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).

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Duplicate Annihilator 5.7.5 - Find and d...
Duplicate Annihilator takes on the time-consuming task of comparing the images in your iPhoto library using effective algorithms to make sure that no duplicate escapes. Duplicate Annihilator... Read more
BusyContacts 1.0.2 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
Capture One Pro 8.2.0.82 - RAW workflow...
Capture One Pro 8 is a professional RAW converter offering you ultimate image quality with accurate colors and incredible detail from more than 300 high-end cameras -- straight out of the box. It... Read more
Backblaze 4.0.0.872 - Online backup serv...
Backblaze is an online backup service designed from the ground-up for the Mac.With unlimited storage available for $5 per month, as well as a free 15-day trial, peace of mind is within reach with... Read more
Little Snitch 3.5.2 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
Monolingual 1.6.4 - 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. If you use your computer in only one (human) language, you... Read more
CleanApp 5.0 - Application deinstaller a...
CleanApp is an application deinstaller and archiver.... Your hard drive gets fuller day by day, but do you know why? CleanApp 5 provides you with insights how to reclaim disk space. There are... Read more
Fantastical 2.0 - Create calendar events...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event details... Read more
Cocktail 8.2 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Direct Mail 4.0.4 - Create and send grea...
Direct Mail is an easy-to-use, fully-featured email marketing app purpose-built for OS X. It lets you create and send great looking email campaigns. Start your newsletter by selecting from a gallery... Read more

These are All the Apple Watch Apps and G...
The Apple Watch is less than a month from hitting store shelves, and once you get your hands on it you're probably going to want some apps and games to install. Fear not! We've compiled a list of all the Apple Watch apps and games we've been able to... | Read more »
Appy to Have Known You - Lee Hamlet Look...
Being at 148Apps these past 2 years has been an awesome experience that has taught me a great deal, and working with such a great team has been a privilege. Thank you to Rob Rich, and to both Rob LeFebvre and Jeff Scott before him, for helping me... | Read more »
Hands-On With Allstar Heroes - A Promisi...
Let’s get this out of the way quickly. Allstar Heroes looks a lot like a certain other recent action RPG release, but it turns out that while it’s not yet available here, Allstar Heroes has been around for much longer than that other title. Now that... | Read more »
Macho Man and Steve Austin Join the Rank...
WWE Immortals, by Warner Bros. Interactive Entertainment and WWE, has gotten a superstar update. You'll now have access to Macho Man Randy Savage and Steve Austin. Both characters have two different versions: Macho Man Randy Savage Renegade or Macho... | Read more »
Fearless Fantasy is Fantastic for the iF...
I actually had my first look at Fearless Fantasy last year at E3, but it was on a PC so there wasn't much for me to talk about. But now that I've been able to play with a pre-release version of the iOS build, there's quite a bit for me to talk... | Read more »
MLB Manager 2015 (Games)
MLB Manager 2015 5.0.14 Device: iOS Universal Category: Games Price: $4.99, Version: 5.0.14 (iTunes) Description: Guide your favorite MLB franchise to glory! MLB Manager 2015, officially licensed by MLB.com and based on the award-... | Read more »
Breath of Light (Games)
Breath of Light 1.0.1421 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.1421 (iTunes) Description: Hold a quiet moment. Breath of Light is a meditative and beautiful puzzle game with a hypnotic soundtrack by... | Read more »
WWE WrestleMania Tags into the App Store
Are You ready to rumble? The official WWE WrestleMania app, by World Wrestling Entertainment, is now available. Now you can get all your WrestleMania info in one place before anyone else. The app offers details on superstar signings, interactive... | Read more »
Bio Inc's New Expansion is Infectin...
Bio Inc., by DryGin Studios, is the real time strategy game where you infect a human body with the worst virus your evil brain can design. Recently, the game was updated to add a whole lot of new features. Now you can play the new “Lethal”... | Read more »
The Monocular Minion is Here! Despicable...
Despicable Me: Minion Rush, by Gameloft, is introducing a new runner to the mix in their latest update. Now you can play as Carl, the prankster minion. Carl has a few new abilities to play with, including running at a higher speed from the start.... | Read more »

Price Scanner via MacPrices.net

13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.... Read more
Save up to $80 on iPad Air 2s, NY tax only, f...
 B&H Photo has iPad Air 2s on sale for $80 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469.99 $30 off - 64GB iPad Air 2 WiFi: $549.99 $50 off - 128GB iPad... Read more
iMacs on sale for up to $205 off MSRP
B&H Photo has 21″ and 27″ iMacs on sale for up to $205 off MSRP including free shipping plus NY sales tax only: - 21″ 1.4GHz iMac: $1019 $80 off - 21″ 2.7GHz iMac: $1189 $110 off - 21″ 2.9GHz... Read more
Färbe Technik Offers iPhone Battery Charge LI...
Färbe Technik, which manufactures and markets of mobile accessories for Apple, Blackberry and Samsung mobile devices, is offering tips on how to keep your iPhone charged while in the field: •... Read more
Electronic Recyclers International CEO Urges...
Citing a recent story on CNBC about concerns some security professionals have about the forthcoming Apple Watch, John Shegerian, Chairman and CEO of Electronic Recyclers International (ERI), the... Read more
Save up to $380 with Apple refurbished iMacs
The Apple Store has Apple Certified Refurbished iMacs available for up to $380 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 27″ 3.5GHz 5K iMac – $2119 $... Read more
Mac minis on sale for up to $75 off, starting...
MacMall has Mac minis on sale for up to $75 off MSRP including free shipping. Their prices are the lowest available for these models from any reseller: - 1.4GHz Mac mini: $459.99 $40 off - 2.6GHz Mac... Read more
College Student Deals: Additional $50 off Mac...
Take an additional $50 off all MacBooks and iMacs at Best Buy Online with their College Students Deals Savings, valid through April 11, 2015. Anyone with a valid .EDU email address can take advantage... Read more
Mac Pros on sale for up to $260 off MSRP
B&H Photo has Mac Pros on sale for up to $260 off MSRP. Shipping is free, and B&H charges sales tax in NY only: - 3.7GHz 4-core Mac Pro: $2799, $200 off MSRP - 3.5GHz 6-core Mac Pro: $3719.99... Read more
13-inch 2.5GHz MacBook Pro on sale for $100 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more

Jobs Board

DevOps Software Engineer - *Apple* Pay, iOS...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional Read more
Lead *Apple* Solutions Consultant - Retail...
**Job Summary** Job Summary The Lead ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store Read more
*Apple* Pay - Site Reliability Engineer - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.