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• A quick design question about C++ container classes in shared memory

  - by recipriversexclusion

  I am writing a simple wrapper around boost::interprocess's vector container to implement a ring buffer in shared memory (shm) for IPC. Assume that buf is an instance of RingBuffer created in shm. Now, in its ctor, buf itself allocates a private boost::interprocess::vector data member to store values, e.g. m_data. My question is: I think m_data should also be created in shared memory. But it this a necessity? What happens if buf that was created in shm itself, allocates standard memory, i.e. using new. Does this get allocated on the calling process's heap? I don't think buf is allocated there so how come a data member that is private to an object not on a process's heap gets allocated there. I'm confused.

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• Using a type parameter and a pointer to the same type parameter in a function template

  - by Darel

  Hello, I've written a template function to determine the median of any vector or array of any type that can be sorted with sort. The function and a small test program are below: #include <algorithm> #include <vector> #include <iostream> using namespace::std; template <class T, class X> void median(T vec, size_t size, X& ret) { sort(vec, vec + size); size_t mid = size/2; ret = size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } int main() { vector<double> v; v.push_back(2); v.push_back(8); v.push_back(7); v.push_back(4); v.push_back(9); double a[5] = {2, 8, 7, 4, 9}; double r; median(v.begin(), v.size(), r); cout << r << endl; median(a, 5, r); cout << r << endl; return 0; } As you can see, the median function takes a pointer as an argument, T vec. Also in the argument list is a reference variable X ret, which is modified by the function to store the computed median value. However I don't find this a very elegant solution. T vec will always be a pointer to the same type as X ret. My initial attempts to write median had a header like this: template<class T> T median(T *vec, size_t size) { sort(vec, vec + size); size_t mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } I also tried: template<class T, class X> X median(T vec, size_t size) { sort(vec, vec + size); size_t mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } I couldn't get either of these to work. My question is, can anyone show me a working implementation of either of my alternatives? Thanks for looking!

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• How can I get this code involving unique_ptr to compile?!

  - by Neil G

  #include <vector> #include <memory> using namespace std; class A { public: A(): i(new int) {} A(A const& a) = delete; A(A &&a): i(move(a.i)) {} unique_ptr<int> i; }; class AGroup { public: void AddA(A &&a) { a_.emplace_back(move(a)); } vector<A> a_; }; int main() { AGroup ag; ag.AddA(A()); return 0; } does not compile... (says that unique_ptr's copy constructor is deleted) I tried replacing move with forward. Not sure if I did it right, but it didn't work for me.

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• read file in C++

  - by Amm Sokun

  I am trying to read a list of words from a file in C++. However, the last word is read twice. I cannot understand why it is so. Can someone help me out? int main () { ifstream fin, finn; vector<string> vin; vector<string> typo; string word; fin.open("F:\\coursework\\pz\\gattaca\\breathanalyzer\\file.in"); if (!fin.is_open()) cout<<"Not open\n"; while (fin) { fin >> word; cout<<word<<endl; vin.push_back(word); } fin.close(); }

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• iPhone – How to import/drawing UI graphic elements? CGContextDrawPDFPage?

  - by Ross

  Hello, What is the best way to use the custom UI graphics on the iPhone? I've come across CGContextDrawPDFPage and Panic's Shrinkit. Should I be using storing my vector ui graphics as PDF's and loading them using CGContextDrawPDFPage to draw them. I did previously asked what way Apple store their UI graphics and was answered crushed png. The options as I see it, but I would really want to know what technique other people use. This question is for vector graphics only. Looking for what is standard / most effective / most efficient. PNG (bitmapped image) Custom UIView drawing code (generated from Opacity) PDF (I've not used this method, is it with CGContextDrawPDFPage?) Many thanks Ross

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• Matlab (matrix concatenating)

  - by jimbo

  For an mxm (square) array, how do you concatenate all the rows into a column vector with size m^2 ?

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• Multidimensional vectors in scheme?

  - by incrediman

  I earlier asked a question about arrays in scheme (turns out they're called vectors but are basically otherwise the same as you'd expect). Is there an easy way to do multidimensional arrays vectors in PLT Scheme though? For my purposes I'd like to have a procedure called make-multid-vector or something. By the way if this doesn't already exist, I don't need a full code example of how to implement it. If I have to roll this myself I'd appreciate some general direction though. The way I'd probably do it is to just iterate through each element of the currently highest dimension of the vector to add another dimension, but I can see that being a bit ugly using scheme's recursive setup. Also, this seems like something I should have been able to find myself so please know that I did actually google it and nothing came up.

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• Load binary file using fstream

  - by Kirill V. Lyadvinsky

  I'm trying to load binary file using fstream in the following way: #include <iostream #include <fstream #include <iterator #include <vector using namespace std; int main() { basic_fstream<uint32_t file( "somefile.dat", ios::in|ios::binary ); vector<uint32_t buffer; buffer.assign( istream_iterator<uint32_t, uint32_t( file ), istream_iterator<uint32_t, uint32_t() ); cout << buffer.size() << endl; return 0; } But it doesn't work. In Ubuntu it crashed with std::bad_cast exception. In MSVC++ 2008 it just prints 0. I know that I could use file.read to load file, but I want to use iterator and operator>> to load parts of the file. Is that possible? Why the code above doesn't work?

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• c++ casting base class to derived class mess

  - by alan2here

  If I were to create a base class called base and derived classes called derived_1, derived_2 etc... I use a collection of instances of the base class, then when I retrieved an element and tried to use it I would find that C++ thinks it's type is that of the base class, probably because I retrieved it from a std::vector of base. Which is a problem when I want to use features that only exist for the specific derived class who's type I knew this object was when I put it into the vector. So I cast the element into the type it is supposed to be and found this wouldn't work. (derived_3)obj_to_be_fixed; And remembered that it's a pointer thing. After some tweaking this now worked. *((derived_3*)&obj_to_be_fixed); Is this right or is there for example an abc_cast() function that does it with less mess?

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• How to Serialize a WPF Drawing?

  - by Néstor Sánchez A.

  Hi, maybe I'm missing something. I believed that WPF vector-based Drawings (like DrawingGroup, DrawingGeometry, etc.) were ready to be serialized. But they are not. So, should I navigate all these drawing childrens, and store they points, lines, brushes (that also are not serializable) and so on, and then made my custom serialization? Is really that difficult or I'm missing something pretty obvious? I mean, even serializing Bitmap images is easy. I thinked serializing vector-based drawings were easier (no quality loss, just descriptive info, no massive data). Thanks for your practical answers, alternate-way suggestions and comments!

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• Most efficient way to solve system of equations involving the digamma function?

  - by Neil G

  What is the most efficient way to solve system of equations involving the digamma function? I have a vector v and I want to solve for a vector w such that for all i: digamma(sum(w)) - digamma(w_i) = v_i and w_i 0 I found the gsl function gsl_sf_psi, which is the digamma function. Is there an identity I can use to reduce the equations? Is my best bet to use a solver? I am using C++0x; which solver is easiest to use and fast?

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• What is the most efficient way to solve system of equations containing the digamma function?

  - by Neil G

  What is the most efficient way to solve system of equations involving the digamma function? I have a vector v and I want to solve for a vector w such that for all i: digamma(sum(w)) - digamma(w_i) = v_i and w_i 0 I found the gsl function gsl_sf_psi, which is the digamma function (calculated using some kind of series.) Is there an identity I can use to reduce the equations? Is my best bet to use a solver? I am using C++0x; which solver is easiest to use and fast?

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• Adding JTextField to a JPanel and showing them

  - by Davide Gualano

  I'm building a little app using Java and Swing in NetBeans. Using NetBeans design window, I created a JFrame with a JPanel inside. Now I want to dynamically add some jTextFields to the JPanel. I wrote something like that: Vector textFieldsVector = new Vector(); JTextField tf; int i = 0; while (i < 3) { tf = new JTextField(); textFieldVector.add(tf); myPanel.add(tf); //myPanel is the JPanel where I want to put the JTextFields i++; } myPanel.validate(); myPanel.repaint(); But nothing happens: when I run the app, the JFrame shows with the JPanel inside, but the JTextFields don't. I'm a total newbie in writing graphical Java apps, so I'm surely missing something very simple, but I can't see what.

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• G++, compiler warnings, c++ templates

  - by Ian

  During the compilatiion of the C++ program those warnings appeared: c:/MinGW/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bc:/MinGW/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_algo.h:2317: instantiated from `void std::partial_sort(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Object<double>**, std::vector<Object<double>*, std::allocator<Object<double>*> > >, _Compare = sortObjects<double>]' c:/MinGW/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_algo.h:2506: instantiated from `void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Object<double>**, std::vector<Object<double>*, std::allocator<Object<double>*> > >, _Size = int, _Compare = sortObjects<double>]' c:/MinGW/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_algo.h:2589: instantiated from `void std::sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Object<double>**, std::vector<Object<double>*, std::allocator<Object<double>*> > >, _Compare = sortObjects<double>]' io/../structures/objects/../../algorithm/analysis/../../structures/list/ObjectsList.hpp:141: instantiated from `void ObjectsList <T>::sortObjects(unsigned int, T, T, T, T, unsigned int) [with T = double]' I do not why, because all objects have only template parameter T, their local variables are also T. The only place, where I am using double is main. There are objects of type double creating and adding into the ObjectsList... Object <double> o1; ObjectsList <double> olist; olist.push_back(o1); .... T xmin = ..., ymin = ..., xmax = ..., ymax = ...; unsigned int n = ...; olist.sortAllObjects(xmin, ymin, xmax, ymax, n); and comparator template <class T> class sortObjects { private: unsigned int n; T xmin, ymin, xmax, ymax; public: sortObjects ( const T xmin_, const T ymin_, const T xmax_, const T ymax_, const int n_ ) : xmin ( xmin_ ), ymin ( ymin_ ), xmax ( xmax_ ), ymax ( ymax_ ), n ( n_ ) {} bool operator() ( const Object <T> *o1, const Object <T> *o2 ) const { T dmax = (std::max) ( xmax - xmin, ymax - ymin ); T x_max = ( xmax - xmin ) / dmax; T y_max = ( ymax - ymin ) / dmax; ... return ....; } representing ObjectsList method: template <class T> void ObjectsList <T> ::sortAllObjects ( const T xmin, const T ymin, const T xmax, const T ymax, const unsigned int n ) { std::sort ( objects.begin(), objects.end(), sortObjects <T> ( xmin, ymin, xmax, ymax, n ) ); }

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• Adding an overlay to Google maps with path taken

  - by user341652

  Hi, I am trying to write a class to track a person's location(s), and to draw the path they've taken on a MapView. This feature of the program is for the user to track their speed, distance, path, etc. while running/cycling (or whatever else) using their Android phone. This is my first Android application, and I am not sure how to do the Overlay object for the MapView. I also wanted to see if anyone had opinions on the GPS-Tracking part I have written (if it would work, if there is a better way of doing it, code examples would be helpful). I currently have this for my GPSTrackerService: package org.drexel.itrain.logic; import java.util.Vector; import org.drexel.itrain.Constants; import android.app.Notification; import android.app.NotificationManager; import android.app.Service; import android.content.Context; import android.content.Intent; import android.content.SharedPreferences; import android.location.GpsSatellite; import android.location.GpsStatus; import android.location.Location; import android.location.LocationListener; import android.location.LocationManager; import android.location.GpsStatus.Listener; import android.os.Binder; import android.os.Bundle; import android.os.IBinder; import android.preference.PreferenceManager; public class GPSTrackingService extends Service { private static final int MAX_REASONABLE_SPEED = 60; private static final String TAG = "OGT.TrackingService"; private Context mContext; private LocationManager mLocationManager; private NotificationManager mNotificationManager; private Notification mNotification; private int mSatellites = 0; private int mTrackingState = Constants.GPS_TRACKING_UNKNOWN; private float mCurrentSpeed = 0; private float mTotalDistance = 0; private Location mPreviousLocation; private Vector<Location> mTrackedLocations; private LocationListener mLocationListener = null; private Listener mStatusListener = null; private IBinder binder = null; @Override public void onCreate() { super.onCreate(); this.mContext = getApplicationContext(); this.mLocationManager = (LocationManager) this.mContext.getSystemService( Context.LOCATION_SERVICE ); this.mNotificationManager = (NotificationManager) this.mContext.getSystemService( Context.NOTIFICATION_SERVICE ); this.mTrackedLocations = new Vector<Location>(); this.binder = new Binder(); SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this.mContext); binder = new Binder(); if(mTrackingState != Constants.GPS_TRACKING_UNKNOWN) { createListeners(); } } @Override public void onDestroy() { destroyListeneres(); } @Override public IBinder onBind(Intent intent) { return binder; } @Override public boolean onUnbind(Intent intent) { return true; } public boolean acceptLocation(Location proposedLocation) { if(!(proposedLocation.hasSpeed() || proposedLocation.hasAccuracy())) { return false; } else if(proposedLocation.getSpeed() >= MAX_REASONABLE_SPEED) { return false; } return true; } public void updateNotification() { //TODO Alert that no GPS sattelites are available (or are available) } public void startTracking() { this.mTrackingState = Constants.GPS_TRACKING_STARTED; this.mTotalDistance = 0; this.mCurrentSpeed = 0; this.mTrackedLocations = new Vector<Location>(); this.mPreviousLocation = null; createListeners(); } public void pauseTracking() { this.mTrackingState = Constants.GPS_TRACKING_PAUSED; this.mPreviousLocation = null; this.mCurrentSpeed = 0; } public void resumeTracking() { if(this.mTrackingState == Constants.GPS_TRACKING_STOPPED){ this.startTracking(); } this.mTrackingState = Constants.GPS_TRACKING_STARTED; } public void stopTracking() { this.mTrackingState = Constants.GPS_TRACKING_STOPPED; destroyListeneres(); } private void createListeners() { /** * LocationListener receives locations from */ this.mLocationListener = new LocationListener() { @Override public void onStatusChanged(String provider, int status, Bundle extras) { // TODO Auto-generated method stub } @Override public void onProviderEnabled(String provider) { // TODO Auto-generated method stub } @Override public void onProviderDisabled(String provider) { // TODO Auto-generated method stub } @Override public void onLocationChanged(Location location) { if(mTrackingState == Constants.GPS_TRACKING_STARTED && acceptLocation(location)) { if(mPreviousLocation != null) { //Add the distance between the new location and the previous location mTotalDistance += mPreviousLocation.distanceTo(location); } if(location.hasSpeed()) { mCurrentSpeed = location.getSpeed(); } else { mCurrentSpeed = -1; //-1 means speed N/A } mPreviousLocation = location; mTrackedLocations.add(location); } } }; /** * Receives updates reguarding the GPS Status */ this.mStatusListener = new GpsStatus.Listener() { @Override public synchronized void onGpsStatusChanged(int event) { switch( event ) { case GpsStatus.GPS_EVENT_SATELLITE_STATUS: { GpsStatus status = mLocationManager.getGpsStatus( null ); mSatellites = 0; Iterable<GpsSatellite> list = status.getSatellites(); for( GpsSatellite satellite : list ) { if( satellite.usedInFix() ) { mSatellites++; } } updateNotification(); break; } default: break; } } }; } /** * Destroys the LocationListenere and the GPSStatusListener */ private void destroyListeneres() { this.mLocationListener = null; this.mStatusListener = null; } /** * Gets the total distance traveled by the * * @return the total distance traveled (in meters) */ public float getDistance() { return mTotalDistance; } /** * Gets the current speed of the last good location * * @return the current speed (in meters/second) */ public float getSpeed() { return mCurrentSpeed; } } Any assistance would be much appreciated. This is my group's first Android app, and we are a little pressed for time at the moment. The project is for a class, and is available from SourceForge (currently called iTrain, soon to be renamed). Thanks in Advance, Steve

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• String.substring(index) has stoped my thread in debug mode.

  - by Arkaha

  Hello! I work with j2me polish 2.0.7, in eclipse 3.4.2, with wtk2.5.2_01. I create control which draws text: normal, bold, and italic. The code below is parsing raw text, and search for * and _ symbols, if found than add to draw vector the text and the drawer, and it's just stops after getting second time to the line 58: String test = new String(raw_text_buff.substring(iter)); it stops in raw_text_buff.substring(iter), ONLY in debug mode.. raw text is: bla bla bla *1000* bla bla Full code: private String raw_text = "bla bla bla *1000* bla bla"; Vector draw_items = null; private void prepareText() { char open_char = 0; int open_pos = 0; Object []param = null; StringBuffer sb = new StringBuffer(); String raw_text_buff = new String(raw_text); int iter = 0; boolean was_reset = false; while(true) { char c = raw_text_buff.charAt(iter); if(iter == raw_text_buff.length() || c == '*' || c == '_') { if(sb.length() > 0) { BmFont viewer = null; String str = sb.toString(); if(open_char == '*' && null != bm_strong) { viewer = bm_strong.getViewer(str); }else if(open_char == '_' && null != bm_italic) { viewer = bm_italic.getViewer(str); }else if(null != bm_normal) { viewer = bm_normal.getViewer(str); }else { } param = new Object[2]; param[0] = str; param[1] = viewer; if(null == draw_items) draw_items = new Vector(); draw_items.addElement(param); sb = new StringBuffer(); if(open_char == 0 && (c == '*' || c=='_')) open_char = c; else open_char = 0; String test = new String(raw_text_buff.substring(iter)); // stucks here. raw_text_buff = test; iter = 0; was_reset = true; }else { open_char = c; } if(iter == raw_text_buff.length()) break; }else { sb.append(c); } ++iter; } } What I'm doing wrong?

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• compare function for upper_bound / lower_bound

  - by Martin Beckett

  I want to find the first item in a sorted vector that has a field less than some value x. I need to supply a compare function that compares 'x' with the internal value in MyClass but I can't work out the function declaration. Can't I simply overload '<' but how do I do this when the args are '&MyClass' and 'float' ? float x; std::vector< MyClass >::iterator last = std::upper_bound(myClass.begin(),myClass.end(),x);

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• Vectors of Pointers, inheritance

  - by user308553

  Hi I am a C++ beginner just encountered a problem I don't know how to fix I have two class, this is the header file: class A { public: int i; A(int a); }; class B: public A { public: string str; B(int a, string b); }; then I want to create a vector in main which store either class A or class B vector<A*> vec; A objectOne(1); B objectTwo(2, "hi"); vec.push_back(&objectOne); vec.push_back(&objectTwo); cout << vec.at(1)->i; //this is fine cout << vec.at(1)->str; //ERROR here I am really confused, I checked sites and stuff but I just don't know how to fix it, please help thanks in advance

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• c++ quick sort running time

  - by chnet

  I have a question about quick sort algorithm. I implement quick sort algorithm and play it. The elements in initial unsorted array are random numbers chosen from certain range. I find the range of random number effects the running time. For example, the running time for 1, 000, 000 random number chosen from the range (1 - 2000) takes 40 seconds. While it takes 9 seconds if the 1,000,000 number chosen from the range (1 - 10,000). But I do not know how to explain it. In class, we talk about the pivot value can effect the depth of recursion tree. For my implementation, the last value of the array is chosen as pivot value. I do not use randomized scheme to select pivot value. int partition( vector<int> &vec, int p, int r) { int x = vec[r]; int i = (p-1); int j = p; while(1) { if (vec[j] <= x){ i = (i+1); int temp = vec[j]; vec[j] = vec[i]; vec[i] = temp; } j=j+1; if (j==r) break; } int temp = vec[i+1]; vec[i+1] = vec[r]; vec[r] = temp; return i+1; } void quicksort ( vector<int> &vec, int p, int r) { if (p<r){ int q = partition(vec, p, r); quicksort(vec, p, q-1); quicksort(vec, q+1, r); } } void random_generator(int num, int * array) { srand((unsigned)time(0)); int random_integer; for(int index=0; index< num; index++){ random_integer = (rand()%10000)+1; *(array+index) = random_integer; } } int main() { int array_size = 1000000; int input_array[array_size]; random_generator(array_size, input_array); vector<int> vec(input_array, input_array+array_size); clock_t t1, t2; t1 = clock(); quicksort(vec, 0, (array_size - 1)); // call quick sort int length = vec.size(); t2 = clock(); float diff = ((float)t2 - (float)t1); cout << diff << endl; cout << diff/CLOCKS_PER_SEC <<endl; }

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• Dijkstras Algorithm exaplination java

  - by alchemey89

  Hi, I have found an implementation for dijkstras algorithm on the internet and was wondering if someone could help me understand how the code works. Many thanks private int nr_points=0; private int[][]Cost; private int []mask; private void dijkstraTSP() { if(nr_points==0)return; //algorithm=new String("Dijkstra"); nod1=new Vector(); nod2=new Vector(); weight=new Vector(); mask=new int[nr_points]; //initialise mask with zeros (mask[x]=1 means the vertex is marked as used) for(int i=0;i<nr_points;i++)mask[i]=0; //Dijkstra: int []dd=new int[nr_points]; int []pre=new int[nr_points]; int []path=new int[nr_points+1]; int init_vert=0,pos_in_path=0,new_vert=0; //initialise the vectors for(int i=0;i<nr_points;i++) { dd[i]=Cost[init_vert][i]; pre[i]=init_vert; path[i]=-1; } pre[init_vert]=0; path[0]=init_vert; pos_in_path++; mask[init_vert]=1; for(int k=0;k<nr_points-1;k++) { //find min. cost in dd for(int j=0;j<nr_points;j++) if(dd[j]!=0 && mask[j]==0){new_vert=j; break;} for(int j=0;j<nr_points;j++) if(dd[j]<dd[new_vert] && mask[j]==0 && dd[j]!=0)new_vert=j; mask[new_vert]=1; path[pos_in_path]=new_vert; pos_in_path++; for(int j=0;j<nr_points;j++) { if(mask[j]==0) { if(dd[j]>dd[new_vert]+Cost[new_vert][j]) { dd[j]=dd[new_vert]+Cost[new_vert][j]; } } } } //Close the cycle path[nr_points]=init_vert; //Save the solution in 3 vectors (for graphical purposes) for(int i=0;i<nr_points;i++) { nod1.addElement(path[i]); nod2.addElement(path[i+1]); weight.addElement(Cost[path[i]][path[i+1]]); } }

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• Find missing birth days in Apple Addressbook

  - by Felix Ogg

  I am trying to clean the holes out of my Mac address book. As a first step I want to ask all my friends for their birth day, to be able to congratulate them with cheesy Hallmark cards. I need a "group" in my address book, to mailmerge personalized messages from. This is the Applescript I came up with: tell application "Address Book" make new group with properties {name:"No Birthday"} set birthdayPeople to (get every person whose birth date is greater than date "Monday, January 1, 1900 12:00:00 AM") repeat with i from 1 to number of items in people set thePerson to item i of people if not (birthdayPeople contains thePerson) then add thePerson to group "No Birthday" end if end repeat save end tell It breaks, but from the error messages I cannot deduce what is wrong: Result: error "Can’t make «class azf4» id \"05F770BA-7492-436B-9B58-E24F494702F8:ABPerson\" of application \"Address Book\" into type vector." number -1700 from «class azf4» id "05F770BA-7492-436B-9B58-E24F494702F8:ABPerson" to vector (BTW: Did I mention this is my first AppleScript code, EVER? So, if this code can be simplified, or made more elegant, that is welcome too.)

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• flex , ai,import,flash

  - by msaif

  can i import vector graphics file *.ai file(illustrator generated) into flex3 ??

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• Unique_ptr compiler errors

  - by Godric Seer

  I am designing and entity-component system for a project, and C++ memory management is giving me a few issues. I just want to make sure my design is legitimate. So to start I have an Entity class which stores a vector of Components: class Entity { private: std::vector<std::unique_ptr<Component> > components; public: Entity() { }; void AddComponent(Component* component) { this -> components.push_back(std::unique_ptr<Component>(component)); } ~Entity(); }; Which if I am not mistaken means that when the destructor is called (even the default, compiler created one), the destructor for the Entity, will call ~components, which will call ~std::unique_ptr for each element in the vector, and lead to the destruction of each Component, which is what I want. The component class has virtual methods, but the important part is its constructor: Component::Component(Entity parent) { parent.addComponent(this) // I am not sure if this would work like I expect // Other things here } As long as passing this to the method works, this also does what I want. My confusion is in the factory. What I want to do is something along the lines of: std::shared_ptr<Entity> createEntity() { std::shared_ptr<Entity> entityPtr(new Entity()); new Component(*parent); // Initialize more, and other types of Components return entityPtr; } Now, I believe that this setup will leave the ownership of the Component in the hands of its Parent Entity, which is what I want. First a small question, do I need to pass the entity into the Component constructor by reference or pointer or something? If I understand C++, it would pass by value, which means it gets copied, and the copied entity would die at the end of the constructor. The second, and main question is that code based on this sample will not compile. The complete error is too large to print here, however I think I know somewhat of what is going on. The compiler's error says I can't delete an incomplete type. My Component class has a purely virtual destructor with an implementation: inline Component::~Component() { }; at the end of the header. However since the whole point is that Component is actually an interface. I know from here that a complete type is required for unique_ptr destruction. The question is, how do I work around this? For reference I am using gcc 4.4.6.

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• Using boost::iterator

  - by Neil G

  I wrote a sparse vector class (see #1, #2.) I would like to provide two kinds of iterators: The first set, the regular iterators, can point any element, whether set or unset. If they are read from, they return either the set value or value_type(), if they are written to, they create the element and return the lvalue reference. Thus, they are: Random Access Traversal Iterator and Readable and Writable Iterator The second set, the sparse iterators, iterate over only the set elements. Since they don't need to lazily create elements that are written to, they are: Random Access Traversal Iterator and Readable and Writable and Lvalue Iterator I also need const versions of both, which are not writable. I can fill in the blanks, but not sure how to use boost::iterator_adaptor to start out. Here's what I have so far: template<typename T> class sparse_vector { public: typedef size_t size_type; typedef T value_type; private: typedef T& true_reference; typedef const T* const_pointer; typedef sparse_vector<T> self_type; struct ElementType { ElementType(size_type i, T const& t): index(i), value(t) {} ElementType(size_type i, T&& t): index(i), value(t) {} ElementType(size_type i): index(i) {} ElementType(ElementType const&) = default; size_type index; value_type value; }; typedef vector<ElementType> array_type; public: typedef T* pointer; typedef T& reference; typedef const T& const_reference; private: size_type size_; mutable typename array_type::size_type sorted_filled_; mutable array_type data_; // lots of code for various algorithms... public: class sparse_iterator : public boost::iterator_adaptor< sparse_iterator // Derived , array_type::iterator // Base (the internal array) (this paramater does not compile! -- says expected a type, got 'std::vector::iterator'???) , boost::use_default // Value , boost::random_access_traversal_tag? // CategoryOrTraversal > class iterator_proxy { ??? }; class iterator : public boost::iterator_facade< iterator // Derived , ????? // Base , ????? // Value , boost::?????? // CategoryOrTraversal > { }; };

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• FileInputStream for a generic file System

  - by Akhil

  I have a file that contains java serialized objects like "Vector". I have stored this file over Hadoop Distributed File System(HDFS). Now I intend to read this file (using method readObject) in one of the map task. I suppose FileInputStream in = new FileInputStream("hdfs/path/to/file"); wont' work as the file is stored over HDFS. So I thought of using org.apache.hadoop.fs.FileSystem class. But Unfortunately it does not have any method that returns FileInputStream. All it has is a method that returns FSDataInputStream but I want a inputstream that can read serialized java objects like vector from a file rather than just primitive data types that FSDataInputStream would do. Please help!

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