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  • Tech Article: Tired of Null Pointer Exceptions? Use Java SE 8's Optional!

    - by Tori Wieldt
    A wise man once said you are not a real Java programmer until you've dealt with a null pointer exception. The null reference is the source of many problems because it is often used to denote the absence of a value. Java SE 8 introduces a new class called java.util.Optional that can alleviate some of these problems. In the tech article "Tired of Null Pointer Exceptions? Use Java SE 8's Optional!" Java expert Raoul-Gabriel Urma shows you how to make your code more readable and protect it against null pointer exceptions. Urma explains "The purpose of Optional is not to replace every single null reference in your codebase but rather to help design better APIs in which—just by reading the signature of a method—users can tell whether to expect an optional value. In addition, Optional forces you to actively unwrap an Optional to deal with the absence of a value; as a result, you protect your code against unintended null pointer exceptions." Learn how to go from writing painful nested null checks to writing declarative code that is composable, readable, and better protected from null pointer exceptions. Read "Tired of Null Pointer Exceptions? Use Java SE 8's Optional!"

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  • casting doubles to integers in order to gain speed

    - by antirez
    Hello all, in Redis (http://code.google.com/p/redis) there are scores associated to elements, in order to take this elements sorted. This scores are doubles, even if many users actually sort by integers (for instance unix times). When the database is saved we need to write this doubles ok disk. This is what is used currently: snprintf((char*)buf+1,sizeof(buf)-1,"%.17g",val); Additionally infinity and not-a-number conditions are checked in order to also represent this in the final database file. Unfortunately converting a double into the string representation is pretty slow. While we have a function in Redis that converts an integer into a string representation in a much faster way. So my idea was to check if a double could be casted into an integer without lost of data, and then using the function to turn the integer into a string if this is true. For this to provide a good speedup of course the test for integer "equivalence" must be fast. So I used a trick that is probably undefined behavior but that worked very well in practice. Something like that: double x = ... some value ... if (x == (double)((long long)x)) use_the_fast_integer_function((long long)x); else use_the_slow_snprintf(x); In my reasoning the double casting above converts the double into a long, and then back into an integer. If the range fits, and there is no decimal part, the number will survive the conversion and will be exactly the same as the initial number. As I wanted to make sure this will not break things in some system, I joined #c on freenode and I got a lot of insults ;) So I'm now trying here. Is there a standard way to do what I'm trying to do without going outside ANSI C? Otherwise, is the above code supposed to work in all the Posix systems that currently Redis targets? That is, archs where Linux / Mac OS X / *BSD / Solaris are running nowaday? What I can add in order to make the code saner is an explicit check for the range of the double before trying the cast at all. Thank you for any help.

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  • Windows 2008 R2 RDS - Double Login

    - by colo_joe
    Issue: Double logins when connecting to RemoteApps or Remote Desktop Environment: Gateway = 1 server 2008 R2 - Roles = Gateway, Session Broker, Connection Mgr, Session Host Configuration server Session hosts = 2 servers 2008 R2 - Roles = App Manager and Session host configuration Testing: I can get to the url http://RDS.domain.com/rdweb - I get prompted for authentication (1) Pass authentication, get list of remote apps. Click on remoteapps or remote desktop, get prompted for authentication again (2). Pass authentication, I get access to app or RDP. Done so far. On session host Signed rdp files with cert. Added the following to the custom RDP settings: Authenticaton level:i:0 = If server authentication fails, connect to the computer without warning (Connect and don’t warn me). prompt for credentials on client:i:1 = RDC will prompt for credentials when connecting to a server that does not support server authentication. enablecredsspsupport:i:1 = RDP will use CredSSP, if the operating system supports CredSSP. Edited the javascript file as found in http://support.microsoft.com/kb/977507 Added Connection ID, and added Web Access server to TS Web Access Computers group on the Session host servers, and Signed apps as found in hxxp://blogs.msdn.com/b/rds/archive/2009/08/11/introducing-web-single-sign-on-for-remoteapp-and-desktop-connections.aspx Note: This double login happens internally and externally.

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  • Create a PDF that defaults to flip on short edge when printed double-sided

    - by user568458
    We're creating a 2-page PDF brochure with a target audience who will print it on their regular office or home printers. If it is printed on a double-sided printer (common in offices), it'll come out correctly if set manually by the user to "Flip on short edge", but will come out with the second page upside down if default settings are used (flip on long edge). Our target audience aren't very tech-literate, and we've found that even within our own office network there is variation in the location of the 'Flip on short edge' setting - so it isn't realistic to give everyone who downloads the PDF instructions on how to change this setting or to expect everyone to find out how to change the setting off their own backs. So, when creating a PDF (ideally using Adobe InDesign or Acrobat, but if other software or hacking is needed that's fine...), is there a way to configure the PDF file itself so that when printed double-sided with default settings, it flips on the short edge? If possible, it'll be useful supplementary info to know how reliable any such methods are across different PDF readers (e.g. Adobe Reader, Acrobat, Mac Preview, inbuilt browser readers (e.g. chrome), FoxIt, etc). If questions about content creation like this aren't a great fit here, feel free to migrate it to the graphic design stackexchange site - this question seems to fall half way between the two sites

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  • mouse pointer moving on its own

    - by PA
    After two months of working correctly, I am experiencing an strange and very annoying problem. My mouse pointer is moving on its own. If I move the mouse to the left, as soon as I stop the movement, the pointer runs again to the far right. This makes the mouse totally unusable. The mouse device is an optical USB mouse. It is not a problem with the mouse itself. I have tried with another mouse, same problem. (both mice are OK, I have tried both mice on my laptop, both worked perfectly) Have tried different surfaces, too. Same problem. System is Windows XP Pro SP3. Computer is a desktop PC two months old. I suspected it could be a problem with the mouse driver. But both mice are from different brand, so I suppose they use different drivers. What else can I try? any suggestion?

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  • Why Garbage Collection if smart pointers are there

    - by Gulshan
    This days, so many languages are garbage collected. Even it is available for C++ by third parties. But, C++ has RAII and smart pointers. So, what's the point of using garbage collection? Is it doing something extra? And in other languages like C#, if all the references are treated as smart pointers(keeping RAII aside), by specification and by implementation, will there be still any need of garbage collectors? If no, then why this is not so?

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  • how to do partial updates in OpenGL?

    - by Will
    It is general wisdom that you redraw the entire viewport on each frame. I would like to use partial updates; what are the various ways can do that, and what are their pros, cons and relative performance? (Using textures, FBOs, the accumulator buffer, any kind of scissors that can affect swapbuffers etc?) A scenario: a scene with a fair few thousand visible trees; although the textures are mipmapped and they are drawn via VBOs roughly front-to-back with so on, its still a lot of polys. Would streaming a single screen-sized texture be better than throwing them at the screen every frame? You'd have to redraw and recapture them only on camera movement or as often as your wind model updates or whatever, which need not be every frame.

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  • Triple buffering causes input lag?

    - by user782220
    Consider some time in between two vsyncs. Suppose the first display buffer is being used to display the current image, and suppose the game was really fast and computed and rendered the next image to the second display buffer and the next one after that to the third display buffer. That is the rendering to the second and third display buffer happens so fast that it occurs before the next vsync. Suppose input from the user comes in now. What you would like is for the results of the input to show up on the next vsync or (probably more typical) the vsync after that. However, with the third display buffer already rendered the input can only effect the image after that. Meaning the input will only take effect at best 3 vsyncs later. I wish i had an image to show the exact timings of what I mean.

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  • Is using a dedicated thread just for sending gpu commands a good idea?

    - by tigrou
    The most basic game loop is like this : while(1) { update(); draw(); swapbuffers(); } This is very simple but have a problem : some drawing commands can be blocking and cpu will wait while he could do other things (like processing next update() call). Another possible solution i have in mind would be to use two threads : one for updating and preparing commands to be sent to gpu, and one for sending these commands to the gpu : //first thread while(1) { update(); render(); // use gamestate to generate all needed triangles and commands for gpu // put them in a buffer, no command is send to gpu // two buffers will be used, see below pulse(); //signal the other thread data is ready } //second thread while(1) { wait(); // wait for second thread for data to come send_data_togpu(); // send prepared commands from buffer to graphic card swapbuffers(); } also : two buffers would be used, so one buffer could be filled with gpu commands while the other would be processed by gpu. Do you thing such a solution would be effective ? What would be advantages and disadvantages of such a solution (especially against a simpler solution (eg : single threaded with triple buffering enabled) ?

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  • Implementing a list with unique_ptr<>? [migrated]

    - by Alexander Duchene
    As I understand it, a unique_ptr signifies exclusive ownership. A singly linked list seems to fit this, with each node owning the next, like (pseduocode alert) class node{ public: unique_ptr<node> next; int value; }; but I don't understand how to perform operations like traversing the list, where I'm used to doing here=here->next; How do you implement data structures using unique_ptr's? Are they the right tool for the job?

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  • Administrator's shortcut to batch file with double quoted parameters

    - by XXB
    Take an excruciatingly simple batch file: echo hi pause Save that as test.bat. Now, make a shortcut to test.bat. The shortcut runs the batch file, which prints "hi" and then waits for a keypress as expected. Now, add some argument to the target of the shortcut. Now you have a shortcut to: %path%\test.bat some args The shortcut runs the batch file as before. Now, run the shortcut as administrator. (This is on Windows 7 by the way.) You can use either right-click - Run as Administrator, or go to the shortcut's properties and check the box in the advanced section. Tell UAC that it's okay and once again the shortcut runs the batch file as expected. Now, change the arguments in the target of the shortcut to add double quotes: %path%\test.bat "some args" Now try the shortcut as administrator. It doesn't work this time! A command window pops up and and disappears too fast to see any error. I tried adding test.log 2&1 to the shortcut, but no log is created in this case. Try running the same shortcut (with the double quotes) but not as Administrator. It runs the batch file fine. So, it seems the behavior is not because of the double quoted parameters, and it's not because it's run as Administrator. It's some weird combination of the two. I also tried running the same command from an administrator's command window. This ran the batch file as expected without error. Running the shortcut from the command window spawned a new command window which flashed and went away. So apparently the issue is caused by a combination of administrator, the shortcut, and the double quotes. I'm totally stumped, does anyone have any idea what's going on?

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  • Fixed mouse pointer with jQuery draggable

    - by MikeWyatt
    I'm building a little game in HTML5. The canvas element is a viewport into the game world. The user can move the viewport's position in the world by clicking and dragging with the mouse on a small icon. The problem is that the scrolling stops when the mouse pointer hits the edge of the screen. In all likelihood, that will limit scrolling in one of the directions severely, since the icon will be in one of the corners of the page. The only technical solution I can think of would be to somehow fix the mouse pointer's position on the icon and detect the relative movement each frame. Basically I would just reset the pointer position back to the center of the icon after each drag event. Unfortunately, I'm fairly positive that this is not possible. Playing with the user's pointer is a big no-no from a usability and security standpoint. So, is there any other way to do what I want? I'm primarily looking for technical ideas here, but suggestions for a more appropriate interface would also be welcome.

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  • Listen to double click not click

    - by Mohsen
    I'm just wondering why click event happening when I dbclick an element? I have this code:(JSBIN) HTML <p id="hello">Hello World</p> JavaScript document.getElementById('hello').addEventListener('click', function(e){ e.preventDefault(); this.style.background = 'red'; }, false); document.getElementById('hello').addEventListener('dbclick', function(){ this.style.background = 'yellow'; }, false); It should do different things for click and double click, but it seems when you double click on the p it catch click event in advance and ignore double click. I tried preventDefault the click event too. How can I listen to just dbclick? UPDATE I had a typo in my code. dbclick is wrong. It's dblclick. Anyway the problem still exist. When user double clicks the click event happens. This is updated code that prove it:(JSBin) document.getElementById('hello').addEventListener('click', function(e){ e.preventDefault(); this.style.background = 'red'; this.innerText = "Hello World clicked"; }, false); document.getElementById('hello').addEventListener('dblclick', function(){ this.style.background = 'green'; }, false);

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  • How to treat Base* pointer as Derived<T>* pointer?

    - by dehmann
    I would like to store pointers to a Base class in a vector, but then use them as function arguments where they act as a specific class, see here: #include <iostream> #include <vector> class Base {}; template<class T> class Derived : public Base {}; void Foo(Derived<int>* d) { std::cerr << "Processing int" << std::endl; } void Foo(Derived<double>* d) { std::cerr << "Processing double" << std::endl; } int main() { std::vector<Base*> vec; vec.push_back(new Derived<int>()); vec.push_back(new Derived<double>()); Foo(vec[0]); Foo(vec[1]); delete vec[0]; delete vec[1]; return 0; } This doesn't compile: error: call of overloaded 'Foo(Base*&)' is ambiguous Is it possible to make it work? I need to process the elements of the vector differently, according to their int, double, etc. types.

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  • Perl regex which grabs ALL double letter occurances in a line

    - by phileas fogg
    Hi all, still plugging away at teaching myself Perl. I'm trying to write some code that will count the lines of a file that contain double letters and then place parentheses around those double letters. Now what I've come up with will find the first ocurrance of double letters, but not any other ones. For instance, if the line is: Amp, James Watt, Bob Transformer, etc. These pioneers conducted many My code will render this: 19 Amp, James Wa(tt), Bob Transformer, etc. These pioneers conducted many The "19" is the count (of lines containing double letters) and it gets the "tt" of "Watt" but misses the "ee" in "pioneers". Below is my code: $file = '/path/to/file/electricity.txt'; open(FH, $file) || die "Cannot open the file\n"; my $counter=0; while (<FH>) { chomp(); if (/(\w)\1/) { $counter += 1; s/$&/\($&\)/g; print "\n\n$counter $_\n\n"; } else { print "$_\n"; } } close(FH); What am I overlooking? TIA!

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  • A Question about dereferencing pointer to incomplete type In C programming

    - by user552279
    Hi, can you explain this error for me? Blockquote /////////////////////////////// In my A.h file: struct TreeNode; struct TreeHead; typedef struct TreeNode * Node; typedef struct TreeHead * Head; /////////////////////////////// In my A.c file: struct TreeNode { char* theData; Node Left; Node Right; } ; struct TreeHead{ int counter; char type; Node Root; }; Head Initialisation() { Head treeHead; treeHead = malloc(sizeof (struct TreeHead)); treeHead-Root = malloc(sizeof (struct TreeNode)); return treeHead; } /////////////////////////////// In my Main.c file: Head head; Node tree; int choose =5; head = Initialisation(); (head-Root) = tree; //When compiling, this line has an error: error: dereferencing pointer to incomplete type Blockquote haed-Root will return a Node pointer, tree is also a Node pointer. So why error is dereferencing pointer to "incomplete" type?

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  • Utility for scanning stacks of double-sided documents

    - by Peter Becich
    I have a simplex scanner with document feeder, and am looking for the best way to scan double-sided notes. It would be useful to be able to scan the same stack twice, once flipped, and have a utility automatically interleave the scanned images. Multi-page PDF export would also be nice. Is there a tool to do this? Otherwise, I'm considering writing it in Python, with the imagescanner module, if it can use the ADF -- http://pypi.python.org/pypi/imagescanner/0.9 Thanks

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  • Direct Link to IRC Server with Double ##

    - by bemental
    Trying to create a direct link to an IRC channel with double octothorpes (##). Freenode policy dictates off-topic channels require ## before the channel name. This O'Reilly 'hack' post gives solid instructions for how to link to a channel and open in the default client on a system, but no guidance for channels with doubles. Links to single channels are formatted as "irc://irc-server:port/channel?key"

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