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  • Pointing to vectors

    - by Matt Munson
    #include <iostream> #include <vector> using namespace std; int main () { vector <int> qwerty; qwerty.push_back(5); vector <int>* p = &qwerty; cout << p[0]; //error: no match for 'operator<<' in 'std::cout << * p' } I'm generally unclear on how to use pointers with vectors, so I'm pretty mystified as to why this is not working. To my mind, this should print 5 to screen.

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  • Splitting a double vector into equal parts

    - by Cosmin
    Greetings, Any input on a way to divide a std::vector into two equal parts ? I need to find the smallest possible difference between |part1 - part2|. This is how I'm doing it now, but from what you can probably tell it will yield a non-optimal split in some cases. auto mid = std::find_if(prim, ultim, [&](double temp) -> bool { if(tempsum >= sum) return true; tempsum += temp; sum -= temp; return false; }); The vector is sorted, highest to lowest, values can indeed appear twice. I'm not expecting part1 and part2 to have the same numbers of elements, but sum(part1) should be as close as possible to sum(part2) For example if we would have { 2.4, 0.12, 1.26, 0.51, 0.70 }, the best split would be { 2.4, 0.12 } and { 1.26, 0.51, 0.70 }. If it helps, I'm trying to achieve the splitting algorithm for the Shannon Fano encoding. Any input is appreciated, thanks!

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  • C++ vector of char array

    - by Stuart
    I am trying to write a program that has a vector of char arrays and am have some problems. char test [] = { 'a', 'b', 'c', 'd', 'e' }; vector<char[]> v; v.push_back(test); Sorry this has to be a char array because I need to be able to generate lists of chars as I am trying to get an output something like. a a a b a c a d a e b a b c Can anyone point me in the right direction? Thanks

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  • why Observable snapshot observer vector

    - by han14466
    In Observable's notifyObservers method, why does the coder use arrLocal = obs.toArray();? Why does not coder iterate vector directly? Thanks public void notifyObservers(Object arg) { Object[] arrLocal; synchronized (this) { /* We don't want the Observer doing callbacks into * arbitrary code while holding its own Monitor. * The code where we extract each Observable from * the Vector and store the state of the Observer * needs synchronization, but notifying observers * does not (should not). The worst result of any * potential race-condition here is that: * 1) a newly-added Observer will miss a * notification in progress * 2) a recently unregistered Observer will be * wrongly notified when it doesn't care */ if (!changed) return; arrLocal = obs.toArray(); clearChanged(); } for (int i = arrLocal.length-1; i>=0; i--) ((Observer)arrLocal[i]).update(this, arg); }

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  • Plotting a grouped 2 dimensional vector in MATLAB

    - by Hossein
    I am trying to make a plot of a 2-dimensional vector (2D Plot). But I don't want all the datapoints to have the same color on the plot. Each datapoint corresponds to a group. I want to have different colors for each group of datapoints. class=[1 3 2 5 2 5 1 3 3 4 2 2 2] says each datapoint belongs to which group X=[x1,y1;x2,y2;x3,y3;.....] the number of these datapoints are the same as the number of elements in the class vector. Now I want to plot these based on colors.

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  • C++ arrays select square number and make new vector

    - by John Smith
    I have to see which of the following from a vector is a square number then make another vector with only the square numbers For example: (4,15,6,25,7,81) the second will be (4,25,81) 4,25,81 because 2x2=4 5x5=25 and 9x9=81 I started like this: { int A[100],n,r,i; cout<<"Number of elements="; cin>>n; for(i=1;i<=n;i++) { cout<<"A["<<i<<"]="; cin>>A[i]; } for(i=1;i<=n;i++) { r=sqrt(A[i]); if(r*r==A[i]) } return 0; } but I am not really sure how to continue

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  • initialize a const array in a class initializer in C++

    - by Nathan Fellman
    I have the following class in C++: class a { const int b[2]; // other stuff follows // and here's the constructor a(void); } The question is, how do I initialize b in the initialization list, given that I can't initialize it inside the body of the function of the constructor, because b is const? This doesn't work: a::a(void) : b([2,3]) { // other initialization stuff } Edit: The case in point is when I can have different values for b for different instances, but the values are known to be constant for the lifetime of the instance.

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  • Convert bit vector (array of booleans) to an integer, and integer to bit vector, in Java.

    - by dreeves
    What's the best way to unstub the following functions? // Convert a bit-vector to an integer. int bitvec2int(boolean[] b) { [CODE HERE] } // Convert an integer x to an n-element bit-vector. boolean[] int2bitvec(int x, int n) { [CODE HERE] } Or is there a better way to do that sort of thing than passing boolean arrays around? This comes up in an Android app where we need an array of 20 booleans to persist and the easiest way to do that is to write an integer or string to the key-value store. I'll post the way we (Bee and I) wrote the above as an answer. Thanks!

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  • C++ Vector of pointers

    - by xbonez
    For my latest CS homework, I am required to create a class called Movie which holds title, director, year, rating, actors etc. Then, I am required to read a file which contains a list of this info and store it in a vector of pointers to Movies. I am not sure what the last line means. Does it mean, I read the file, create multiple Movie objects. Then make a vector of pointers where each element (pointer) points to one of those Movie objects? Do I just make two vectors - one of pointers and one of Movies and make a one-to-one mapping of the two vectors?

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  • C++ Memory allocation question involving vectors

    - by TheFuzz
    vector< int > vect; int *int_ptr = new int(10); vect.push_back( *int_ptr ); I under stand that every "new" needs to be followed by a "delete" at some point but does the clear() method clean this memory? What about this method of doing the same thing: vector< int > vect; int int_var = 10; vect.push_back( int_var ); From what I understand, clear() calls the variables destructors, but both vect.push_back() methods in this example push an object on the vector, not a pointer. so does the first example using an int pointer need something other than clear() to clean up memory?

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  • Boost ASIO read X bytes synchroniously into a vector

    - by xeross
    Hey, I've been attempting to write a client/server app with boost now, so far it sends and receives but I can't seem to just read X bytes into a vector. If I use the following code vector<uint8_t> buf; for (;;) { buf.resize(4); boost::system::error_code error; size_t len = socket.read_some(boost::asio::buffer(buf), error); if (error == boost::asio::error::eof) break; // Connection closed cleanly by peer. else if (error) throw boost::system::system_error(error); // Some other error. } And the packet is bigger then 4 bytes then it seems it keeps writing into those 4 bytes until the entire packet has been received, however I want it to fetch 4 bytes, then allow me to parse them, and then get the rest of the packet. Can anyone provide me with a working example, or at least a pointer on how to make it work properly ? Regards, Xeross

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  • How to delay static initialization within a property

    - by Mystagogue
    I've made a class that is a cross between a singleton (fifth version) and a (dependency injectable) factory. Call this a "Mono-Factory?" It works, and looks like this: public static class Context { public static BaseLogger LogObject = null; public static BaseLogger Log { get { return LogFactory.instance; } } class LogFactory { static LogFactory() { } internal static readonly BaseLogger instance = LogObject ?? new BaseLogger(null, null, null); } } //USAGE EXAMPLE: //Optional initialization, done once when the application launches... Context.LogObject = new ConLogger(); //Example invocation used throughout the rest of code... Context.Log.Write("hello", LogSeverity.Information); The idea is for the mono-factory could be expanded to handle more than one item (e.g. more than a logger). But I would have liked to have made the mono-factory look like this: public static class Context { private static BaseLogger LogObject = null; public static BaseLogger Log { get { return LogFactory.instance; } set { LogObject = value; } } class LogFactory { static LogFactory() { } internal static readonly BaseLogger instance = LogObject ?? new BaseLogger(null, null, null); } } The above does not work, because the moment the Log property is touched (by a setter invocation) it causes the code path related to the getter to be executed...which means the internal LogFactory "instance" data is always set to the BaseLogger (setting the "LogObject" is always too late!). So is there a decoration or other trick I can use that would cause the "get" path of the Log property to be lazy while the set path is being invoked?

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  • List of good Inkscape tutorial

    - by marco.ragogna
    Inkscape seems to be a great open source software to draw and create vector graphics. Now, I would like to learn more how to use it and I would like to ask you to list here good tutorials and articles that helped you in learning Inkscape. Thank you

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  • How to install Uniconverter (command-line app) on Mac OS 10.7.2 (Lion)?

    - by RecentlyAFish
    Uniconverter is a command-line tool that shares code with the sK1 Project. it's used to convert from one type of vector graphic file to another like this: uniconverter before.eps after.svg I'm looking for a step by step solution to install this tool on my laptop. A similar question posted on the Uniconverter Forum back in August is still unanswered. I read about Uniconverter in an answer posted by Neil but don't grok how to send him a message directly for more details.

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  • How does badBIOS jumps airgaps?

    - by Ash
    I was reading this article from Ars on badBIOS and came across this line which states the malware, has the ability to use high-frequency transmissions passed between computer speakers and microphones to bridge airgaps. and wondered if this attack vector was possible ? Not only me , but all other readers were wondering if this had any logical explanation.Can a computer transmit packets via high-frequency sounds broadcast over speakers ?

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  • How do I prevent a curve snapping to a straight line in Flash CS4?

    - by Kelix
    I am trying to do some vector drawing in Flash but am having trouble when "curving" lines. At the moment, unless the curve is significant, it snaps back to a straight line meaning I am finding it impossible to draw shallow curves. Any idea how to turn this snapping off? I have tried turning everything off in View Snapping and it makes no difference.

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  • Efficiency of Java "Double Brace Initialization"?

    - by Jim Ferrans
    In Hidden Features of Java the top answer mentions Double Brace Initialization, with a very enticing syntax: Set<String> flavors = new HashSet<String>() {{ add("vanilla"); add("strawberry"); add("chocolate"); add("butter pecan"); }}; This idiom creates an anonymous inner class with just an instance initializer in it, which "can use any [...] methods in the containing scope". Main question: Is this as inefficient as it sounds? Should its use be limited to one-off initializations? (And of course showing off!) Second question: The new HashSet must be the "this" used in the instance initializer ... can anyone shed light on the mechanism? Third question: Is this idiom too obscure to use in production code? Summary: Very, very nice answers, thanks everyone. On question (3), people felt the syntax should be clear (though I'd recommend an occasional comment, especially if your code will pass on to developers who may not be familiar with it). On question (1), The generated code should run quickly. The extra .class files do cause jar file clutter, and slow program startup slightly (thanks to coobird for measuring that). Thilo pointed out that garbage collection can be affected, and the memory cost for the extra loaded classes may be a factor in some cases. Question (2) turned out to be most interesting to me. If I understand the answers, what's happening in DBI is that the anonymous inner class extends the class of the object being constructed by the new operator, and hence has a "this" value referencing the instance being constructed. Very neat. Overall, DBI strikes me as something of an intellectual curiousity. Coobird and others point out you can achieve the same effect with Arrays.asList, varargs methods, Google Collections, and the proposed Java 7 Collection literals. Newer JVM languages like Scala, JRuby, and Groovy also offer concise notations for list construction, and interoperate well with Java. Given that DBI clutters up the classpath, slows down class loading a bit, and makes the code a tad more obscure, I'd probably shy away from it. However, I plan to spring this on a friend who's just gotten his SCJP and loves good natured jousts about Java semantics! ;-) Thanks everyone!

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  • List<element> initialization fires "Process is terminated due to StackOverflowException"

    - by netmajor
    I have structs like below and when I do that initialization: ArrayList nodesMatrix = null; List<vertex> vertexMatrix = null; List<bool> odwiedzone = null; List<element> priorityQueue = null; vertexMatrix = new List<vertex>(nodesNr + 1); nodesMatrix = new ArrayList(nodesNr + 1); odwiedzone = new List<bool>(nodesNr + 1); priorityQueue = new List<element>(); arr.NodesMatrix = nodesMatrix; arr.VertexMatrix = vertexMatrix; arr.Odwiedzone = odwiedzone; arr.PriorityQueue = priorityQueue; //only here i have exception debuger fires Process is terminated due to StackOverflowException :/ Some idea why this collection fires this exception ? private struct arrays { ArrayList nodesMatrix; public ArrayList NodesMatrix { get { return nodesMatrix; } set { nodesMatrix = value; } } List<vertex> vertexMatrix; public List<vertex> VertexMatrix { get { return vertexMatrix; } set { vertexMatrix = value; } } List<bool> odwiedzone; public List<bool> Odwiedzone { get { return odwiedzone; } set { odwiedzone = value; } } public List<element> PriorityQueue { get { return PriorityQueue; } set { PriorityQueue = value; } } } public struct element : IComparable { public double priority { get { return priority; } set { priority = value; } } public int node { get { return node; } set { node = value; } } public element(double _prio, int _node) { priority = _prio; node = _node; } #region IComparable Members public int CompareTo(object obj) { element elem = (element)obj; return priority.CompareTo(elem.priority); } #endregion

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  • Function-Local Static Const variable Initialization semantics.

    - by Hassan Syed
    The questions are in bold, for those that cannot be bothered reading a question in depth. This is a followup to this question. It is to do with the initialization semantics of static variables in functions. Static variables should be initialized once, and their internal state might be altered later - as I (currently) do in the linked question. However, the code in question does not require the feature to change the state of the variable later. Let me clarrify my position, since I don't require the string object's internal state to change. The code is for a trait class for meta programming, and as such would would benifit from a const char * const ptr -- thus Ideally a local cost static const variable is needed. My educated guess is that in this case the string in question will be optimally placed in memory by the link-loader, and that the code is more secure and maps to the intended semantics. This leads to the semantics of such a variable "The C++ Programming language Third Edition -- Stroustrup" does not have anything (that I could find) to say about this matter. All that is said is that the variable is initialized once when the flow of control of the thread first reaches the code. This leads me to ponder if the following code would be sensible, and if not what are the intended semantics ?. #include <iostream> const char * const GetString(const char * x_in) { static const char * const x = x_in; return x; } int main() { const char * const temp = GetString("yahoo"); std::cout << temp << std::endl; const char * const temp2 = GetString("yahoo2"); std::cout << temp2 << std::endl; } The following compiles on GCC and prints "yahoo" twice. Which is what I want -- However it might not be standards compliant (which is why I post this question). It might be more elegant to have two functions, "SetString" and "String" where the latter forwards to the first. If it is standards compliant does someone know of a templates implementation in boost (or elsewhere) ?

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  • Explicit Type Conversion and Multiple Simple Type Specifiers

    - by James McNellis
    To value initialize an object of type T, one would do something along the lines of one of the following: T x = T(); T x((T())); My question concerns types specified by a combination of simple type specifiers, e.g., unsigned int: unsigned int x = unsigned int(); unsigned int x((unsigned int())); Visual C++ 2008 and Intel C++ Compiler 11.1 accept both of these without warnings; Comeau 4.3.10.1b2 and g++ 3.4.5 (which is, admittedly, not particularly recent) do not. According to the C++ standard (C++03 5.2.3/2, expr.type.conv): The expression T(), where T is a simple-type-specifier (7.1.5.2) for a non-array complete object type or the (possibly cv-qualified) void type, creates an rvalue of the specified type, which is value-initialized 7.1.5.2 says, "the simple type specifiers are," and follows with a list that includes unsigned and int. Therefore, given that in 5.2.3/2, "simple-type-specifier" is singular, and unsigned and int are two type specifiers, are the examples above that use unsigned int invalid? (and, if so, the followup is, is it incorrect for Microsoft and Intel to support said expressions?) This question is more out of curiosity than anything else; for all of the types specified by a combination of multiple simple type specifiers, value initialization is equivalent to zero initialization. (This question was prompted by comments in response to this answer to a question about initialization).

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  • Java ME scorecard with vector and multiple input fields/screens

    - by proximity
    I have made a scorecard with 5 holes, for each a input field (shots), and a image is shown. The input should be saved into a vector and shown on each hole, eg. hole 2: enter shots, underneath it "total shots: 4" (if you have made 4 shots on hole 1). In the end I would need a sum up of all shots, eg. Hole 1: 4 Hole 2: 3 Hole 3: 2 ... Total: 17 Could someone please help me with this task? { f = new Form("Scorecard"); d = Display.getDisplay(this); mTextField = new TextField("Shots:", "", 2, TextField.NUMERIC); f.append(mTextField); mStatus = new StringItem("Hole 1:", "Par 3, 480m"); f.append(mStatus); try { Image j = Image.createImage("/hole1.png"); ImageItem ii = new ImageItem("", j, 3, "Hole 1"); f.append(ii); } catch (java.io.IOException ioe) {} catch (Exception e) {} f.addCommand(mBackCommand); f.addCommand(mNextCommand); f.addCommand(mExitCommand); f.setCommandListener(this); Display.getDisplay(this).setCurrent(f); } public void startApp() { mBackCommand = new Command("Back", Command.BACK, 0); mNextCommand = new Command("Next", Command.OK, 1); mExitCommand = new Command("Exit", Command.EXIT, 2); } public void pauseApp() { } public void destroyApp(boolean unconditional) { } public void commandAction(Command c, Displayable d) { if (c == mExitCommand) { destroyApp(true); notifyDestroyed(); } else if ( c == mNextCommand) { // -> go to next hole input! save the mTextField input into a vector. } } } ------------------------------ Full code --------------------------------- import java.util.; import javax.microedition.midlet.; import javax.microedition.lcdui.*; public class ScorerMIDlet extends MIDlet implements CommandListener { private Command mExitCommand, mBackCommand, mNextCommand; private Display d; private Form f; private TextField mTextField; private Alert a; private StringItem mHole1; private int b; // repeat holeForm for all five holes and add the input into a vector or array. Display the values in the end after asking for todays date and put todays date in top of the list. Make it possible to go back in the form, eg. hole 3 - hole 2 - hole 1 public void holeForm(int b) { f = new Form("Scorecard"); d = Display.getDisplay(this); mTextField = new TextField("Shots:", "", 2, TextField.NUMERIC); f.append(mTextField); mHole1 = new StringItem("Hole 1:", "Par 5, 480m"); f.append(mHole1); try { Image j = Image.createImage("/hole1.png"); ImageItem ii = new ImageItem("", j, 3, "Hole 1"); f.append(ii); } catch (java.io.IOException ioe) {} catch (Exception e) {} // Set date&time in the end long now = System.currentTimeMillis(); DateField df = new DateField("Playing date:", DateField.DATE_TIME); df.setDate(new Date(now)); f.append(df); f.addCommand(mBackCommand); f.addCommand(mNextCommand); f.addCommand(mExitCommand); f.setCommandListener(this); Display.getDisplay(this).setCurrent(f); } public void startApp() { mBackCommand = new Command("Back", Command.BACK, 0); mNextCommand = new Command("OK-Next", Command.OK, 1); mExitCommand = new Command("Exit", Command.EXIT, 2); b = 0; holeForm(b); } public void pauseApp() {} public void destroyApp(boolean unconditional) {} public void commandAction(Command c, Displayable d) { if (c == mExitCommand) { destroyApp(true); notifyDestroyed(); } else if ( c == mNextCommand) { holeForm(b); } } }

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  • SVG to Android Shape

    - by Buggieboy
    I have started learning about vector drawing in Android with the Shape class. Since Shape is a Drawable, and Drawables are usually defined as XML, it sounds a lot like the vector drawing commands in SVG. My question is this: Has anybody created an XSLT transformation, or other mechanism, for converting an SVG drawing description into Android Shapes?

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  • Why is there no way to resize SRFI-4 vectors in Scheme?

    - by Jay
    I see that SRFI 4 does not mention resizing of vectors. I'm using f64vectors (for which I need fast access), and I'd like to be able to resize them quickly (similar to what realloc does in C), and not necessarily copy the whole vector. Since I didn't find any references to a "resize-f64vector" procedure, I'd like to know why it doesn't exist (and if making a new vector and copying over is my only option).

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