Debugging ObjectARX: Break on Exception

I have presented a class entitled High Octane ObjectARX at Autodesk University the past two years. In 2006 the focus was on project organization, and last year I focused more on techniques for supporting multiple versions of AutoCAD with a single Visual Studio solution, touching briefly on testing and profiling. For 2008 I plan to focus on debugging.

To get you in the mood, I decided to blog about a capability of Visual Studio that often goes unnoticed and unused: breaking on an exception. This works just like breaking on a code breakpoint, except the debugger breaks execution *before* the exception handler gets control, thus allowing you to get a clearer picture of what was happening immediately before the exception occurred.

In an ObjectARX project, all kinds of exceptions can occur. Sometimes they are perfectly normal exceptions caused by and handled by AutoCAD. Many times, especially during development, your code triggers an exception that causes AutoCAD to crash, and it’s not obvious what caused things to go haywire.

When unexpected things happen while running your code under the debugger, the first order of business is to inspect the debug output window to determine what happened. The debug output window (Debug->Windows->Output) displays a message whenever an exception occurs. Sometimes a series of exceptions occur, usually all caused by the same root problem. Breaking when the first exception occurs will likely yield the most useful information about the cause.

Once you examine the debug output window to determine the type of exception that occurred, open the Exceptions dialog (Debug->Exceptions) and tell Visual Studio to break when the exception is thrown:

Visual Studio contains a prepopulated list of common exceptions to choose from, or you can add new ones if you need to break on an exception that is not already listed. Many times, breaking when the exception is thrown allows you to inspect the stack trace to determine which one of your functions is to blame — and in the vast majority of cases, it will be your code that is at fault!

VC Build Hook utility for Visual Studio 2008

The new Visual Studio 2008 has been released, and to celebrate, I’ve updated VC Build Hook. The updated utility allows you to use the new IDE while still building with older versions of the build tools.

Why is this necessary? If you build your AutoCAD 2007/2008 ObjectARX application with the Visual C/C++ 9.0 tools, AutoCAD will display a warning message about an incompatible module when you try to load it. You can use VC Build Hook to target all previous AutoCAD versions from a single Visual Studio 2008 solution (if you have the correct version of Visual C/C++ installed alongside Visual Studio 2008).

In my testing so far, existing Visual Studio 2005 projects build without problems in Visual Studio 2008 when VC Build Hook is installed and the new ‘BuildToolVersion’ property is set to the correct version.

Visual Studio Build Configuration Tip

I’ve received several emails recently from users of my VC Build Hook utility that mention switching the ‘UseVC7Paths’ setting on and off depending on the build configuration they are working on. If you are doing this, you need to change your project structure!

Build configurations in Visual Studio 6 and later are logically attached to the solution, not to an individual project as they were in older Visual Studio versions. What happens is that programmers find it easy to add a new build configuration to an existing ObjectARX wizard created project for targeting a new release of AutoCAD — unfortunately those configurations end up belonging to the entire solution instead of just one project. Since VC Build Hook cannot be set on a per-configuration basis, they end up having to change the project setting depending on which configuration they are building. That’s bad, very bad!

The correct way to handle this situation is to create new projects, not new build configurations. Yes, it’s a bit more work, and it would be nice if Microsoft added an easy way to clone a project, but them’s the breaks. Targeting different AutoCAD releases requires project-level changes, so you must create a new project instead of trying to get by with a new build configuration. You can and should share source code files between the projects, however.

When I create a new multi-target solution that e.g. targets AutoCAD 2000 – AutoCAD 2008, I structure the project files on my hard drive like this:

Solution (.sln file)
ARXProject (ARX module source files)
 +ARXProject.15 (.vcproj file)
 +ARXProject.16 (.vcproj file)
 +ARXProject.17 (.vcproj file)
DBXProject (DBX module source files)
 +DBXProject.15 (.vcproj file)
 +DBXProject.16 (.vcproj file)
 +DBXProject.17 (.vcproj file)

When starting a new project, I first use the wizard to create a default project structure and source code files for the current AutoCAD release. Once I’ve got that set up the way I want (including moving the project file into a subdirectory and modifying the source file paths appropriately, as well as setting the _ACADTARGET preprocessor macro), I clone projects by copying the .vcproj files and editing the copies in a text editor to give them a new GUID, then recreate my solution’s project structure from scratch by dragging and dropping the project files back into the solution and editing them as necessary.

If you need to target multiple AutoCAD releases from a single project, invest the time to set your solution up this way (and follow the other advice on my ARX tips page!), otherwise you will find yourself constantly fighting the system.

My ManuSoft manifest manifesto

With the advent of Visual Studio 2005 and automatically generated manifest files, the topic of when and how to use manifest files comes up occasionally. Since a default ObjectARX wizard generated project in Visual Studio 2005 generates an embedded manifest by default, most people don’t even think about it. Of course that was the whole idea — the manifest would ensure that the correct dependent DLLs get loaded, and voila, no *need* to think about it. One of my programming axioms applies in this case: TANSTAAFL.

The problem is that ObjectARX applications are not in charge. AutoCAD is in charge, and it will decide which VC runtime and MFC runtime DLLs to load. If your ObjectARX application loads a different VC or MFC runtime than the ones AutoCAD is using, you’ll encounter big problems. I’ve always advised disabling the manifest completely (see my ObjectARX Tips page) to avoid such a possibility. Unfortunately, there’s a catch.

The problem is that linking to the ATL80.DLL file isn’t possible by just disabling the manifest and doing nothing more. ATL is now a side-by-side (SxS) assembly, and it no longer lives on the Windows support path, so a standard un-manifested DLL won’t be able to find it. The preferred solution is to link statically to ATL (see Configuration -> General -> ‘Use of ATL’ in VS 2005 project properties) and avoid the problem altogether. If you only have one module that uses ATL, this is always the best solution.

The less desirable solution is to add a *manually-created* manifest that specifies the desired ATL SxS assembly, but ignores the VC and MFC runtime DLLs. You’ll still need to decide whether to make ATL shared or private, and in either case you *must* distribute ATL with your application to ensure that it is available when your application is deployed. You can cheat, and let VS generate your manifest file (instruct it to *not* embed the file), then just edit the resulting .manifest file to remove references to the VC and MFC assemblies. For example, here’s one that I generated (you’ll need to generate your own to ensure that the manifest matches the version you are redistributing):

<?xml version=”1.0″ encoding=”UTF-8″ standalone=”yes”?>
<assembly xmlns=”urn:schemas-microsoft-com:asm.v1″ manifestversion=”1.0″>
<assemblyidentity type=”win32″ name=”Microsoft.VC80.ATL” version=”8.0.50727.762″ processorarchitecture=”x86″ publickeytoken=”1fc8b3b9a1e18e3b”>

In my work, I’ve had very little need for manifests. The VC optimizer is able to strip the unused portions of statically linked ATL out of your code, leaving a much smaller footprint than the entire assembly would require. This eliminates the need to redistribute ATL with your application, thus reducing the overall potential for deployment issues. Nevertheless, there are exceptions to every rule, and your mileage may vary.

I’ll take web sites for $200, Alex: Part I

I’m one of those throwbacks that learned HTML by typing it in Notepad. I’ve since moved up to using the Visual Studio editor; it does syntax coloring, error highlighting, and has a “design” mode for previewing the page, yet it’s a very utilitarian editor that I feel comfortable with. I do use FrontPage when I need to manage connections between multiple HTML pages, but mostly in raw HTML mode. When I use WYSIWYG design mode in FrontPage, I inevitably end up cleaning out a lot of unnecessary junk that it includes in the generated HTML. I think it’s fair to say that my obsession with clean HTML results in utilitarian, functional, and standards conformant presentations — but with a decided lack of graphic appeal.

The ManuSoft and CADLock web sites are examples of this utilitarian approach. The ManuSoft site uses no fancy graphics and relies very little on client side scripting, and it supports a hierarchical navigation system using only standard hyperlinks. I like that minimalist approach, but the price for clean HTML being served to clients is a lot of work on the server to maintain the site. As a result, I don’t update the site very often because it’s just too difficult.

This blog was the first step toward realizing a goal of making it easier to add new content. After all, the raison d’être of blogs is to minimize the latency between the writer’s stream of consciousness and words on the web by making it irresistibly easy to add new content. This is precisely why blogs have become so popular.

Unfortunately, I soon found limitations with my blog. Tabular lists of data still require manual HTML input, it is difficult to customize the content area outside the individual posts on the blog page, and most aspects of the hosted blog software are outside my control. I wanted more.

The Autodesk vs. Open Design Alliance lawsuit gave me an excuse to take the next step: implement the “blog” concept across an entire web site with software that I control. So, I decided to swallow my pride and learn how to create an entire web site that would be so easy to update that I would actually update it frequently — even if it meant messy HTML code. Stay tuned for Part II, choosing a hosting service and deciding which software to use.