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  • Type-safe generic data structures in plain-old C?

    - by Bradford Larsen
    I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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  • Extract elements from list based on object property type

    - by Dustin Digmann
    Often, I have a list of objects. Each object has properties. I want to extract a subset of the list where a specific property has a predefined value. Example: I have a list of User objects. A User has a homeTown. I want to extract all users from my list with "Springfield" as their homeTown. I normally see this accomplished as follows: List users = getTheUsers(); List returnList = new ArrayList(); for (User user: users) { if ("springfield".equalsIgnoreCase(user.getHomeTown()) returnList.add(user); } I am not particularly satisfied with this solution. Yes, it works, but it seems so slow. There must be a non-linear solution. Suggestions?

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  • Parallelism on two duo-core processor system

    - by Qin
    I wrote a Java program that draw the Mandelbrot image. To make it interesting, I divided the for loop that calculates the color of each pixel into 2 halves; each half will be executed as a thread thus parallelizing the task. On a two core one cpu system, the performance of using two thread approach vs just one main thread is nearly two fold. My question is on a two dual-core processor system, will the parallelized task be split among different processor instead of just utilize the two core on one processor? I suppose the former scenario will be slower than the latter one simply because the latency of communicating between 2 CPU over the motherboard wires. Any ideas? Thanks

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  • postgres - group by on multiple columns - master/detail type table

    - by smpillay
    I have a table order(orderid, ordernumber, clientid, orderdesc etc.,) and a corresponding status for that order on an order_status table ( statusid, orderid, statusdesc, statusNote, statustimestamp) say I have a record in order as below orderid orderumber clientid orderdesc 1111 00980065 ABC blah..blah.. and a corresponding status entries statusid orderid statusdesc statusNote statustimestamp 11 1111 recvd status blah yyyy-mm-dd:10:00 12 1111 clientproce status blah yyyy-mm-dd:11:00 13 1111 clientnotice status blah yyyy-mm-dd:15:00 14 1111 notified status blah yyyy-mm-dd:17:00 How can I get the following result (latest timestamp along with multiple columns) 1111 14 00980065 ABC blah..blah.. notified status blah yyyy-mm-dd:17:00

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  • Measuring execution time of a call to system() in C++

    - by jm1234567890
    I have found some code on measuring execution time here http://www.dreamincode.net/forums/index.php?showtopic=24685 However, it does not seem to work for calls to system(). I imagine this is because the execution jumps out of the current process. clock_t begin=clock(); system(something); clock_t end=clock(); cout<<"Execution time: "<<diffclock(end,begin)<<" s."<<endl; Then double diffclock(clock_t clock1,clock_t clock2) { double diffticks=clock1-clock2; double diffms=(diffticks)/(CLOCKS_PER_SEC); return diffms; } However this always returns 0 seconds... Is there another method that will work? Also, this is in Linux. Thanks!

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  • Response.Redirect causes System.Threading.ThreadAbortException

    - by RandomBen
    When I use Response.Redirect(...) to redirect my form to a new page I get the error: A first chance exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll An exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll but was not handled in user code My understanding of this is that the error is being caused by the webserver aborting the remainder of the page the response.redirect was called on. I know I can add a second parameter to Response.Redirect that is called endResponse. If I set endResponse to True I still get the error but if I set it to False then I do not. I am pretty sure though that that means the webserver is running the rest of the page I redirected away from. Which would seem to be inefficient to say the least. Is there a better way to do this? Something other than Response.Redirect or is there a way to force the old page to stop loading where I will not get a ThreadAbortException?

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  • Behaviour of System.Timer when Interval property changed

    - by lowlyintern
    I have a System.Timer setup to trigger an event every day at 2AM. If the process the timer starts fails then I want the timer to be reset to run every 15 minutes until the process completes succesfully. // this is how the timer is set up. // this is working correctly. double startTime = milliseconds_of_hour_to_start. Timer = new System.Timers.Timer( startTime); Here is the code to reset the timer on success or failure of the event handler. NOTE the timer is not being stopped, just the Interval property is being reset. if (ProcessSuccess) { Timer.Interval = TimeSpan.FromHours(24).TotalMilliseconds; } else { Timer.Interval = TimeSpan.FromMinutes(15).TotalMilliseconds; } My question is this, if the process fails say 4 times, then succeeds will the Timer now be running at around 3AM? i.e. after failing will the original start time of 2AM be advanced by 15 minutes?

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  • Make conversion to a native type explicit in C++

    - by Tal Pressman
    I'm trying to write a class that implements 64-bit ints for a compiler that doesn't support long long, to be used in existing code. Basically, I should be able to have a typedef somewhere that selects whether I want to use long long or my class, and everything else should compile and work. So, I obviously need conversion constructors from int, long, etc., and the respective conversion operators (casts) to those types. This seems to cause errors with arithmetic operators. With native types, the compiler "knows" that when operator*(int, char) is called, it should promote the char to int and call operator*(int, int) (rather than casting the int to char, for example). In my case it gets confused between the various built-in operators and the ones I created. It seems to me like if I could flag the conversion operators as explicit somehow, that it would solve the issue, but as far as I can tell the explicit keyword is only for constructors (and I can't make constructors for built-in types). So is there any way of marking the casts as explicit? Or am I barking up the wrong tree here and there's another way of solving this? Or maybe I'm just doing something else wrong...

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  • Mac OS X - detect file system read

    - by quano
    I want to know what files a specific application is trying to access on my disk. I know that you can use fs_usage, but this outputs events from all applications. I know that you can target a single application, but only one that is already running. I want to detect all readfile-events an application is trying to do, ever since it is started. I don't want to miss out on any event. How do you achieve this?

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  • ASP.NET - How to edit 'bit' data type?

    - by Peter
    I am coding in Visual Basic. I am using a checkbox control. Now depending on its checked property I need to set/unset a bit column in a SQL Server database. Here's the code: Try conSQL.Open() Dim cmd As New SqlCommand("update Student set send_mail = " + _ sendemailCheckBox.Checked.ToString + " where student_id = '" _ + sidnolabel.Text + "'", conSQL) cmd.ExecuteNonQuery() Finally conSQL.Close() End Try The send_mail attribute is of bit datatype. This code is not working. How do I go about it?

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  • Recommended laptops for system admins?

    - by 80skeys
    Hey all - I'm in the market for a new laptop and wanted to get some recommendations. I'm a Linux sysadmin and this laptop is primarily for work related use, working from home, after hours, occasional trips to the data center, etc. We all know the drill. My typical setup includes various utilities and tools plus multiple partitions for booting different OS's including VMware. Need serial port of course, DVD-RW, and all the usual stuff we use in our daily routine. I'm kinda thinking a Thinkpad T510 but open to other suggestions! Brief explanation of why you suggest some particular brand and configuration is appreciated.

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  • Why can I derived from a templated/generic class based on that type in C# / C++

    - by stusmith
    Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

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  • C++ Type error with Object versus Object reference

    - by muddybruin
    I have the following function (which worked in Visual Studio): bool Plane::contains(Vector& point){ return normalVector.dotProduct(point - position) < -doubleResolution; } When I compile it using g++ version 4.1.2 , I get the following error: Plane.cpp: In member function âvirtual bool Plane::contains(Vector&)â: Plane.cpp:36: error: no matching function for call to âVector::dotProduct(Vector)â Vector.h:19: note: candidates are: double Vector::dotProduct(Vector&) So as you can see, the compiler thinks (point-position) is a Vector but it's expecting Vector&. What's the best way to fix this? I verified that this works: Vector temp = point-position; return normalVector.dotProduct(temp) < -doubleResolution; But I was hoping for something a little bit cleaner. I heard a suggestion that adding a copy constructor might help. So I added a copy constructor to Vector (see below), but it didn't help. Vector.h: Vector(const Vector& other); Vector.cpp: Vector::Vector(const Vector& other) :x(other.x), y(other.y), z(other.z), homogenous(other.homogenous) { }

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  • Can someone explain Kohana 3's routing system?

    - by alex
    In bootstrap.php, where you set routes, I'm having a hard time getting them to work. I read some documentation a while ago that I can't seem to find again that explains them. Here is one of my examples Route::set('products', 'products/(type)', array('type' => '.+')) ->defaults(array( 'controller' => 'articles', 'action' => 'view_product', 'page' => 'shock-absorbers', )); I thought that would mean a request like products/something would load up the articles controller, and the action_view_product method. But I can't get it to work. Can someone please explain to me exactly how they work, and what all the method parameters are?

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  • system-wide hook for 64-bit operating systems

    - by strDisplayName
    Hey everybody I want to perform a system-wide hook (using SetWindowHook) on a 64bit operating system. I know that 64bit processes (= proc64) can load only 64bit dlls (= dll64) and 32bit processes (= proc32) can load only 32bit dlls (= dll32). Currently I am planning to call SetWindowHook twice, once with dll32 and once with dll64, expecting that proc64s will load dll64 and proc32s will load dll32 (while dll32 for proc64s and dll64 for proc32s will fail). Is that the correct way to do that, or is there a "more correct" way to do that? Thanks! :-)

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  • How to pass parameters with spaces via cstdlib system

    - by buchtak
    Hi, I have this windows console app which takes a file, do some calculations, and then writes the output to a specified file. The input is specified in "app.exe -input fullfilename" format. I need to call this application from my C++ program, but I have a problem with spaces in paths to files. When I call the app directly from cmd.exe by typing (without specifying output file for clarity) "c:\first path\app.exe" -input "c:\second path\input.file" everything works as expected. But, when I try using cstdlib std::system() function, i.e. std::system(" \"c:\\first path\\app.exe\" -input \"c:\\second path\\input.file\" "); the console prints out that c:\first is not any valid command. It's probably common mistake and has simple solution, but I have been unable to find any. Thx for any help.

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  • System requirements for running windows 8 (basic office use) in virtualbox (ubuntu as host os)

    - by Tor Thommesen
    I want to run windows 8 as a guest os with virtualbox on some thinkpad (haven't bought one yet) running Ubuntu 12.04. Apart from virtualizing windows 8 (mostly just for use with the office suite app) my needs are very modest, I don't need much more than emacs and a browser. What I'd like to know is what kind of specs will be necessary to run windows 8 well as a vm, using the office apps. It would be a shame to waste money on overpowered hardware. Are there any official guidelines from oracle or windows on this? Would this lenovo x220, for example, be sufficiently strong? The specs below were taken from this review. Intel Core i5-2520M dual-core processor (2.5GHz, 3MB cache, 3.2GHz Turbo frequency) Windows 7 Professional (64-bit) 12.5-inch Premium HD (1366 x 768) LED Backlit Display (IPS) Intel Integrated HD Graphics 4GB DDR3 (1333MHz) 320GB Hitachi Travelstar hard drive (Z7K320) Intel Centrino Advanced-N 6205 (Taylor Peak) 2x2 AGN wireless card Intel 82579LM Gigabit Ethernet 720p High Definition webcam Fingerprint reader 6-cell battery (63Wh) and optional slice battery (65Wh) Dimensions: 12 (L) x 8.2 (W) x 0.5-1.5 (H) inches with 6-cell battery Weight: 3.5 pounds with 6-cell battery 4.875 pounds with 6-cell battery and optional external battery slice Price as configured: $1,299.00 (starting at $979.00)

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  • C++ return type overload hack

    - by aaa
    I was bored and came up with such hack (pseudocode): 1 struct proxy { 2 operator int(); // int function 3 operator double(); // double function 4 proxy(arguments); 5 arguments &arguments_; 6 }; 7 8 proxy function(arguments &args) { 9 return proxy(args); 10 } 11 int v = function(...); 12 double u = function(...); is it evil to use in real code?

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  • 9gag type of website

    - by awtasdfas
    for something like www.9gag.com , which open source mvc framework can be used? in particular the main page, with highly rated content is what i am looking for.. along with an option for users to thumbs up/heart every article/post/blog/vlog/podcast/link.

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