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  • Throwing a C++ exception from inside a Linux Signal handler

    - by SoapBox
    As a thought experiment more than anything I am trying to get a C++ exception thrown "from" a linux signal handler for SIGSEGV. (I'm aware this is not a solution to any real world SIGSEGV and should never actually be done, but I thought I would try it out after being asked about it, and now I can't get it out of my head until I figure out how to do it.) Below is the closest I have come, but instead of the signal being caught properly, terminate() is being called as if no try/catch block is available. Anyone know why? Or know a way I can actually get a C++ exception from a signal handler? The code (beware, the self modifying asm limits this to running on x86_64 if you're trying to test it): #include <iostream> #include <stdexcept> #include <signal.h> #include <stdint.h> #include <errno.h> #include <string.h> #include <sys/mman.h> using namespace std; uint64_t oldaddr = 0; void thrower() { cout << "Inside thrower" << endl; throw std::runtime_error("SIGSEGV"); } void segv_handler(int sig, siginfo_t *info, void *pctx) { ucontext_t *context = (ucontext_t *)pctx; cout << "Inside SIGSEGV handler" << endl; oldaddr = context->uc_mcontext.gregs[REG_RIP]; uint32_t pageSize = (uint32_t)sysconf(_SC_PAGESIZE); uint64_t bottomOfOldPage = (oldaddr/pageSize) * pageSize; mprotect((void*)bottomOfOldPage, pageSize*2, PROT_READ|PROT_WRITE|PROT_EXEC); // 48 B8 xx xx xx xx xx xx xx xx = mov rax, xxxx *((uint8_t*)(oldaddr+0)) = 0x48; *((uint8_t*)(oldaddr+1)) = 0xB8; *((int64_t*)(oldaddr+2)) = (int64_t)thrower; // FF E0 = jmp rax *((uint8_t*)(oldaddr+10)) = 0xFF; *((uint8_t*)(oldaddr+11)) = 0xE0; } void func() { try { *(uint32_t*)0x1234 = 123456789; } catch (...) { cout << "caught inside func" << endl; throw; } } int main() { cout << "Top of main" << endl; struct sigaction action, old_action; action.sa_sigaction = segv_handler; sigemptyset(&action.sa_mask); action.sa_flags = SA_SIGINFO | SA_RESTART | SA_NODEFER; if (sigaction(SIGSEGV, &action, &old_action)<0) cerr << "Error setting handler : " << strerror(errno) << endl; try { func(); } catch (std::exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The actual output: Top of main Inside SIGSEGV handler Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): SIGSEGV Aborted Expected output: Top of main Inside thrower caught inside func Caught : SIGSEGV Bottom of main

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  • Throwing a C++ exception after an inline-asm jump

    - by SoapBox
    I have some odd self modifying code, but at the root of it is a pretty simple problem: I want to be able to execute a jmp (or a call) and then from that arbitrary point throw an exception and have it caught by the try/catch block that contained the jmp/call. But when I do this (in gcc 4.4.1 x86_64) the exception results in a terminate() as it would if the exception was thrown from outside of a try/catch. I don't really see how this is different than throwing an exception from inside of some far-flung library, yet it obviously is because it just doesn't work. How can I execute a jmp or call but still throw an exception back to the original try/catch? Why doesn't this try/catch continue to handle these exceptions as it would if the function was called normally? The code: #include <iostream> #include <stdexcept> using namespace std; void thrower() { cout << "Inside thrower" << endl; throw runtime_error("some exception"); } int main() { cout << "Top of main" << endl; try { asm volatile ( "jmp *%0" // same thing happens with a call instead of a jmp : : "r"((long)thrower) : ); } catch (exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The expected output: Top of main Inside thrower Caught : some exception Bottom of main The actual output: Top of main Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): some exception Aborted

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  • std::basic_string full specialization (g++ conflict)

    - by SoapBox
    I am trying to define a full specialization of std::basic_string< char, char_traits<char>, allocator<char> > which is typedef'd (in g++) by the <string> header. The problem is, if I include <string> first, g++ sees the typedef as an instantiation of basic_string and gives me errors. If I do my specialization first then I have no issues. I should be able to define my specialization after <string> is included. What do I have to do to be able to do that? My Code: #include <bits/localefwd.h> //#include <string> // <- uncommenting this line causes compilation to fail namespace std { template<> class basic_string< char, char_traits<char>, allocator<char> > { public: int blah() { return 42; } size_t size() { return 0; } const char *c_str() { return ""; } void reserve(int) {} void clear() {} }; } #include <string> #include <iostream> int main() { std::cout << std::string().blah() << std::endl; } The above code works fine. But, if I uncomment the first #include <string> line, I get the following compiler errors: blah.cpp:7: error: specialization of ‘std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ after instantiation blah.cpp:7: error: redefinition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ /usr/include/c++/4.4/bits/stringfwd.h:52: error: previous definition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ blah.cpp: In function ‘int main()’: blah.cpp:22: error: ‘class std::string’ has no member named ‘blah’ Line 52 of /usr/include/c++/4.4/bits/stringfwd.h: template<typename _CharT, typename _Traits = char_traits<_CharT>, typename _Alloc = allocator<_CharT> > class basic_string; As far as I know this is just a forward delcaration of the template, NOT an instantiation as g++ claims. Line 56 of /usr/include/c++/4.4/bits/stringfwd.h: typedef basic_string<char> string; As far as I know this is just a typedef, NOT an instantiation either. So why are these lines conflicting with my code? What can I do to fix this other than ensuring that my code is always included before <string>?

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  • Watch YouTube in Windows 7 Media Center

    - by Mysticgeek
    Have you been looking for a way to watch your favorite viral videos from YouTube and Dailymotion from the couch? Today we take a look at an easy to use plugin which allows you to watch streaming video in Windows 7 Media Center. Install Macrotube The first thing we need to do is download and install the plugin called Macrotube (link below) following the defaults through the install wizard. After it’s installed, open Windows 7 Media Center and you’ll find Macrotube in the main menu. Currently there are three services available…YouTube, Dailymotion, and MSN Soapbox. Just select the service where you want to check out some videos. You can browse through different subjects or categories… Or you can search the the service by typing in what you’re looking for…with your remote or keyboard. There is the ability to drill down you search content by date, rating, views, and relevance. There are a few settings available such as the language beta, auto updates, and appearance. Now just kick back and browse through the different services and watch what you want from the comfort of your couch or on your computer. Conclusion This neat project is still in development and the developer is continuing to add changes through updates. It only works with Windows 7 Media Player, but there is a 32 & 64-bit version. Sometimes we experiences certain videos that wouldn’t play and it did crash a few times, but that is to be expected with a work in progress. But overall, this is a cool plugin that will allow you to watch your favorite online content from WMC. Download Macrotube and get more details and troubleshooting help fro the GreenButton forum Similar Articles Productive Geek Tips Using Netflix Watchnow in Windows Vista Media Center (Gmedia)Integrate Hulu Desktop and Windows Media Center in Windows 7Automatically Start Windows 7 Media Center in Live TV ModeWatch TV Programming Without a TV Tuner In Window 7 Media CenterAutomatically Mount and View ISO files in Windows 7 Media Center TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 NachoFoto Searches Images in Real-time Office 2010 Product Guides Google Maps Place marks – Pizza, Guns or Strip Clubs Monitor Applications With Kiwi LocPDF is a Visual PDF Search Tool Download Free iPad Wallpapers at iPad Decor

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  • Can you Trust Search?

    - by David Dorf
    An awful lot of referrals to e-commerce sites come from web searches. Retailers rely on search engine optimization (SEO) to correctly position their website so they can be found. Search on "blue jeans" and the results are determined by a semi-secret algorithm -- in my case Levi.com, Banana Republic, and ShopStyle show up. The NY Times recently uncovered a situation where JCPenney, via third-parties hired to help with SEO, was caught manipulating search results so they were erroneously higher in page rankings. No doubt this helped drive additional sales during this part Christmas. The article, The Dirty Little Secrets of Search, is well worth reading. My friend Ron Kleinman started an interesting discussion at the ARTS Linkedin forum. He posed the question: The ability of a single company to "punish" any retailer (by significantly impacting their on-line sales volume) who does not play by their rules ... is this a good thing or a bad thing? Clearly JCP was in the wrong and needed to be punished, but should that decision lie with Google alone? Don't get me wrong -- I'm certainly not advocating we create a Department of Search where bureaucrats think of ways to spend money, but Google wields an awful lot of power in this situation, and it makes me feel uncomfortable. Now Google is incorporating more social aspects into their search results. For example, when Google knows its me (i.e. I'm logged in when using Google) search results will be influenced by my Twitter network. In an effort to increase relevance, the blogs and re-tweeted articles from my network will be higher in the search results than they otherwise would be. So in the case of product searches, things discussed in my network will rise to the top. Continuing my blue jean example, if someone in my network had been discussing Macy's perhaps they would now be higher in the result set. soapbox: I already have lots of spammers posting bogus comments to this blog in an effort to create additional links to their sites and thus increase their search ranking. Should I expect a similar situation in Twitter and eventually Facebook? Now retailers need to expand their SEO efforts to incorporate social media as well, but do us all a favor and please don't cheat.

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  • XNA Notes 004

    - by George Clingerman
    The XNA community has been crazy busy again. It always make me fee like such a slacker collecting all of these notes as I see the tremendous output from people all over the world and it’s incredible and humbling. There are some amazingly skilled people working with XNA. On another not, I’m going to take a minute to get on my soapbox and say, if you are developing ANYTHING and are not using some sort of source/revision control, START IMMEDIATELY. This applies to teams of one. Projects for fun. And “I back up my hard drive” or “I use dropbox!” does NOT count as using source control. You’ll be doing yourself a HUGE favor if you find one, learn to use it and integrate it into your everyday workflow. I personally use Subversion. It’s hosted offsite at xp.dev.com and I use TortoiseSVN as my front end to interface with the repository. It’s simple and easy to use and has saved me from myself so many time. Honestly, get setup with some type of source control immediately. If you don’t understand how, grab another developer that does and have them walk you through setup and the basics of using it. Ok, I’m done. On to the notes… The XNA Team Only 14 days left to Submit XNA GS 3.1 Games! http://blogs.msdn.com/b/xna/archive/2011/01/24/14-days-left-to-submit-xna-gs-3-1-games-on-app-hub.aspx Shawn Hargreaves shares some great information on Exception Handling best practices on the XNA forums http://forums.create.msdn.com/forums/p/73333/448556.aspx#448556 http://blogs.msdn.com/b/ericlippert/archive/2008/09/10/vexing-exceptions.aspx XNA MVPs @CatalinZima gives us a peek at Chicken’s Can’t Fly http://www.amusedsloth.com/games/chickens-cant-fly/ Screen-space deformations in XNA for WP7 from Catalin Zima http://twitter.com/CatalinZima/statuses/30313083767357440 http://www.amusedsloth.com/2011/01/screen-space-deformations-in-xna-for-windows-phone-7/ XNA Developers Going to GDC? Don’t miss the XNA panel hosted by a plethora of well known XNA community names! http://forums.create.msdn.com/forums/p/73576/448842.aspx#448842 MasterBlud does an interview with @Xalterax http://twitter.com/MasterBlud/statuses/28510774812999680 http://www.xboxhornet.com/wordpress/?p=7102 Luke Schneider of Radiangames posts about The Radiangames Style http://radiangames.com/?p=532 Holmade Games had a “vote for the new playable character” poll going on for Hurdle Turtle this past week http://holmadegames.blogspot.com/2011/01/new-level-pack-vote-for-your-favorite.html IGF v0.1.0.0 release post mortem http://indiefreaks.com/2011/01/24/v0-1-0-0-release-post-mortem/ James an Super Dunner post Good Morning Gato #46 and a look at the Vampire Smile box art http://www.ska-studios.com/2011/01/21/good-morning-gato-46/ http://www.ska-studios.com/2011/01/20/vampire-smiles-digital-box-art/ Alfredo Di Napoli creates Cow Pong using XNA and F#! http://alfredodinapoli.wordpress.com/2011/01/25/cow-pong-a-simple-xna-game-in-f/ Xbox LIVE Indie Games Signed In Podcast posts Episode #61 http://www.signedinpodcast.com/?p=559 Gamergeddon posts the January 23rd edition of XBLIG Round Up http://www.gamergeddon.com/2011/01/23/xbox-indie-games-round-up-january-23rd/ Indie Asylum posts Antipole Review http://www.indieasylum.com/reviews/38-xblig/112-antipole.html 1UPOrPosion Reviews OSR Unhinged http://www.1uporpoison.com/xblig/osr-unhinged/ DarkstarMatryx review Warbirds at Work http://www.darkstarmatryx.com/?p=185 Review of Aban Hawkins and the 1000 Spikes http://www.armlessoctopus.com/2011/01/24/xbox-indie-review-aban-hawkins-the-1000-spikes/ XboxHornet reviews Corrupted http://www.xboxhornet.com/wordpress/?p=7123 XBLIG 2010: The Best And The Worst http://www.gamasutra.com/blogs/JamieMann/20110121/6840/ Xbox LIVE Arcade Sales Analysis - an interesting read for XBLIG developers wondering how they’re doing compared to arcade.. http://www.gamerbytes.com/2011/01/xbla_sales_analysis_dec_2010.php Best of Indies for January 25th http://www.thisisfakediy.co.uk/articles/games/best-of-the-indies-25th-january-2011 Decimation X3 appears as an arcade machine in the wild! http://twitter.com/mdoucette/statuses/29605562484260864 XNA Game Development Guiseppe De Francesco (@PinoEire) announced Torque X 4.0 CEV is now in RC phase! http://www.garagegames.com/community/blogs/view/20779 DrMistry of mstargames shares his struggle (and mistakes) with learning to use the Content Pipeline http://www.mstargames.co.uk/mistryblogmain/35-genblog/181-pontent-cipeline-more-like-it.html New Tutorial posted XNA 2D Basic Collision Detection with Rotation from Ioannis Panagopoulos http://www.progware.org/Blog/post/XNA-2D-Basic-Collision-Detection-with-Rotation.aspx Sgt. Conker roars to life! Doing a much better (and prettier) job of collecting XNA news from around the interwebs. http://www.sgtconker.com/ http://www.sgtconker.com/2011/01/dedication-for-captain-boki/ http://www.sgtconker.com/2011/01/screen-space-deformations-in-xna-for-windows-phone-7/ http://www.sgtconker.com/2011/01/xna-4-0-light-pre-pass-2/ http://www.sgtconker.com/2011/01/indiefreaks-game-framework-0-1-0-0-released/ Offering a little free publicity for XBLIGs http://forums.create.msdn.com/forums/p/73465/448321.aspx#448321 Ben Kane writes about building loot tables from Excel using the Content Pipeline http://benkane.wordpress.com/2011/01/23/building-loot-tables-from-excel-using-the-content-pipeline/ Good tips on attracting a game artist AND an offer to create your cover art for FREE http://forums.create.msdn.com/forums/t/72998.aspx If you’re an XBLIG developer keeping your eye on places to release on the PC, might want to be watching the IndieCity blog. Seems like these guys are well on their way to constructing something worth watching. http://www.indiecity.com/blog/ DVMGames spotted a new crowd-funding site for Indies http://twitter.com/DVMGames/statuses/29947274767372289 http://www.8bitfunding.com/ Transmute continues to make progress and there’s a nice dev blog to follow along here http://forgottenstarstudios.com/blog/

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  • Soft lockup after upgrade - cannot install from live CD

    - by nbm
    I dual-boot MacIntel Core 2 duo. nVidia graphics. Ran upgrade from ubuntu 13.10 to 14.04 (64 bit). On restart ran into {numbers} Bug: soft lockup - CPU#0 stuck for 22s! [swapper/0:1] Tried loading earlier kernel: same problem Tried re-installing ubuntu from a liveCD that has worked in the past: version 13.04. Same problem. Tried re-partitioning hard drive using Mac OS X disk utility and then installing ubuntu 14.04LTS from liveCD. Same problem. Not possible to verify liveCD disk (creates same "soft lockup" bug.) Tried installing from the liveCD with version 13.04 that I know works (that's how I got Ubuntu on this machine in the first place.) Same problem. I know this is not a hardware problem as OS X works just fine, I am using it right now on the same machine. I have been using various versions of Ubuntu for 2 years. Things I cannot do: Open a terminal Verify CD image Start ubuntu from CD (same soft lockup problem) This problem is similar to some other questions, none of which have been satisfactorily answered: Ubuntu 14.04 soft lockup on Vostro 3500 Cannot do fresh install of Ubuntu 13.04 while booting from DVD: "soft lockup" bug Live CD stalls when installing Ubuntu 13.10 UPDATE 6/11/14: Following some much-appreciated advice from bain (see below) I burned a 12.04LTS disk and started with kernel parameters: noapic, no1apic, acpi=off, nomodeset, elevator=deadline, and clocksource=jiffies. With all of these parameters I was able to load the 12.04LTS CD ("Try without installing"). It worked fine. However, as soon as I tried to install Ubuntu from the CD, my wired ethernet (eth0) connection would hang. There are already various askubuntu questions and bug reports about this problem, none of which had answers for me. (E.g., dhclient eth0 does nothing, none of the various reset commands does anything, manually setting IP &etc does nothing. I could reliably kill the ethernet connection by clicking "install ubuntu" every single time.) I could go ahead and install 12.04 without an internet connection, but the install would freeze after mostly completing (I tried several times.) There were some relevant error messages in the details of the install output script that, IIRC, had to do with searching for missing files and not being able to access eth0 (internet) to get them. To be honest I gave up at that point and I'm not sure I wrote those down. If I find some notes I will post them. At this point I no longer have Ubuntu on my system. I wiped the partitions and am using exclusively OS X. I am leaving this question in case it helps anyone else with similar problems. I love open source and I love Linux, and the next machine I get I will probably just build from Arch. At the moment I miss repositories and a lot of other things about Ubuntu, but the OS X terminal is 'nix, I can pretty much use all the open source apps I like, and while I am not a fan of the Apple software it gets the job done for me. Unlike Ubuntu, which can't even install. I realize this isn't necessarily a place for a soapbox speech, but when I first installed 12.04 several years ago there were already people in the community complaining that Canonical was going too "commercial". But I loved it. Several years later and all I've seen is Canonical adding more not-so-useful bells and whistles to Ubuntu while continually failing to fix basic problems on upgrades. With a dual-boot (and sometimes triple-boot) system it always took me some tweaking to get an upgrade to work, and to some extent that is okay. But at this point I feel like Canonical ought to just put a price tag on Ubuntu. All I see is more commercialism and advertising and product tie-ins, and ongoing problems do not get fixed. I am a big fan of open-source, not-for profit enterprise. I am also a big fan of for-profit enterprise, which certainly has its place and usefulness. I am not a fan of companies who pretend to be in favor of open source but really are just out to make a buck, and IMNSHO that is what Canonical has become. This is a great community and I wish you all the best, but my next install of Linux will not be Ubuntu.

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  • Why unhandled exceptions are useful

    - by Simon Cooper
    It’s the bane of most programmers’ lives – an unhandled exception causes your application or webapp to crash, an ugly dialog gets displayed to the user, and they come complaining to you. Then, somehow, you need to figure out what went wrong. Hopefully, you’ve got a log file, or some other way of reporting unhandled exceptions (obligatory employer plug: SmartAssembly reports an application’s unhandled exceptions straight to you, along with the entire state of the stack and variables at that point). If not, you have to try and replicate it yourself, or do some psychic debugging to try and figure out what’s wrong. However, it’s good that the program crashed. Or, more precisely, it is correct behaviour. An unhandled exception in your application means that, somewhere in your code, there is an assumption that you made that is actually invalid. Coding assumptions Let me explain a bit more. Every method, every line of code you write, depends on implicit assumptions that you have made. Take this following simple method, that copies a collection to an array and includes an item if it isn’t in the collection already, using a supplied IEqualityComparer: public static T[] ToArrayWithItem( ICollection<T> coll, T obj, IEqualityComparer<T> comparer) { // check if the object is in collection already // using the supplied comparer foreach (var item in coll) { if (comparer.Equals(item, obj)) { // it's in the collection already // simply copy the collection to an array // and return it T[] array = new T[coll.Count]; coll.CopyTo(array, 0); return array; } } // not in the collection // copy coll to an array, and add obj to it // then return it T[] array = new T[coll.Count+1]; coll.CopyTo(array, 0); array[array.Length-1] = obj; return array; } What’s all the assumptions made by this fairly simple bit of code? coll is never null comparer is never null coll.CopyTo(array, 0) will copy all the items in the collection into the array, in the order defined for the collection, starting at the first item in the array. The enumerator for coll returns all the items in the collection, in the order defined for the collection comparer.Equals returns true if the items are equal (for whatever definition of ‘equal’ the comparer uses), false otherwise comparer.Equals, coll.CopyTo, and the coll enumerator will never throw an exception or hang for any possible input and any possible values of T coll will have less than 4 billion items in it (this is a built-in limit of the CLR) array won’t be more than 2GB, both on 32 and 64-bit systems, for any possible values of T (again, a limit of the CLR) There are no threads that will modify coll while this method is running and, more esoterically: The C# compiler will compile this code to IL according to the C# specification The CLR and JIT compiler will produce machine code to execute the IL on the user’s computer The computer will execute the machine code correctly That’s a lot of assumptions. Now, it could be that all these assumptions are valid for the situations this method is called. But if this does crash out with an exception, or crash later on, then that shows one of the assumptions has been invalidated somehow. An unhandled exception shows that your code is running in a situation which you did not anticipate, and there is something about how your code runs that you do not understand. Debugging the problem is the process of learning more about the new situation and how your code interacts with it. When you understand the problem, the solution is (usually) obvious. The solution may be a one-line fix, the rewrite of a method or class, or a large-scale refactoring of the codebase, but whatever it is, the fix for the crash will incorporate the new information you’ve gained about your own code, along with the modified assumptions. When code is running with an assumption or invariant it depended on broken, then the result is ‘undefined behaviour’. Anything can happen, up to and including formatting the entire disk or making the user’s computer sentient and start doing a good impression of Skynet. You might think that those can’t happen, but at Halting problem levels of generality, as soon as an assumption the code depended on is broken, the program can do anything. That is why it’s important to fail-fast and stop the program as soon as an invariant is broken, to minimise the damage that is done. What does this mean in practice? To start with, document and check your assumptions. As with most things, there is a level of judgement required. How you check and document your assumptions depends on how the code is used (that’s some more assumptions you’ve made), how likely it is a method will be passed invalid arguments or called in an invalid state, how likely it is the assumptions will be broken, how expensive it is to check the assumptions, and how bad things are likely to get if the assumptions are broken. Now, some assumptions you can assume unless proven otherwise. You can safely assume the C# compiler, CLR, and computer all run the method correctly, unless you have evidence of a compiler, CLR or processor bug. You can also assume that interface implementations work the way you expect them to; implementing an interface is more than simply declaring methods with certain signatures in your type. The behaviour of those methods, and how they work, is part of the interface contract as well. For example, for members of a public API, it is very important to document your assumptions and check your state before running the bulk of the method, throwing ArgumentException, ArgumentNullException, InvalidOperationException, or another exception type as appropriate if the input or state is wrong. For internal and private methods, it is less important. If a private method expects collection items in a certain order, then you don’t necessarily need to explicitly check it in code, but you can add comments or documentation specifying what state you expect the collection to be in at a certain point. That way, anyone debugging your code can immediately see what’s wrong if this does ever become an issue. You can also use DEBUG preprocessor blocks and Debug.Assert to document and check your assumptions without incurring a performance hit in release builds. On my coding soapbox… A few pet peeves of mine around assumptions. Firstly, catch-all try blocks: try { ... } catch { } A catch-all hides exceptions generated by broken assumptions, and lets the program carry on in an unknown state. Later, an exception is likely to be generated due to further broken assumptions due to the unknown state, causing difficulties when debugging as the catch-all has hidden the original problem. It’s much better to let the program crash straight away, so you know where the problem is. You should only use a catch-all if you are sure that any exception generated in the try block is safe to ignore. That’s a pretty big ask! Secondly, using as when you should be casting. Doing this: (obj as IFoo).Method(); or this: IFoo foo = obj as IFoo; ... foo.Method(); when you should be doing this: ((IFoo)obj).Method(); or this: IFoo foo = (IFoo)obj; ... foo.Method(); There’s an assumption here that obj will always implement IFoo. If it doesn’t, then by using as instead of a cast you’ve turned an obvious InvalidCastException at the point of the cast that will probably tell you what type obj actually is, into a non-obvious NullReferenceException at some later point that gives you no information at all. If you believe obj is always an IFoo, then say so in code! Let it fail-fast if not, then it’s far easier to figure out what’s wrong. Thirdly, document your assumptions. If an algorithm depends on a non-trivial relationship between several objects or variables, then say so. A single-line comment will do. Don’t leave it up to whoever’s debugging your code after you to figure it out. Conclusion It’s better to crash out and fail-fast when an assumption is broken. If it doesn’t, then there’s likely to be further crashes along the way that hide the original problem. Or, even worse, your program will be running in an undefined state, where anything can happen. Unhandled exceptions aren’t good per-se, but they give you some very useful information about your code that you didn’t know before. And that can only be a good thing.

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