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  • What version control system is best designed to *prevent* concurrent editing?

    - by Fred Hamilton
    We've been using CVS (with TortoiseCVS interface) for years for both source control and wide-ranging document control (including binaries such as Word, Excel, Framemaker, test data, simulation results, etc.). Unlike typical version control systems, 99% of the time we want to prevent concurrent editing - when a user starts editing a file, the pre-edit version of the file becomes read only to everyone else. Many of the people who will be using this are not programmers or even that computer savvy, so we're also looking for a system that let's people simply add documents to the repository, check out and edit a document (unless someone else is currently editing it), and check it back in with a minimum of fuss. We've gotten this to work reasonably well with CVS + TortoiseCVS, but we're now considering Subversion and Mercurial (and open to others if they're a better fit) for their better version tracking, so I was wondering which one supported locking files most transparently. For example, we'd like exclusive locking enabled as the default, and we want to make it as difficult as possible for someone to accidentally start editing a file that someone else has checked out. For example when someone checks out a file for editing, it checks with the master database first even if they have not recently updated their sandbox. Maybe it even won't let a user check out a document if it's off the network and can't check in with the mothership.

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  • Write Scheme data structures so they can be eval-d back in, or alternative

    - by Jesse Millikan
    I'm writing an application (A juggling pattern animator) in PLT Scheme that accepts Scheme expressions as values for some fields. I'm attempting to write a small text editor that will let me "explode" expressions into expressions that can still be eval'd but contain the data as literals for manual tweaking. For example, (4hss->sexp "747") is a function call that generates a legitimate pattern. If I eval and print that, it becomes (((7 3) - - -) (- - (4 2) -) (- (7 2) - -) (- - - (7 1)) ((4 0) - - -) (- - (7 0) -) (- (7 2) - -) (- - - (4 3)) ((7 3) - - -) (- - (7 0) -) (- (4 1) - -) (- - - (7 1))) which can be "read" as a string, but will not "eval" the same as the function. For this statement, of course, what I need would be as simple as (quote (((7 3... but other examples are non-trivial. This one, for example, contains structs which print as vectors: pair-of-jugglers ; --> (#(struct:hand #(struct:position -0.35 2.0 1.0) #(struct:position -0.6 2.05 1.1) 1.832595714594046) #(struct:hand #(struct:position 0.35 2.0 1.0) #(struct:position 0.6 2.0500000000000003 1.1) 1.308996938995747) #(struct:hand #(struct:position 0.35 -2.0 1.0) #(struct:position 0.6 -2.05 1.1) -1.3089969389957472) #(struct:hand #(struct:position -0.35 -2.0 1.0) #(struct:position -0.6 -2.05 1.1) -1.8325957145940461)) I've thought of at least three possible solutions, none of which I like very much. Solution A is to write a recursive eval-able output function myself for a reasonably large subset of the values that I might be using. There (probably...) won't be any circular references by the nature of the data structures used, so that wouldn't be such a long job. The output would end up looking like `(((3 0) (... ; ex 1 `(,(make-hand (make-position ... ; ex 2 Or even worse if I could't figure out how to do it properly with quasiquoting. Solution B would be to write out everything as (read (open-input-string "(big-long-s-expression)")) which, technically, solves the problem I'm bringing up but is... ugly. Solution C might be a different approach of giving up eval and using only read for parsing input, or an uglier approach where the s-expression is used as directly data if eval fails, but those both seem unpleasant compared to using scheme values directly. Undiscovered Solution D would be a PLT Scheme option, function or library I haven't located that would match Solution A. Help me out before I start having bad recursion dreams again.

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  • Dynamic allocating of const member structures

    - by Willy
    I've got class which is using plain-only-data struct with const variables and I'm not sure, if I'm allocating these structures in a proper way. It looks more or less like: #include <cstdlib> #include <iostream> using std::cout; using std::endl; struct some_const_struct { const int arg1; const int arg2; }; class which_is_using_above_struct { public: some_const_struct* m_member; const some_const_struct* const m_const_member; public: const some_const_struct& get_member() const { return *m_member; } const some_const_struct& get_const_member() const { return *m_const_member; } void set_member(const int a, const int b) { if(m_member != NULL) { delete m_member; m_member = NULL; } m_member = new some_const_struct((some_const_struct){a, b}); } explicit which_is_using_above_struct(const int a, const int b) : m_const_member(new some_const_struct((const some_const_struct){a, b})) { m_member = NULL; } ~which_is_using_above_struct() { if(m_member != NULL) { delete m_member; } if(m_const_member != NULL) { delete m_const_member; } } }; int main() { which_is_using_above_struct c(1, 2); c.set_member(3, 4); cout << "m_member.arg1 = " << c.get_member().arg1 << endl; cout << "m_member.arg2 = " << c.get_member().arg2 << endl; cout << "m_const_member.arg1 = " << c.get_const_member().arg1 << endl; cout << "m_const_member.arg2 = " << c.get_const_member().arg2 << endl; return 0; } I'm just not quite sure if the statement: m_member = new some_const_struct((some_const_struct){a, b}); doesn't produce unnessesary use of some_const_struct's copy constructor, ergo allocating that struct twice. What do you think? And is it reasonable to make that struct's members const? (they're not supposed to change in their lifetime at all)

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  • How does a web server/the http protocol handle version control and compression?

    - by Sune Rasmussen
    When a client browser requests a file from the web server, I know that some kind of check is performed, because the files needed to serve the web page may already be cached by the web browser. So, if a file exists in the cache, no files are sent. But if the file on the server has changed since the file was cached in the browser, the file is sent and updated anyhow. Then, if you have compression like gzipping enabled on the server, the files that are to be provided to the client must be gzipped on the way, requiring some amount of server side processing. But how is this managed? The logical approach seems to me, that the web server should have a cache as well, containing the newest version of all files that have been requested within a certain time span, thus a compressed version of these files, so that compression would not have to be done each time a files is requested. And also, how are files eventually requested? Does the browser ask for files, each time it encounters one in the HTML code and the specific file is not stored in the local cache, or does it sum all the files that are needed up and ask for the whole bunch at the same time? But that's only guessing from a programming point of view, and I don't really know. If the answers are very different among web server systems, I'm primarily interested in Apache, but other answers are appreciated, too.

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  • How can I disable the IR/Remote Control on an HP Laptop?

    - by Steve Rowe
    I've seen this happen on 2 different HP laptops now. If I try to use them in the same room as a Media Center, the MCE TV remote keeps sending commands to the laptop. This can do anything from wake it up and turn it on to just moving the selection around. There is no obvious way to disable the IR sensor or at least its response to the remote. Does anyone know how to do this?

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  • Using SQL Source Control with Fortress or Vault &ndash; Part 1

    - by AjarnMark
    I am fanatical when it comes to managing the source code for my company.  Everything that we build (in source form) gets put into our source control management system.  And I’m not just talking about the UI and middle-tier code written in C# and ASP.NET, but also the back-end database stuff, which at times has been a pain.  We even script out our Scheduled Jobs and keep a copy of those under source control. The UI and middle-tier stuff has long been easy to manage as we mostly use Visual Studio which has integration with source control systems built in.  But the SQL code has been a little harder to deal with.  I have been doing this for many years, well before Microsoft came up with Data Dude, so I had already established a methodology that, while not as smooth as VS, nonetheless let me keep things well controlled, and allowed doing my database development in my tool of choice, Query Analyzer in days gone by, and now SQL Server Management Studio.  It just makes sense to me that if I’m going to do database development, let’s use the database tool set.  (Although, I have to admit I was pretty impressed with the demo of Juneau that Don Box did at the PASS Summit this year.)  So as I was saying, I had developed a methodology that worked well for us (and I’ll probably outline in a future post) but it could use some improvement. When Solutions and Projects were first introduced in SQL Management Studio, I thought we were finally going to get our same experience that we have in Visual Studio.  Well, let’s say I was underwhelmed by Version 1 in SQL 2005, and apparently so were enough other people that by the time SQL 2008 came out, Microsoft decided that Solutions and Projects would be deprecated and completely removed from a future version.  So much for that idea. Then I came across SQL Source Control from Red-Gate.  I have used several tools from Red-Gate in the past, including my favorites SQL Compare, SQL Prompt, and SQL Refactor.  SQL Prompt is worth its weight in gold, and the others are great, too.  Earlier this year, we upgraded from our earlier product bundles to the new Developer Bundle, and in the process added SQL Source Control to our collection.  I thought this might really be the golden ticket I was looking for.  But my hopes were quickly dashed when I discovered that it only integrated with Microsoft Team Foundation Server and Subversion as the source code repositories.  We have been using SourceGear’s Vault and Fortress products for years, and I wholeheartedly endorse them.  So I was out of luck for the time being, although there were a number of people voting for Vault/Fortress support on their feedback forum (as did I) so I had hope that maybe next year I could look at it again. But just a couple of weeks ago, I was pleasantly surprised to receive notice in my email that Red-Gate had an Early Access version of SQL Source Control that worked with Vault and Fortress, so I quickly downloaded it and have been putting it through its paces.  So far, I really like what I see, and I have been quite impressed with Red-Gate’s responsiveness when I have contacted them with any issues or concerns that I have had.  I have had several communications with Gyorgy Pocsi at Red-Gate and he has been immensely helpful and responsive. I must say that development with SQL Source Control is very different from what I have been used to.  This post is getting long enough, so I’ll save some of the details for a separate write-up, but the short story is that in my regular mode, it’s all about the script files.  Script files are King and you dare not make a change to the database other than by way of a script file, or you are in deep trouble.  With SQL Source Control, you make your changes to your development database however you like.  I still prefer writing most of my changes in T-SQL, but you can also use any of the GUI functionality of SSMS to make your changes, and SQL Source Control “manages” the script for you.  Basically, when you first link your database to source control, the tool generates scripts for every primary object (tables and their indexes are together in one script, not broken out into separate scripts like DB Projects do) and those scripts are checked into your source control.  So, if you needed to, you could still do a GET from your source control repository and build the database from scratch.  But for the day-to-day work, SQL Source Control uses the same technique as SQL Compare to determine what changes have been made to your development database and how to represent those in your repository scripts.  I think that once I retrain myself to just work in the database and quit worrying about having to find and open the right script file, that this will actually make us more efficient. And for deployment purposes, SQL Source Control integrates with the full SQL Compare utility to produce a synchronization script (or do a live sync).  This is similar in concept to Microsoft’s DACPAC, if you’re familiar with that. If you are not currently keeping your database development efforts under source control, definitely examine this tool.  If you already have a methodology that is working for you, then I still think this is worth a review and comparison to your current approach.  You may find it more efficient.  But remember that the version which integrates with Vault/Fortress is still in pre-release mode, so treat it with a little caution.  I have found it to be fairly stable, but there was one bug that I found which had inconvenient side-effects and could have really been frustrating if I had been running this on my normal active development machine.  However, I can verify that that bug has been fixed in a more recent build version (did I mention Red-Gate’s responsiveness?).

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  • What version-control system is most trivial to set up and use for toy projects?

    - by Norman Ramsey
    I teach the third required intro course in a CS department. One of my homework assignments asks students to speed up code they have written for a previous assignment. Factor-of-ten speedups are routine; factors of 100 or 1000 are not unheard of. (For a factor of 1000 speedup you have to have made rookie mistakes with malloc().) Programs are improved by a sequence is small changes. I ask students to record and describe each change and the resulting improvement. While you're improving a program it is also possible to break it. Wouldn't it be nice to back out? You can see where I'm going with this: my students would benefit enormously from version control. But there are some caveats: Our computing environment is locked down. Anything that depends on a central repository is suspect. Our students are incredibly overloaded. Not just classes but jobs, sports, music, you name it. For them to use a new tool it has to be incredibly easy and have obvious benefits. Our students do most work in pairs. Getting bits back and forth between accounts is problematic. Could this problem also be solved by distributed version control? Complexity is the enemy. I know setting up a CVS repository is too baffling---I myself still have trouble because I only do it once a year. I'm told SVN is even harder. Here are my comments on existing systems: I think central version control (CVS or SVN) is ruled out because our students don't have the administrative privileges needed to make a repository that they can share with one other student. (We are stuck with Unix file permissions.) Also, setup on CVS or SVN is too hard. darcs is way easy to set up, but it's not obvious how you share things. darcs send (to send patches by email) seems promising but it's not clear how to set it up. The introductory documentation for git is not for beginners. Like CVS setup, it's something I myself have trouble with. I'm soliciting suggestions for what source-control to use with beginning students. I suspect we can find resources to put a thin veneer over an existing system and to simplify existing documentation. We probably don't have resources to write new documentation. So, what's really easy to setup, commit, revert, and share changes with a partner but does not have to be easy to merge or to work at scale? A key constraint is that programming pairs have to be able to share work with each other and only each other, and pairs change every week. Our infrastructure is Linux, Solaris, and Windows with a netapp filer. I doubt my IT staff wants to create a Unix group for each pair of students. Is there an easier solution I've overlooked? (Thanks for the accepted answer, which beats the others on account of its excellent reference to Git Magic as well as the helpful comments.)

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  • SYSTEM_HANDLE_INFORMATION structure

    - by striker
    From where does this structure originates? I know that it is declared in famous ntdll.h and is a part of undocumented windows API. But isn't it vary between different versions of windows? Is there a way to dump this structure from working system? I tried 'dt SYSTEM_HANLDE_INFORMATION' in Windbg and 'type SYSTEM_HANLDE_INFORMATION' in SoftIce but all I get is 'no such symbol' message. I also dumped ntoskrnl.pdb with PdbDump.exe and searched among the dumped structures - and could not find neither SYSTEM_HANLDE_INFORMATION nor SYSTEM_HANLDE. Could you help me?

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  • Data structure for Settlers of Catan map?

    - by templatetypedef
    Hello all- A while back someone asked me if I knew of a nice way to encode the information for the game Settlers of Catan. This would require storing a hexagonal grid in a way where each hex can have data associated with it. More importantly, though, I would need some way of efficiently looking up vertices and edges on the sides of these hexagons, since that's where all the action is. My question is this: is there a good, simple data structure for storing a hexagonal grid while allowing for fast lookup of hexagons, edges between hexagons, and vertices at the intersections of hexagons? I know that general structures like a winged-edge or quad-edge could do this, but that seems like massive overkill. Thanks!

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  • How to find out memory layout of your data structure implementation on Linux 64bit machine

    - by ajay
    In this article, http://cacm.acm.org/magazines/2010/7/95061-youre-doing-it-wrong/fulltext the author talks about the memory layouts of 2 data structures - The Binary Heap and the B-Heap and compares how one has better memory layout than the other. http://deliveryimages.acm.org/10.1145/1790000/1785434/figs/f5.jpg http://deliveryimages.acm.org/10.1145/1790000/1785434/figs/f6.jpg I want to get hands on experience on this. I have an implementation of a N-Ary Tree and I want to find out the memory layout of my data structure. What is the best way to come up with a memory layout like the one in the article? Secondly, I think it is easier to identify the memory layout if it is an array based implementation. If the implementation of a Tree uses pointers then what Tools do we have or what kind of approach is required to map it's memory layout? Thanks!

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  • Find the minimum gap between two numbers in an AVL tree

    - by user1656647
    I have a data structures homework, that in addition to the regular AVL tree functions, I have to add a function that returns the minimum gap between any two numbers in the AVL tree (the nodes in the AVL actually represent numbers.) Lets say we have the numbers (as nodes) 1 5 12 20 23 21 in the AVL tree, the function should return the minimum gap between any two numbers. In this situation it should return "1" which is |20-21| or |21-20|. It should be done in O(1). Tried to think alot about it, and I know there is a trick but just couldn't find it, I have spent hours on this. There was another task which is to find the maximum gap, which is easy, it is the difference between the minimal and maximal number.

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  • Why does forward declaration not work with classes?

    - by eSKay
    int main() { B bb; //does not compile (neither does class B bb;) C cc; //does not compile struct t tt; //compiles class B {}; struct s { struct t * pt; }; //compiles struct t { struct s * ps; }; return 0; } class C {}; I just modified the example given here. Why is that the struct forward declarations work but not the class forward declarations? Does it have something to do with the namespaces - tag namespace and typedef namespace? I know that the structure definitions without typedefs go to tag namespace. Structures are just classes with all public members. So, I expect them to behave similarly.

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  • Accessing structure through pointers [c]

    - by Blackbinary
    I've got a structure which holds names and ages. I've made a linked-list of these structures, using this as a pointer: aNode *rootA; in my main. Now i send **rootA to a function like so addElement(5,"Drew",**rootA); Because i need to pass rootA by reference so that I can edit it in other functions (in my actual program i have two roots, so return will not work) The problem is, in my program, i can't say access the structure members. *rootA->age = 4; for example doesnt work. Hopefully you guys can help me out. Thanks!

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  • Is there an existing solution to the multithreaded data structure problem?

    - by thr
    I've had the need for a multi-threaded data structure that supports these claims: Allows multiple concurrent readers and writers Is sorted Is easy to reason about Fulfilling multiple readers and one writer is a lot easier, but I really would wan't to allow multiple writers. I've been doing research into this area, and I'm aware of ConcurrentSkipList (by Lea based on work by Fraser and Harris) as it's implemented in Java SE 6. I've also implemented my own version of a concurrent Skip List based on A Provably Correct Scalable Concurrent Skip List by Herlihy, Lev, Luchangco and Shavit. These two implementations are developed by people that are light years smarter then me, but I still (somewhat ashamed, because it is amazing work) have to ask the question if these are the two only viable implementations of a concurrent multi reader/writer data structures available today?

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  • Boost::Spirit::Qi autorules -- avoiding repeated copying of AST data structures

    - by phooji
    I've been using Qi and Karma to do some processing on several small languages. Most of the grammars are pretty small (20-40 rules). I've been able to use autorules almost exclusively, so my parse trees consist entirely of variants, structs, and std::vectors. This setup works great for the common case: 1) parse something (Qi), 2) make minor manipulations to the parse tree (visitor), and 3) output something (Karma). However, I'm concerned about what will happen if I want to make complex structural changes to a syntax tree, like moving big subtrees around. Consider the following toy example: A grammar for s-expr-style logical expressions that uses autorules... // Inside grammar class; rule names match struct names... pexpr %= pand | por | var | bconst; pand %= lit("(and ") >> (pexpr % lit(" ")) >> ")"; por %= lit("(or ") >> (pexpr % lit(" ")) >> ")"; pnot %= lit("(not ") >> pexpr >> ")"; ... which leads to parse tree representation that looks like this... struct var { std::string name; }; struct bconst { bool val; }; struct pand; struct por; struct pnot; typedef boost::variant<bconst, var, boost::recursive_wrapper<pand>, boost::recursive_wrapper<por>, boost::recursive_wrapper<pnot> > pexpr; struct pand { std::vector<pexpr> operands; }; struct por { std::vector<pexpr> operands; }; struct pnot { pexpr victim; }; // Many Fusion Macros here Suppose I have a parse tree that looks something like this: pand / ... \ por por / \ / \ var var var var (The ellipsis means 'many more children of similar shape for pand.') Now, suppose that I want negate each of the por nodes, so that the end result is: pand / ... \ pnot pnot | | por por / \ / \ var var var var The direct approach would be, for each por subtree: - create pnot node (copies por in construction); - re-assign the appropriate vector slot in the pand node (copies pnot node and its por subtree). Alternatively, I could construct a separate vector, and then replace (swap) the pand vector wholesale, eliminating a second round of copying. All of this seems cumbersome compared to a pointer-based tree representation, which would allow for the pnot nodes to be inserted without any copying of existing nodes. My question: Is there a way to avoid copy-heavy tree manipulations with autorule-compliant data structures? Should I bite the bullet and just use non-autorules to build a pointer-based AST (e.g., http://boost-spirit.com/home/2010/03/11/s-expressions-and-variants/)?

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