virtual Machine on your Mac and run Windows (including Windows 8.1) and Windows software on your Mac. Run your favorite Windows applications alongside Mac... Read more
Tweetbot 1.5.1 - Popular iOS twitter cli...
Tweetbot is a full-featured OS X Twitter client with a lot of personality. Whether it's the meticulously-crafted interface, sounds and animation, or features like multiple timelines and column views... Read more
Mac DVDRipper Pro 4.1.7 - Copy, backup,...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
PDFpenPro 6.2 - Advanced PDF toolkit for...
PDFpenPro allows users to edit PDF's easily. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Create... Read more
PDFpen 6.2 - Edit and annotate PDFs with...
PDFpen allows users to easily edit PDF's. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Features... Read more
Monolingual 1.5.9 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. It requires a 64-bit capable Intel-based Mac and at least... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
Starcraft II: Wings of Liberty 1.1.1.180...
Download the patch by launching the Starcraft II game and downloading it through the Battle.net connection within the app. Starcraft II: Wings of Liberty is a strategy game played in real-time. You... Read more
Sibelius 7.5.0 - Music notation solution...
Sibelius is the world's best-selling music notation software for Mac. It is as intuitive to use as a pen, yet so powerful that it does most things in less than the blink of an eye. The demo includes... Read more
Typinator 5.9 - Speedy and reliable text...
Typinator turbo-charges your typing productivity. Type a little. Typinator does the rest. We've all faced projects that require repetitive typing tasks. With Typinator, you can store commonly used... Read more

Latest Forum Discussions

See All

Have a Special Dead Trigger 2 Easter Bas...
Have a Special Dead Trigger 2 Easter Basket Full of Goodies, Courtesy of Madfinger Games Posted by Rob Rich on April 18th, 2014 [ permalink ] Dead Trigger 2 | Read more »
Almost All of Playdek’s Library is on Sa...
Almost All of Playdek’s Library is on Sale Right Now, and You Should Check it Out Posted by Rob Rich on April 18th, 2014 [ permalink ] Playdek has released quite a few great iOS ports of board and card games over the years, and now most of them... | Read more »
Zynga Launches Brand New Farmville Exper...
Zynga Launches Brand New Farmville Experience with Farmville 2: Country Escape Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »
David. Review
David. Review By Cata Modorcea on April 18th, 2014 Our Rating: :: MINIMALISTIC IN A DIFFERENT WAYUniversal App - Designed for iPhone and iPad David is a minimalistic game wrapped inside of a soothing atmosphere in which the hero... | Read more »
Eyefi Unveils New Eyefi Cloud Service Th...
Eyefi Unveils New Eyefi Cloud Service That Allows Users to Share Media Across Personal Devices Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »
Tales from the Dragon Mountain: The Lair...
Tales from the Dragon Mountain: The Lair Review By Jennifer Allen on April 18th, 2014 Our Rating: :: STEADY ADVENTURINGiPad Only App - Designed for the iPad Treading a safe path, Tales from the Dragon Mountain: The Lair is a... | Read more »
Yahoo Updates Flickr App with Advanced E...
Yahoo Updates Flickr App with Advanced Editing Features and More Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »
My Incredible Body - A Kid's App to...
My Incredible Body - A Kid's App to Learn about the Human Body 1.1.00 Device: iOS Universal Category: Education Price: $2.99, Version: 1.1.00 (iTunes) Description: Wouldn’t it be cool to look inside yourself and see what was going on... | Read more »
Trials Frontier Review
Trials Frontier Review By Carter Dotson on April 18th, 2014 Our Rating: :: A ROUGH LANDINGUniversal App - Designed for iPhone and iPad Trials Frontier finally brings the famed stunt racing franchise to mobile, but how much does its... | Read more »
Evernote Business Notebook by Moleskin I...
Evernote Business Notebook by Moleskin Introduced – Support Available in Evernote for iOS Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »

Price Scanner via MacPrices.net

Deal Alert! 13-inch MacBook Pro on sale for $...
Best Buy has the 13″ 2.5GHz MacBook Pro on sale for $999.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $200 off MSRP. Price is valid... Read more
Free HopTo 2.2 Helps Enhance Your Productivit...
The HopTo app helps you do more on your iPad by providing more and easier adaccess to files and documents. Version 2.2 adds Egnyte and HopTo’s Mac OSX File Connector. If you already have the hopTo... Read more
National Distracted Driving Awareness Month:...
As the country recognizes National Distracted Driving Awareness Month, Sprint is reminding wireless consumers to focus on driving while behind the wheel, to not text or email while driving, and to... Read more
13-inch 2.4GHz Retina MacBook Pro available f...
Abt has the 13″ 2.4GHz 128GB Retina MacBook Pro available for $1229 including free shipping. Their price is $70 off MSRP. Read more
iMacs on sale for up to $160 off MSRP this we...
Best Buy has iMacs on sale for up to $160 off MSRP for a limited time. Choose free home shipping or free instant local store pickup (if available). Prices are valid for online orders only, in-store... Read more
iPad Airs on sale this weekend for up to $100...
Best Buy has WiFi iPad Airs on sale for $50 off MSRP and WiFi + Cellular iPad Airs on sale for $100 off MSRP on their online store for a limited time, with prices now starting at $449. Choose free... Read more
Apple restocks refurbished Mac minis starting...
The Apple Store has restocked Apple Certified Refurbished Mac minis for up to $150 off the cost of new models. Apple’s one-year warranty is included with each mini, and shipping is free: - 2.5GHz Mac... Read more
Hyundai Brings Apple CarPlay To The 2015 Sona...
Hyundai Motor America has announced it will bring Apple CarPlay functionality to the 2015 Sonata. CarPlay is pitched as a smarter, safer and easier way to use iPhone in the car and gives iPhone users... Read more
Updated iPads Coming Sooner Than We Had Thoug...
MacRumors, cites KGI securities analyst Ming Chi Kuo, well-respected as an Apple product prognisticator, saying that Apple will introduce an upgraded iPad Air and iPad mini in 2014/Q3, meaning the... Read more
Toshiba Unveils New High And Low End Laptop M...
Toshiba has announced new laptop models covering both the high-end and low-end of the notebook computer spectrum. Toshiba 4K Ultra HD Laptop Toshiba’s new Satellite P55t features one of the world’s... Read more

Jobs Board

Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Inc. Research Data Specialist - Appl...
…of Worldwide Market Research & Intelligence. The team is responsible for conducting Apple branded consumer market research. It is also responsible for analyzing data Read more
*Apple* Automotive Parts Department position...
Apple Automotive is one of the fastest growing dealer…and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive, we Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.