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.


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)
 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

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.


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).


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

Adobe Acrobat Reader 15.009.20069 - View...
Adobe Acrobat Reader allows users to view PDF documents. You may not know what a PDF file is, but you've probably come across one at some point. PDF files are used by companies and even the IRS to... Read more
Adobe Acrobat Pro 15.009.20069 - Powerfu...
Acrobat Pro DC is available only as a part of Adobe Creative Cloud, and can only be installed and/or updated through Adobe's Creative Cloud app. Adobe Acrobat Pro DC with Adobe Document Cloud... Read more
Path Finder 7.2 - Powerful, award-winnin...
Become a master of file management with Path Finder. Take full control over your file system. Save your time: compare and synchronize folders, view hidden files, use Dual Pane and full keyboard... Read more
Sid Meier's Civilization: Beyond Ea...
Sid Meier's Civilization: Beyond Earth is a new science-fiction-themed entry into the award-winning Civilization series. Set in the future, global events have destabilized the world leading to a... Read more
ForkLift 2.6.6 - Powerful file manager:...
ForkLift is a powerful file manager and ferociously fast FTP client clothed in a clean and versatile UI that offers the combination of absolute simplicity and raw power expected from a well-executed... Read more
Microsoft Remote Desktop 8.0.21 - Connec...
With Microsoft Remote Desktop, you can connect to a remote PC and your work resources from almost anywhere. Experience the power of Windows with RemoteFX in a Remote Desktop client designed to help... Read more
OnyX 3.1.0 - Maintenance and optimizatio...
OnyX is a multifunctional utility for OS X. It allows you to verify the startup disk and the structure of its System files, to run miscellaneous tasks of system maintenance, to configure the hidden... Read more
Spotify - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
ExpanDrive - Access cloud storag...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
Markly 1.5.3 - Create measurement and de...
Markly is a measurement and design-spec plugin/extension for Photoshop and Sketch. It is made for modern Web designers and app front-end developers. You can add specification marks simply by clicking... Read more

Max Ammo - Tricks and tips to help you l...
Max Ammo is a smart cover shooter in which you have to fight back against the Reptor Empire, a race of alien lizards who have invaded your home. You'll have to tap to shoot, swipe to get into cover, and upgrade your gear if you plan on surviving... | Read more »
Balls & Holes - Tips and tricks to h...
Balls & Holes is a gorgeous new endless runner that challenges you to make it as far up a mountain as possible before inevitably being sliced into a load of gooey bits. Making this task more difficult are both the wide variety of balls that... | Read more »
Balloony Land offers a fresh twist on th...
Balloony Land by Palringo offers a fresh twist on the match three genre and is out now on iOS and Android. First-off, you'll be popping balloons instead of crushing candy and the balloons will float up and fill the empty spaces instead of dropping... | Read more »
Graphic - vector illustration and design...
Graphic - vector illustration and design 1.0 Device: iOS iPhone Category: Productivity Price: $2.99, Version: 1.0 (iTunes) Description: Autodesk Graphic is a powerful full-featured vector drawing and illustration application right in... | Read more »
Sago Mini Babies (Education)
Sago Mini Babies 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: Introducing the Sago Mini babies. Boys and girls love caring for these adorable characters. Feed Robin her favorite mush... | Read more »
PAUSE - Relaxation at your fingertip (H...
PAUSE - Relaxation at your fingertip 1.1 Device: iOS iPhone Category: Healthcare & Fitness Price: $1.99, Version: 1.1 (iTunes) Description: | Read more »
Super Sharp (Games)
Super Sharp 1.1 Device: iOS Universal Category: Games Price: $1.99, Version: 1.1 (iTunes) Description: Your finger has never been so sharp! Cut with skill to complete the 120 ingenious physics levels of Super Sharp and become a cut... | Read more »
Assembly - Graphic design for everyone...
Assembly - Graphic design for everyone 1.0 Device: iOS Universal Category: Photography Price: $2.99, Version: 1.0 (iTunes) Description: Assembly is the easiest most powerful design tool on the App Store. Create anything you can... | Read more »
Dub Dash (Games)
Dub Dash 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: ARE YOU READY FOR THE ULTIMATE CHALLENGE? UNIQUE SYMBIOSIS OF MUSIC AND GRAPHICS | Read more »
Leave Me Alone (Games)
Leave Me Alone 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: 33% off launch sale!!! Somewhere between the 1980s and 1990s there exists a world that never was. A world of skatepunks,... | Read more »

Price Scanner via

Adobe and Dropbox Partner to Streamline Work...
Adobe and Dropbox Inc. have announced a partnership to enable people and organizations greater flexibility to work the way they want with documents at home, in the office or on-the-go. The companies... Read more
DriveSavers Offers Data Recovery Relief to Vi...
DriveSavers, specialists in data recovery, eDiscovery and digital forensic services have announced assistance to victims of the recent storm and historically unprecedented flooding in South Carolina... Read more
Apple Products Four Of 2015′s Top Ten Most Wa..., Future’s global technology brand and the UK’s biggest technology website, has unveiled results from extensive research that show • The Smart Home is what excites the public most about... Read more
13-inch 2.7GHz/128GB Retina MacBook Pro on sa...
Best Buy has the 13″ 2.7GHz/128GB Retina MacBook Pro on sale for $1174.99 for a limited time. Choose free shipping or free local store pickup (if available). Sale price for online orders only, in-... Read more
App Tamer 2.1 Makes El Capitan Cooler, Quiete...
St. Clair Software has announced the availability of a free update to its App Tamer utility for Mac OS X. App Tamer 2.1 delivers compatibility with Yosemite and improves its support for a number of... Read more
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has 2015 15″ Retina MacBook Pros on sale for up to $160 off MSRP including free shipping plus NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $1849.99 $150 off - 15″ 2.5GHz Retina... Read more
12-inch Retina MacBooks on sale for $100 off...
Best Buy has 12″ Retina MacBooks available for $100 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Discounted prices available for online orders only... Read more
MacBook Airs on sale for up to $100 off MSRP
Save up to $100 on the purchase of a new 2015 13″ or 11″ 1.6GHz MacBook Air at the following resellers. Shipping is free with each model: 11" 128GB MSRP $899 11" 256GB... Read more
Save 15% with Apple refurbished Mac Pros
The Apple Store has Apple Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The... Read more
Apple restocks refurbished Mac minis for up t...
Apple has restocked Certified Refurbished 2014 Mac minis, with models available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz Mac mini: $419 $... Read more

Jobs Board

*Apple* Desktop Analyst - KDS Staffing (Unit...
…work with some of the brightest engineers. Job Description Title: Apple Desktop AnalystPosition Type: Full-time PermanentLocation: White Plains, NYHot Points:Depth of Read more
*Apple* Systems Engineer (Mclean, VA and NYC...
Title: Apple Systems Engineer (Mclean, VA and NYC) Location: United States-New York-New York-NYC 200 Park Avenue (22005) Other Locations: United Read more
Partner Business Development Manager - *Appl...
…exceptional individuals to join our Sales Solutions team as Business Development Manager- Apple . This position focuses on the overall management of and achievement of Read more
Project Manager: *Apple* Pay - Apple (Unite...
…The iOS Systems team is looking for a project manager who will manage Apple Pay server side integration project resources in a matrix organization, track tasks, prepare Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, you're Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.