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• Flickering dual screens in Virtual Box Ubuntu 13.10 Guest

  - by alexleonard

  I have Ubuntu 13.10 x64 installed as a guest in VirtualBox (under a Windows 8.1 host) and have the settings for the virtual machine setup to run with a monitor count of 2, 128MB video memory and 3D acceleration enabled. In my guest I have the virtual box additions installed (which allowed me to have two 1920x1080 screens). Here's a screenshot of my VM settings. My laptop is an Asus N550JV which has both Intel's HD Graphics 4600 GPU and Nvidia's GeForce GT 750M. By default though I believe the Intel GFX card is being used to render the VM. When I boot up the VM it loads perfectly on dual screens, however whenever I move the mouse from one screen to the other (I have a Dell S2340L running over a HDMI connection as a second screen) the screen flickers. I've tried a variety of settings changes in both Ubuntu and the VM settings, but cannot seem to stop this screen flicker. I also used the NVidia control panel in Windows to force the dedicated graphics card to always be used but found that the display driver sometimes crashed whilst working in the VM, resulting in my VM session being destroyed, so I figured it's better to stick with the Intel GFX as that appears to be more stable. I also tried without 3D acceleration but that was much worse, and if I ran the VM with a low amount of graphics memory it really struggled. Here's my dmesg output: http://pastebin.com/1LJuYWMj (not sure if this is helpful in this situation). I read some posts suggesting changes to /etc/X11/xorg.conf but I don't appear to have an xorg.conf file. There were also a few posts (though related to Synergy) suggesting running xset -dpms but this command doesn't appear to have had any effect for me. As an additional note, I'm finding that window drawing in the guest is a little laggy/glitchy. For example, quickly scrolling through a web page may result in parts of the viewport displaying original content. Certainly I notice drawing issues most in the web browser, but it also impacts other software with parts of the window not being drawn when, say, switching between accounts in thunderbird. Any suggestions greatly appreciated!

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• Updating ASUS BIOS on Windows 7 64bit

  - by joesavage

  I've recently decided that I want to try and utilize my two graphics cards so that I can have a dual monitor setup. Unfortunately Windows only seems to notice my most recent graphics card installation - and so I've been told that I should look into my BIOS and try to enable two graphics cards. I could not find this setting anywhere in my M2N68-AM Plus v0210 BIOS. After some further research I figured that I should perhaps upgrade my BIOS, so I searched and managed to download the latest version (v1804) as a ROM file. However I am having difficulty figuring out how to install it. I've tried using the Asus EZFlash feature built into my BIOS, but when trying to load up a variety of different ROMs that are for my motherboard/BIOS I get the error: Boot block in file is not valid! I'm not totally sure what I should do to fix this, so I'm looking into other methods of upgrading my BIOS - however I can't really find any solutions that seem to work. Asus Update is for 32-bit only, AFUDOS doesn't appear to work on my Windows 7 64-bit system (I think it's supposed to run in DOS or something - but that just sounds confusing since I know nothing about DOS). Could anybody help me with this?

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• Upgrade or replace?

  - by Felix

  My current PC is about four years old, although I have made upgrades to it throughout its existence. The current specs are: (old) Intel Pentium D 2.80Ghz (32K L1 / 2M L2), Gigabyte 945GCMX-S2 motherboard (old) 2.5GB DDR2 (slot0: 512MB @ 533Mhz; slot1: 2GB @ 667Mhz) (new) HIS Radeon HD 4670 - I think this is limited by the motherboard not supporting PCIe 2.0 (?) (old) WD Caviar 160GB - pretty slow (new) WD Caviar Black 640GB (if any more specs are relevant, let me know and I'll add them) Now, on to my question. I've been having performance issues lately, both in video games and in intensive applications. A couple of examples: Android application development (running Eclipse and the Android emulator) is painfully slow (on Linux). I only realized this when, at my new job as an Android dev, both tools are MUCH quicker. (I'm not sure what CPU I have there) The guys at my new job got me NFS Hot Pursuit, in which I barely get like 5-10FPS, even with graphics options turned all the way down My guess is that the bottleneck in my system is my CPU, so I'm thinking of upgrading to a Quad Core i5 + new motherboard + 4GB DDR3 (or more, 'cause I know you'll all jump and say 8GB minimum). Now: Is that a good idea? Is my CPU really a bottleneck, or is the whole system too old and I should replace it? I run Windows 7 on the old, 160GB HDD (which is on IDE, by the way). Could this slow down games as well? Should I get a new drive for Windows if I want to play new games? I know nothing about power supplies. Could that be a problem / will it be a problem if I upgrade to an i5? How come DiRT2 works on full graphics settings (pretty amazing graphics by the way) and NFS Hot Pursuit pulls only 5-10FPS?

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• How to disable monitor auto detection in Windows 7?

  - by Jay Yother

  I am currently running Windows 7 Ultimate 64-bit with a dual monitor setup with an NVIDIA 7950 GT graphics card. One monitor is dedicated to this machine and the other monitor is connected to a DVI KVM switch. When I switch to my other computer, Windows 7 disables the monitor. However, when I switch back it does not re-enable the monitor. The only circumstance that automatically re-enables the second monitor is when I switch back after Windows has put the monitors into power save mode. I am continually having to bring up the NVIDIA control panel to have it re-enable the monitor. Under Windows XP I would just disable the NVIDIA service to prevent it from auto-detecting the monitor (which doesn't solve the problem under Win7), and in Vista there was a registry hack that would prevent this. It looks as though that has been removed in Windows 7. I have found similar questions posted on this site, but nothing that matches my problem exactly. The following link is the question that comes the closest, but does not provide a solution to the problem. http://superuser.com/questions/96683/how-to-fix-monitor-detection-on-windows-7 Is there a way in Windows 7 to disable monitor auto-detection? Update: I just added a second graphics card to my Windows 7 64-bit machine. I plugged one monitor into each graphics card. Now, when I use the KVM switch to switch back and forth it will re-enable the second monitor like it should. There are however, a few quirks with this. If I have a program maximized on the second monitor and it has focus, when I switch it will move to monitor 1. If I have a program maximized on the second monitor and it does not have focus, when I switch it will behave like it is minimized and when I bring it back up it will show up maximized on monitor 1. Definitely better than it was, but still looking for a way to disable the auto-detection.

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• Computer freezes after watching Youtube videos

  - by Roberts

  I had Windows 7 installed all september. But I installed Windows XP Professional back because my computer couldn't handle the new OS. After first boot I tried to install newest flash player (from Adobe website), but it failed. I had my old setup on USB drive and it worked. I don't know is it important or not. I am watching Youtube videos in my free time (almost every hour). After few days the computer started to freeze when I open a page with the video or close the page with video, not while I watch a video. No BSODs. Nothing in Event viewer. I use Firefox only. When computer freezes the sound wont. If iTunes is playing a radio station or is it another video playing in background, the sound wont freeze. Last few days the mouse wont freeze. Its a strange symptom. If I click few times then the cursor will actually freeze. I just want to know where does this problem come from (hardware - graphics card, old motherboard or it's just some glitch in setups). If it's not graphics card then I will be happy. The graphics card is ATI Radeon HD 4650 - brand new. Catalyst 11.8 installed. Things I have tried: Installed newest flash player after a week (the setup didn't fail this time) Installed latest video drivers Deleting cookies Defragmenting hard drive Using TuneUp utilities for computer cleenup Installed latest Mozilla Firefox Cleaned the PC Changed CPU Fan speed almost to max (just to be sure) Things I haven't tried yet: Didn't try playing videos on other browsers What can I do now?

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• Image Management System with Different Levels of Access

  - by Jason

  I work in the graphics department for a real estate brokerage, and we deal with a lot of photos. Agents take the photos, upload them to me, I touch up and standardize the photos, then I add them to an in-house server for future use by the graphics dept. I'd like to make the "sanitized" photo files available to the agents to use when they want, but I don't want the agents poking around the graphics department's files (things get misplaced, renamed and messed up in a hurry). What would be perfect is if we could create a read-only "mirror" (correct term?) of that server that could be accessed by the agents as needed, but which wouldn't feed back into our "sanitized" file system. Edit: I'm looking for an automatic solution... manually posting the files to two separate locations seems like an inelegant solution when working digitally. Edit: I'm trying to avoid any access barriers to the public (dirty) file system (however it's finally implemented). There are 40-50 real estate agents who need to access these files, half of whom can't reliably download an email attachment.

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• Windows 8 doesn't start up after installation

  - by Raj BD

  I have a DELL INSPIRON n5110 machine running Windows 7 Home Premium 64-bit. It has 6GB of RAM and 500 GB hard disk capable to run any Windows and Linux system. And I recently attempted to install Windows 8 in the machine. Installation goes fine and smooth until the final stage when windows is done installing and GETS DEVICES READY. When GETTNG DEVICES READY reaches about 60%, the screen goes blank with the machine running. After a while it reboots. And after the new Windows Logo with dotted circles are done showing up, the screen goes blank again (when we'd expect login screen to show up). There is not even a cursor. I can see the HARD DISK ACTIVITY LED blinking but nothing shows up in the screen. I've tried CLEAN INSTALL several times. The DVD is fine, it installed and worked well in my friends' laptop PCs. I tried installing both PRO version and ENTERPRISE version and both 32-bit and 64-bit. But the problem was same everytime. Finally, I had to reinstall Windows 7 which installed and ran without any problem. The problem, we can guess, is GRAPHICS perhaps. I have Intel SandyBridge Graphics Mobile Chipset (Intel HD Graphics 3000). But if Windows 7 and Linux distrubutions like Mint and BackTrack can run on the machine, why on earth, would Windows 8 not run?

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• Android Canvas Coordinate System

  - by Mitch

  I'm trying to find information on how to change the coordinate system for the canvas. I have some vector data I'd like to draw to a canvas using things like circles and lines, but the data's coordinate system doesn't match the canvas coordinate system. Is there a way to map the units I'm using to the screen's units? I'm drawing to an ImageView which isn't taking up the entire display. If I have to do my own calculations prior to each drawing call, how to I find the width and height of my ImageView? The getWidth() and getHeight() calls I tried seem to be returning the entire canvas size and not the size of the ImageView which isn't helpful. I see some matrix stuff, is that something that will work for me? I tried to use the "public void scale(float sx, float sy)", but that works more like a pixel level zoom rather than a vector scale function by expanding each pixel. This means if the dimensions are increased to fit the screen, the line thickness is also increased. Update: After some research I'm starting to think there's no way to change coordinate systems to something else. I'll need to map all my coordinates to the screen's pixel coordinates and do so by modifying each vector. The getWidth() and getHeight() seem to be working better for me now. I can say what was wrong, but I suspect I can't use these methods inside the constructor.

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• boost.serialization and lazy initialization

  - by niXman

  i need to serialize directory tree. i have no trouble with this type: std::map< std::string, // string(path name) std::vector<std::string> // string array(file names in the path) > tree; but for the serialization the directory tree with the content i need other type: std::map< std::string, // string(path name) std::vector< // files array std::pair< std::string, // file name std::vector< // array of file pieces std::pair< // <<<<<<<<<<<<<<<<<<<<<< for this i need lazy initialization std::string, // piece buf boost::uint32_t // crc32 summ on piece > > > > > tree; how can i serialize the object of type "std::pair" in the moment of its serialization?

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• Context migration in CUDA.NET

  - by Vyacheslav

  I'm currently using CUDA.NET library by GASS. I need to initialize cuda arrays (actually cublas vectors, but it doesn't matters) in one CPU thread and use them in other CPU thread. But CUDA context which holding all initialized arrays and loaded functions, can be attached to only one CPU thread. There is mechanism called context migration API to detach context from one thread and attach it to another. But i don't how to properly use it in CUDA.NET. I tried something like this: class Program { private static float[] vector1, vector2; private static CUDA cuda; private static CUBLAS cublas; private static CUdeviceptr ptr; static void Main(string[] args) { cuda = new CUDA(false); cublas = new CUBLAS(cuda); cuda.Init(); cuda.CreateContext(0); AllocateVectors(); cuda.DetachContext(); CUcontext context = cuda.PopCurrentContext(); GetVectorFromDeviceAsync(context); } private static void AllocateVectors() { vector1 = new float[]{1f, 2f, 3f, 4f, 5f}; ptr = cublas.Allocate(vector1.Length, sizeof (float)); cublas.SetVector(vector1, ptr); vector2 = new float[5]; } private static void GetVectorFromDevice(object objContext) { CUcontext localContext = (CUcontext) objContext; cuda.PushCurrentContext(localContext); cuda.AttachContext(localContext); //change vector somehow vector1[0] = -1; //copy changed vector to device cublas.SetVector(vector1, ptr); cublas.GetVector(ptr, vector2); CUDADriver.cuCtxPopCurrent(ref localContext); } private static void GetVectorFromDeviceAsync(CUcontext cUcontext) { Thread thread = new Thread(GetVectorFromDevice); thread.IsBackground = false; thread.Start(cUcontext); } } But execution fails on attempt to copy changed vector to device because context is not attached? Any ideas how i can get it work?

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• Ruby on Rails: How to sanitize a string for SQL when not using find?

  - by williamjones

  I'm trying to sanitize a string that involves user input without having to resort to manually crafting my own possibly buggy regex if possible, however, if that is the only way I would also appreciate if anyone can point me in the right direction to a regex that is unlikely to be missing anything. There are a number of methods in Rails that can allow you to enter in native SQL commands, how do people escape user input for those? The question I'm asking is a broad one, but in my particular case, I'm working with a column in my Postgres database that Rails does not natively understand as far as I know, the tsvector, which holds plain text search information. Rails is able to write and read from it as if it's a string, however, unlike a string, it doesn't seem to be automatically escaping it when I do things like vector= inside the model. For example, when I do model.name='::', where name is a string, it works fine. When I do model.vector='::' it errors out: ActiveRecord::StatementInvalid: PGError: ERROR: syntax error in tsvector: "::" "vectors" = E'::' WHERE "id" = 1 This seems to be a problem caused by lack of escaping of the semicolons, and I can manually set the vector='\:\:' fine. I also had the bright idea, maybe I can just call something like: ActiveRecord::Base.connection.execute "UPDATE medias SET vectors = ? WHERE id = 1", "::" However, this syntax doesn't work, because the raw SQL commands don't have access to find's method of escaping and inputting strings by using the ? mark. This strikes me as the same problem as calling connection.execute with any type of user input, as it all boils down to sanitizing the strings, but I can't seem to find any way to manually call Rails' SQL string sanitization methods. Can anyone provide any advice?

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• Why is the compiler not selecting my function-template overload in the following example?

  - by Steve Guidi

  Given the following function templates: #include <vector> #include <utility> struct Base { }; struct Derived : Base { }; // #1 template <typename T1, typename T2> void f(const T1& a, const T2& b) { }; // #2 template <typename T1, typename T2> void f(const std::vector<std::pair<T1, T2> >& v, Base* p) { }; Why is it that the following code always invokes overload #1 instead of overload #2? void main() { std::vector<std::pair<int, int> > v; Derived derived; f(100, 200); // clearly calls overload #1 f(v, &derived); // always calls overload #1 } Given that the second parameter of f is a derived type of Base, I was hoping that the compiler would choose overload #2 as it is a better match than the generic type in overload #1. Are there any techniques that I could use to rewrite these functions so that the user can write code as displayed in the main function (i.e., leveraging compiler-deduction of argument types)?

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• Changing JButton background colour temporarily?

  - by sashep

  Hi, I'm super new to Java, and in need of some help. I'm making a little java desktop application where I basically have a grid of 4 JButtons ( 2 x 2 grid), and I need the background colour of individual JButtons to change, and after one second, change back to the original colour (the game I'm trying to make is like Simon, where you have to follow a pattern of buttons that light up). I have a vector that contains randomly generated numbers in the range of 1 to 4, and I want to be able to get each element from the vector and get the corresponding button to change to a different colour for one second (for example, if the vector contains 2 4 1, I would want button 2 to change, then button 4 to change, then button 1 to change). Is this possible or is there a better way to go about doing this with something other than JButtons? How do I implement this? Also, I'm running Mac OS X, which apparently (based on some things I've read on forums) doesn't like JButtons background changing (I think it's because of system look and feel), how can I change this so it works on mac? Thank you in advance for any help :)

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• [ActionScript 3] Array subclasses cannot be deserialized, Error #1034

  - by aaaidan

  I've just found a strange error when deserializing from a ByteArray, where Vectors cannot contain types that extend Array: there is a TypeError when they are deserialized. TypeError: Error #1034: Type Coercion failed: cannot convert []@4b8c42e1 to com.myapp.ArraySubclass. at flash.utils::ByteArray/readObject() at com.myapp::MyApplication()[/Users/aaaidan/MyApp/com/myapp/MyApplication.as:99] Here's how: public class Application extends Sprite { public function Application() { // register the custom class registerClassAlias("MyArraySubclass", MyArraySubclass); // write a vector containing an array subclass to a byte array var vec:Vector.<MyArraySubclass> = new Vector.<MyArraySubclass>(); var arraySubclass:MyArraySubclass = new MyArraySubclass(); arraySubclass.customProperty = "foo"; vec.push(arraySubclass); var ba:ByteArray = new ByteArray(); ba.writeObject(arraySubclass); ba.position = 0; // read it back var arraySubclass2:MyArraySubclass = ba.readObject() as MyArraySubclass; // throws TypeError } } public class MyArraySubclass extends Array { public var customProperty:String = "default"; } It's a pretty specific case, but it seems very odd to me. Anyone have any ideas what's causing it, or how it could be fixed?

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• Ruby on Rails: How to sanitize a string for SQL when not using find and other built-in methods?

  - by williamjones

  I'm trying to sanitize a string that involves user input without having to resort to manually crafting my own possibly buggy regex if possible. There are a number of methods in Rails that can allow you to enter in native SQL commands, how do people escape user input for those? The question I'm asking is a broad one, but in my particular case, I'm working with a column in my Postgres database that Rails does not natively understand as far as I know, the tsvector, which holds plain text search information. Rails is able to write and read from it as if it's a string, however, unlike a string, it doesn't seem to be automatically escaping it when I do things like vector= inside the model. For example, when I do model.name='::', where name is a string, it works fine. When I do model.vector='::' it errors out: ActiveRecord::StatementInvalid: PGError: ERROR: syntax error in tsvector: "::" "vectors" = E'::' WHERE "id" = 1 This seems to be a problem caused by lack of escaping of the semicolons, and I can manually set the vector='\:\:' fine. I also had the bright idea, maybe I can just call something like: ActiveRecord::Base.connection.execute "UPDATE medias SET vectors = ? WHERE id = 1", "::" However, this syntax doesn't work, because the raw SQL commands don't have access to find's method of escaping and inputting strings by using the ? mark. This strikes me as the same problem as calling connection.execute with any type of user input, as it all boils down to sanitizing the strings, but I can't seem to find any way to manually call Rails' SQL string sanitization methods. Can anyone provide any advice?

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• How to count term frequency for set of documents?

  - by ManBugra

  i have a Lucene-Index with following documents: doc1 := { caldari, jita, shield, planet } doc2 := { gallente, dodixie, armor, planet } doc3 := { amarr, laser, armor, planet } doc4 := { minmatar, rens, space } doc5 := { jove, space, secret, planet } so these 5 documents use 14 different terms: [ caldari, jita, shield, planet, gallente, dodixie, armor, amarr, laser, minmatar, rens, jove, space, secret ] the frequency of each term: [ 1, 1, 1, 4, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1 ] for easy reading: [ caldari:1, jita:1, shield:1, planet:4, gallente:1, dodixie:1, armor:2, amarr:1, laser:1, minmatar:1, rens:1, jove:1, space:2, secret:1 ] What i do want to know now is, how to obtain the term frequency vector for a set of documents? for example: Set<Documents> docs := [ doc2, doc3 ] termFrequencies = magicFunction(docs); System.out.pring( termFrequencies ); would result in the ouput: [ caldari:0, jita:0, shield:0, planet:2, gallente:1, dodixie:1, armor:2, amarr:1, laser:1, minmatar:0, rens:0, jove:0, space:0, secret:0 ] remove all zeros: [ planet:2, gallente:1, dodixie:1, armor:2, amarr:1, laser:1 ] Notice, that the result vetor contains only the term frequencies of the set of documents. NOT the overall frequencies of the whole index! The term 'planet' is present 4 times in the whole index but the source set of documents only contains it 2 times. A naive implementation would be to just iterate over all documents in the docs set, create a map and count each term. But i need a solution that would also work with a document set size of 100.000 or 500.000. Is there a feature in Lucene i can use to obtain this term vector? If there is no such feature, how would a data structure look like someone can create at index time to obtain such a term vector easily and fast? I'm not that Lucene expert so i'am sorry if the solution is obvious or trivial.

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• Computing complex math equations in python

  - by dassouki

  Are there any libraries or techniques that simplify computing equations ? Take the following two examples: F = B * { [ a * b * sumOf (A / B ''' for all i ''' ) ] / [ sumOf(c * d * j) ] } where: F = cost from i to j B, a, b, c, d, j are all vectors in the format [ [zone_i, zone_j, cost_of_i_to_j], [..]] This should produce a vector F [ [1,2, F_1_2], ..., [i,j, F_i_j] ] T_ij = [ P_i * A_i * F_i_j] / [ SumOf [ Aj * F_i_j ] // j = 1 to j = n ] where: n is the number of zones T = vector [ [1, 2, A_1_2, P_1_2], ..., [i, j, A_i_j, P_i_j] ] F = vector [1, 2, F_1_2], ..., [i, j, F_i_j] so P_i would be the sum of all P_i_j for all j and Aj would be sum of all P_j for all i I'm not sure what I'm looking for, but perhaps a parser for these equations or methods to deal with multiple multiplications and products between vectors? To calculate some of the factors, for example A_j, this is what i use from collections import defaultdict A_j_dict = defaultdict(float) for A_item in TG: A_j_dict[A_item[1]] += A_item[3] Although this works fine, I really feel that it is a brute force / hacking method and unmaintainable in the case we want to add more variables or parameters. Are there any math equation parsers you'd recommend? Side Note: These equations are used to model travel. Currently I use excel to solve a lot of these equations; and I find that process to be daunting. I'd rather move to python where it pulls the data directly from our database (postgres) and outputs the results into the database. All that is figured out. I'm just struggling with evaluating the equations themselves. Thanks :)

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• Matlab - Propagate points orthogonally on to the edge of shape boundaries

  - by Graham

  Hi I have a set of points which I want to propagate on to the edge of shape boundary defined by a binary image. The shape boundary is defined by a 1px wide white edge. I also have the coordinates of these points stored in a 2 row by n column matrix. The shape forms a concave boundary with no holes within itself made of around 2500 points. I want to cast a ray from each point from the set of points in an orthogonal direction and detect at which point it intersects the shape boundary at. What would be the best method to do this? Are there some sort of ray tracing algorithms that could be used? Or would it be a case of taking orthogonal unit vector and multiplying it by a scalar and testing after multiplication if the end point of the vector is outside the shape boundary. When the end point of the unit vector is outside the shape, just find the point of intersection? Thank you very much in advance for any help!

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• How much of STL is too much?

  - by Darius Kucinskas

  I am using a lot of STL code with std::for_each, bind, and so on, but I noticed that sometimes STL usage is not good idea. For example if you have a std::vector and want to do one action on each item of the vector, your first idea is to use this: std::for_each(vec.begin(), vec.end(), Foo()) and it is elegant and ok, for a while. But then comes the first set of bug reports and you have to modify code. Now you should add parameter to call Foo(), so now it becomes: std::for_each(vec.begin(), vec.end(), std::bind2nd(Foo(), X)) but that is only temporary solution. Now the project is maturing and you understand business logic much better and you want to add new modifications to code. It is at this point that you realize that you should use old good: for(std::vector::iterator it = vec.begin(); it != vec.end(); ++it) Is this happening only to me? Do you recognise this kind of pattern in your code? Have you experience similar anti-patterns using STL?

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• Transfer data between C++ classes efficiently

  - by David

  Hi, Need help... I have 3 classes, Manager which holds 2 pointers. One to class A another to class B . A does not know about B and vise versa. A does some calculations and at the end it puts 3 floats into the clipboard. Next, B pulls from clipboard the 3 floats, and does it's own calculations. This loop is managed by the Manager and repeats many times (iteration after iteration). My problem: Now class A produces a vector of floats which class B needs. This vector can have more than 1000 values and I don't want to use the clipboard to transfer it to B as it will become time consumer, even bottleneck, since this behavior repeats step by step. Simple solution is that B will know A (set a pointer to A). Other one is to transfer a pointer to the vector via Manager But I'm looking for something different, more object oriented that won't break the existent separation between A and B Any ideas ? Many thanks David

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• Android - Correspondence between ImageView coordinates and Bitmap Pixels

  - by Matteo

  In my application I want the user to be able to select some content of an Image contained inside an ImageView. To select the content I subclassed the ImageView class making it implement the OnTouchListener so to draw over it a rectangle with borders decided by the user. Here is an example of the result of the drawing (to have an idea you can think of it as when you click with the mouse on your desktop and drag the mouse): Now I need to determine which pixels of the Bitmap image correspond to the selected part. It's kind of easy to determine which are the points of the ImageView belonging to the rectangle, but I don't know how to get the correspondent pixels, since the ImageView has a different aspect ratio than the original image. I followed the approach described especially here, but also here, but am not fully satisfied because in my opinion the correspondence made is 1 on 1 between pixels and points on the ImageView and does not give me all the correspondent pixels on the original image to the selected area. Calling hoveredRect the rectangle on the ImageView the points inside of it are: class Point { float x, y; @Override public String toString() { return x + ", " + y; } } Vector<Point> pointsInRect = new Vector<Point>(); for( int x = hoveredRect.left; x <= hoveredRect.right; x++ ){ for( int y = hoveredRect.top; y <= hoveredRect.bottom; y++ ){ Point pointInRect = new Point(); pointInRect.x = x; pointInRect.y = y; pointsInRect.add(pointInRect); } } How can I obtain a Vector<Pixels> pixelsInImage containing the correspondent pixels?

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• Mixing c++ standard strings and windows API

  - by JB

  Many windows APIs take a pointer to a buffer and a size element but the result needs to go into a c++ string. (I'm using windows unicode here so they are wstrings) Here is an example :- #include <iostream> #include <string> #include <vector> #include <windows.h> using namespace std; // This is the method I'm interested in improving ... wstring getComputerName() { vector<wchar_t> buffer; buffer.resize(MAX_COMPUTERNAME_LENGTH+1); DWORD size = MAX_COMPUTERNAME_LENGTH; GetComputerNameW(&buffer[0], &size); return wstring(&buffer[0], size); } int main() { wcout << getComputerName() << "\n"; } My question really is, is this the best way to write the getComputerName function so that it fits into C++ better, or is there a better way? I don't see any way to use a string directly without going via a vector unless I missed something? It works fine, but somehow seems a little ugly. The question isn't about that particular API, it's just a convenient example.

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• Accessing Members of Containing Objects from Contained Objects.

  - by Bunkai.Satori

  If I have several levels of object containment (one object defines and instantiates another object which define and instantiate another object..), is it possible to get access to upper, containing - object variables and functions, please? Example: class CObjectOne { public: CObjectOne::CObjectOne() { Create(); }; void Create(); std::vector<ObjectTwo>vObejctsTwo; int nVariableOne; } bool CObjectOne::Create() { CObjectTwo ObjectTwo(this); vObjectsTwo.push_back(ObjectTwo); } class CObjectTwo { public: CObjectTwo::CObjectTwo(CObjectOne* pObject) { pObjectOne = pObject; Create(); }; void Create(); CObjectOne* GetObjectOne(){return pObjectOne;}; std::vector<CObjectTrhee>vObjectsTrhee; CObjectOne* pObjectOne; int nVariableTwo; } bool CObjectTwo::Create() { CObjectThree ObjectThree(this); vObjectsThree.push_back(ObjectThree); } class CObjectThree { public: CObjectThree::CObjectThree(CObjectTwo* pObject) { pObjectTwo = pObject; Create(); }; void Create(); CObjectTwo* GetObjectTwo(){return pObjectTwo;}; std::vector<CObjectsFour>vObjectsFour; CObjectTwo* pObjectTwo; int nVariableThree; } bool CObjectThree::Create() { CObjectFour ObjectFour(this); vObjectsFour.push_back(ObjectFour); } main() { CObjectOne myObject1; } Say, that from within CObjectThree I need to access nVariableOne in CObjectOne. I would like to do it as follows: int nValue = vObjectThree[index].GetObjectTwo()->GetObjectOne()->nVariable1; However, after compiling and running my application, I get Memory Access Violation error. What is wrong with the code above(it is example, and might contain spelling mistakes)? Do I have to create the objects dynamically instead of statically? Is there any other way how to achieve variables stored in containing objects from withing contained objects?

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• C++ interpreter conceptual problem

  - by Jan Wilkins

  I've built an interpreter in C++ for a language created by me. One main problem in the design was that I had two different types in the language: number and string. So I have to pass around a struct like: class myInterpreterValue { myInterpreterType type; int intValue; string strValue; } Objects of this class are passed around million times a second during e.g.: a countdown loop in my language. Profiling pointed out: 85% of the performance is eaten by the allocation function of the string template. This is pretty clear to me: My interpreter has bad design and doesn't use pointers enough. Yet, I don't have an option: I can't use pointers in most cases as I just have to make copies. How to do something against this? Is a class like this a better idea? vector<string> strTable; vector<int> intTable; class myInterpreterValue { myInterpreterType type; int locationInTable; } So the class only knows what type it represents and the position in the table This however again has disadvantages: I'd have to add temporary values to the string/int vector table and then remove them again, this would eat a lot of performance again. Help, how do interpreters of languages like Python or Ruby do that? They somehow need a struct that represents a value in the language like something that can either be int or string.

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• C++ iterators, default initialization and what to use as an uninitialized sentinel.

  - by Hassan Syed

  The Context I have a custom template container class put together from a map and vector. The map resolves a string to an ordinal, and the vector resolves an ordinal (only an initial string to ordinal lookup is done, future references are to the vector) to the entry. The entries are modified intrusively to contain a a bool "assigned" and an iterator_type which is a const_iterator to the container class's map. My container class will use RCF's serialization code (which models boost::serialization) to serialize my container classes to nodes in a network. Serializing iterator's is not possible, or a can of worms, and I can easily regenerate them onces the vectors and maps are serialized on the remote site. The Question I need to default initialize, and be able to test that the iterator has not been assigned to (if it is assigned it is valid, if not it is invalid). Since map iterators are not invalidated upon operations performed on it (unless of course items are removed :D) am I to assume that map<x,y>::end() is a valid sentinel (regardless of the state of the map -- i.e., it could be empty) to initialize to ? I will always have access to the parent map, I'm just unsure wheather end() is the same as the map contents change. I don't want to use another level of indirection (--i.e., boost::optional) to achieve my goal, I'd rather forego compiler checks to correct logic, but it would be nice if I didn't need to. Misc This question exists, but most of its content seems non-sense. Assigning a NULL to an iterator is invalid according to g++ and clang++. This is another similar question, but it focuses on the common use-cases of iterators, which generally tends to be using the iterator to iterate, ofcourse in this use-case the state of the container isn't meant to change whilst iteration is going on.

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