Nobody could have failed to notice the recent resurgence of interest in the C++ programming language. In particular, the recent Build conference was the most we’ve seen Microsoft talking about C++ for several years. Why has a language that’s been languishing in the “prehistoric irrelevance” category for so long suddenly come back into vogue?
Continue reading C++: The oldest new kid on the block
Tag Archives: win32
Where’s my window?
On Windows, if you regularly change screen resolution or size, perhaps by accessing a machine remotely, you might find some of your application windows are no longer visible; they’re positioned outside of the visible display area. If you can’t see the window, it can be a little difficult to use the application. How can you get that window back?
Continue reading Where’s my window?
Beware of using stack-based COM objects from .NET
There are all sorts of nasty things to be aware of if you’re mixing reference-counted COM objects with garbage-collected .NET. For instance, if you’re implementing COM objects in C++ then you’re free to allocate them anywhere you like; on the heap or perhaps on the stack if you know they’re only used in some specific scope.
But what happens if during the lifetime of that stack based COM object, it gets used from .NET? A runtime callable wrapper (RCW) will be created around the object. And this RCW expects to be able to keep the underlying object alive by incrementing its reference count. Of course, the stack-based object will soon go out of scope, and regardless of its reference count the object will be destroyed and the pointer that the RCW contains will no longer be valid. It points into the stack, so when the RCW gets cleaned-up, the CLR will call via this pointer into memory that contains garbage and you’ll get something nasty like an access violation or illegal instruction exception.
Continue reading Beware of using stack-based COM objects from .NET
Don’t do anything in DllMain… Please
Novice Windows programmers can often think that DllMain is a good place to get that one-time set-up and tear-down work done. It seems to offer an ideal opportunity to know when your DLL has just been loaded, and when it’s about to be unloaded. What better place to add all that expensive, complicated initialisation…? STOP! WAIT! Before you add anything in DllMain, make sure you understand what state the process will be in when it gets called. Once you know that, you may well change your mind…
Continue reading Don’t do anything in DllMain… Please
The 7 signs your UI was created by a programmer
Do you suspect a programmer may have put together the terrible user interface on that “enterprise” software you’re forced to use every day? There are some give-away indicators. Look out for them in your software, hunt down the developer and force them to read a book about user interface design
1. Exclamation marks in dialog box messages
Look, it’s probably the 50th time I’ve seen this message today. The fact that this application “Cannot connect to database!” is no longer a surprise. You may have noticed that most professional software uses a neutral tone for its communication with the user. Try that. Also:
1a. Double negatives in confirmation dialogs
“Are you sure you don’t want to lose your changes?” Err… what? No. I mean YES. Oh sh*t. Any dialog that requires you to stop and try to parse the question in order to work out if you’re about to destroy several hours of work is not doing its job. It’s getting in the way of you doing your job. In fact, convoluted messages are such a serious issue that Microsoft even tried to help developers to help their users by introducing a whole new kind of dialog box in Vista: the question/task dialog. Good luck with that.
2. No tab ordering defined\mouse only navigation
Because no-one’s ever going to use the keyboard to navigate the zillion controls in your data entry app, are they? This one actually surprises me, because I’d have thought that developers would’ve needed to navigate quickly through the application while they’re writing it. Well, that doesn’t seem to be the case. Pretty much all commercial apps are good counter examples. I don’t mean to hold up Microsoft Office as a paragon of UI virtue, but they definitely do the “alternate way of navigating everything” thing well. Everything you need can be reached by both keyboard and mouse. Unplug your mouse and try that with your favourite piece of in-house software and see how you get on.
3. Group boxes around everything
This is a bit of a WinForms specific one. The clue is in the name: group boxes are for grouping logically related controls, not for providing a kewl recessed border around every single one of the controls in your dialog. Don’t kid yourself that this is doing anything other than using up some valuable screen real estate. (See if you can spot another pet peeve in the example dialog, too).
4. Icons created in the IDE
Look, Visual Studio’s a really good integrated development environment, but it ain’t no Photoshop. Don’t try and use it to create icons. And while you’re at it, please don’t make icons consisting solely of the name of your application (inevitably an acronym) in pixel font and primary colours. Oh, and don’t just steal various icons from another application, unless you’re going to steal the whole lot; one of the key visual aspects of a good UI is consistency. Mixing your hand-drawn 4-bit icons with the glorious 32-bit shiny ones you borrowed is going to be jarring. In fact, why not go the whole way and get someone who can actually draw to create your icons for you? After all, you wouldn’t have someone who wasn’t a programmer writing the code, would you…?
5. Data grids
Otherwise known as the “Excel is the pinnacle of user interface design” disease. Break the habit. Generally, the more types of controls that are embedded in your grid, the less likely that it’s the right kind of interface paradigm. Yeah, I’m looking at you, person embedding a calendar control, drop down box, graph, slider and checkbox in each row of a data grid. And whatever your 3rd-party grid provider of choice says, it’s not going to do screen redraw performance any good, either.
6. Not implemented message boxes
Ahh, the GUI equivalent of source code TODO comments. Of course, it’s an in-house software give-away; no commercial (desktop) software would be brazen enough to ship with bits of functionality dangling from the stumps of buttons and menu items. Would it? Feel free to provide counter-examples if you have them.
7. Excessive use of dialog boxes
Warning: dialog boxes are considered harmful (to usability). They’re the equivalent of restraining your user by force and preventing her from moving until she answers your question. That might be OK for matters of life or death (i.e. data loss), but not otherwise. Every time you find yourself about to add a new message box, stop, take a deep breath and consider whether it’s really necessary.
So, if you’re a victim or one, many, or all of these user interface faux pas, all I can say is: sorry. I’ve been responsible for doing at least one of these things myself over the years. Consider this post repentance for my user interface sins.
Finding the largest free block of address space
I’ve been seeing problems recently with fragmented virtual address space. During the lifetime of a process, bits and pieces of memory are allocated throughout the 2GB 32-bit address space to such an extent that large contiguous blocks of free space are no longer available. If anything subsequently requires a large block of memory (like, for instance, a somewhat out-of-date version of the GHC runtime), it will fail to get it.
It’s obvious looking at the output from VMmap or windbg’s !address command what the largest contiguous block is, e.g.
0:008> !address -summary .... Largest free region: Base 07300000 - Size 63ed0000 (1637184 KB)
But what if you need that number in order to make a decision at run-time? For instance, to decide whether your process is in a fit state to continue, or if it should instead commit hara-kiri. In that case, you need to access the information programmatically. That’s where the immensely useful VirtualQueryEx function comes in…
Continue reading Finding the largest free block of address space
Diagnosing out of memory errors with VMMap
The other day a colleague pointed me to a new tool from Mark Russinovich et al (ex-SysInternals) that turns out to be very useful for diagnosing virtual memory/address space exhaustion issues. I thought I’d describe it here, and give some – hopefully useful – extra information on what it reports.
(I had problems with WordPress choking on this long post, so I’ve split it into 2 parts. This the first part, the second part is here).
Programmatically checking memory usage
One of the things that’s useful in a pre-release check is do a regression test on the memory usage of your unmanaged functions. This should help to ensure that the fantastic new data structure you introduced doesn’t cost too much in additional storage for the order-of-magnitude performance improvement you were boasting about.
Like most of my posts, this assumes that it’s not feasible to go through all your source code, and say, replace all instances of new with a version that tracks usage (the approach used by the debug CRT). As well as being logistically infeasible, this also tends to miss allocations that don’t go via new, for example, direct calls to HeapAlloc.