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  • I just don't get the C++ Pointer/Reference system.

    - by gnm
    I've never had problems with references as in Python (implicit) or PHP (explicit &). In PHP you write $p = &$myvar; and you have $p as a reference pointing to $myVar. So I know in C++ you can do this: void setToSomething( int& var ) { var = 123; } int myInt; setToSomething( myInt ); Myint is now 123, why? Doesn't & mean "memory address of" x in C++? What do I do then if var is only the adress to myInt and not a pointer? void setToSomething( int* var ) { var* = 123; } int myInt; int* myIntPtr = &myInt; setToSomething( myIntPtr ); Does the above work as expected? I don't understand the difference between * and & in C++ fully. They tell you & is used to get the adress of a variable, but why IN GODS NAME does that help you in functions etc. like in the first example?

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  • How to find the largest power of 2 less than the given number

    - by nazar_art
    I need to find the largest power of 2 less than the given number. And I stuck and can't find any solution. Code: public class MathPow { public int largestPowerOf2 (int n) { int res = 2; while (res < n) { res =(int)Math.pow(res, 2); } return res; } } This doesn't work correctly. Testing output: Arguments Actual Expected ------------------------- 9 16 8 100 256 64 1000 65536 512 64 256 32 How to solve this issue?

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  • Performance implications of using a variable versus a magic number

    - by Nathan
    I'm often confused by this. I've always been taught to name numbers I use often using variables or constants, but if it reduces the efficiency of the program, should I still do it? Heres an example: private int CenterText(Font font, PrintPageEventArgs e, string text) { int recieptCenter = 125; int stringLength = Convert.ToInt32(e.Graphics.MeasureString(text, font)); return recieptCenter - stringLength / 2; } The above code is using named variables, but runs slower then this code: private int CenterText(Font font, PrintPageEventArgs e, string text) { return 125 - Convert.ToInt32(e.Graphics.MeasureString(text, font) / 2); } In this example, the difference in execution time is minimal, but what about in larger blocks of code?

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  • mysql codeigniter active record m:m deletion

    - by sea_1987
    Hi There, I have a table 2 tables that have a m:m relationship, what I can wanting is that when I delete a row from one of the tables I want the row in the joining table to be deleted as well, my sql is as follow, Table 1 CREATE TABLE IF NOT EXISTS `job_feed` ( `id` int(11) NOT NULL AUTO_INCREMENT, `body` text NOT NULL, `date_posted` int(10) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; Table 2 CREATE TABLE IF NOT EXISTS `job_feed_has_employer_details` ( `job_feed_id` int(11) NOT NULL, `employer_details_id` int(11) NOT NULL, PRIMARY KEY (`job_feed_id`,`employer_details_id`), KEY `fk_job_feed_has_employer_details_job_feed1` (`job_feed_id`), KEY `fk_job_feed_has_employer_details_employer_details1` (`employer_details_id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; So what I am wanting to do is, if the a row is deleted from table1 and has an id of 1 I want the row in table to that also has that idea as part of the relationship also. I want to do this in keeping with codeigniters active record class I currently have this, public function deleteJobFeed($feed_id) { $this->db->where('id', $feed_id) ->delete('job_feed'); return $feed_id; }

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  • Writing a C++ wrapper for a C library

    - by stripes
    I have a legacy C library, written in an OO type form. Typical functions are like: LIB *lib_new(); void lib_free(LIB *lib); int lib_add_option(LIB *lib, int flags); void lib_change_name(LIB *lib, char *name); I'd like to use this library in my C++ program, so I'm thinking a C++ wrapper is required. The above would all seem to map to something like: class LIB { public: LIB(); ~LIB(); int add_option(int flags); void change_name(char *name); ... }; I've never written a C++ wrapper round C before, and can't find much advice about it. Is this a good/typical/sensible approach to creating a C++/C wrapper?

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  • Some questions about focus on WPF

    - by ThitoO
    Hello, I've a little problem about focus on WPF. I whant to create a window, always on top, and that never get the focus (even if we click on it). Here's my solution : public partial class SkinWindow : Window { public SkinWindow() { InitializeComponent(); Loaded += ( object sender, RoutedEventArgs e ) => SetNoActiveWindow(); } private void SetNoActiveWindow() { WindowInteropHelper helper = new WindowInteropHelper( this ); SetWindowLong( helper.Handle, GWL_EXSTYLE, WS_EX_NOACTIVATE ); LockSetForegroundWindow( LSFW_LOCK ); } const int GWL_EXSTYLE = -20; const int WS_EX_NOACTIVATE = 134217728; const int LSFW_LOCK = 1; [DllImport( "user32" )] public static extern bool LockSetForegroundWindow( uint UINT ); [DllImport( "user32" )] public static extern IntPtr SetWindowLong( IntPtr hWnd, int nIndex, int dwNewLong ); } First problem : It's works, but I've to select an other window to "remove" the focus of my application (after the focus is not gave again, even if I click on my window). Second problem : When I move or resize the window, the modifications happens when I drop the window. Do you have any ideas / links / docs ? Thank you :)

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  • pointers for getting elements of an array in C

    - by Manolo
    I am a newbie in C and I would like to get the elements of an array with a function, I have tried different options, but I still do not get the elements. My function is: void getelements(int *a, int cl) { int *p; for (p=&a[0];p<&a[cl];p++) { printf("%d\n",*p); } } I know that the solution should work like that, but it only prints the first element and then memory positions. I am calling my function with: int v={10,12,20,34,45}; getelements(&v,5); Any help? I need to use arithmetic of pointers. Thanks

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  • byte and short data types in Java can accept the value outside the range by explicit cast. The higher data types however can not. Why?

    - by Lion
    Let's consider the following expressions in Java. byte a = 32; byte b = (byte) 250; int i = a + b; This is valid in Java even though the expression byte b = (byte) 250; is forced to assign the value 250 to b which is outside the range of the type byte. Therefore, b is assigned -6 and consequently i is assigned the value 26 through the statement int i = a + b;. The same thing is possible with short as follows. short s1=(short) 567889999; Although the specified value is outside the range of short, this statement is legal. The same thing is however wrong with higher data types such int, double, folat etc and hence, the following case is invalid and causes a compile-time error. int z=2147483648; This is illegal, since the range of int in Java is from -2,147,483,648 to 2147483647 which the above statement exceeds and issues a compile-time error. Why is such not wrong with byte and short data types in Java?

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  • how can i Create looper in timer

    - by Yogesh Ude
    private static final long UPDATE_INTERVAL = 1* 60 * 1000; private Timer timer = new Timer(); public int onStartCommand(Intent intent, int flags, int startId) { timer.scheduleAtFixedRate(new TimerTask() { mLocationManager.requestLocationUpdates( LocationManager.GPS_PROVIDER, LOCATION_INTERVAL, LOCATION_DISTANCE, mLocationListeners[0]); }, 0, UPDATE_INTERVAL); return START_STICKY; }

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  • Dictionary not deserializing

    - by Shadow
    I'm having a problem where one Dictionary in my project is either not serializing or not deserializing. After deserializing, the data I serialized is simply not in the object. Here's the relevant snip of the class being serialized: class Person : ISerializable { private Dictionary<Relation,List<int>> Relationships = new Dictionary<Relation,List<int>>(); public Person(SerializationInfo info, StreamingContext context) { this.Relationships = (Dictionary<Relation, List<int>>) info.GetValue("Relationships", typeof(Dictionary<Relation, List<int>>)); } public void GetObjectData(SerializationInfo info, StreamingContext context) { info.AddValue("Relationships", this.Relationships); } } Note, this is binary serialization. Everything else in the project serializes and deserialzes correctly.

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  • Using template specialization in C++

    - by user550413
    How can I write a function using template specialization that has 2 different input types and an output type: template <class input1, class input2, class output> and return the sum of the 2 numbers (integers/doubles). However, if I get 2 integers I want to return an integer type but for any other combinations of integer and double I'll always return double. I am trying to do that without using directly the '+' operator but having the next functions instead: double add_double_double(double a, double b) {return (a+b);} double add_int_double(int a, double b) {return ((double)(a)+b);} int add_int_int(int a, int b) {return (a+b);}

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  • operator << : std::cout << i << (i << 1);

    - by Oops
    Hi, I use the stream operator << and the bit shifting operator << in one line. I am a bit confused, why does code A) not produce the same output than code B)? A) int i = 4; std::cout << i << " " << (i << 1) << std::endl; //4 8 B) myint m = 4; std::cout << m << " " << (m << 1) << std::endl; //8 8 class myint: class myint { int i; public: myint(int ii) { i = ii; } inline myint operator <<(int n){ i = i << n; return *this; } inline operator int(){ return i; } }; thanks in advance Oops

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  • Pthread - setting scheduler parameters

    - by Andna
    I wanted to use read-writer locks from pthread library in a way, that writers have priority over readers. I read in my man pages that If the Thread Execution Scheduling option is supported, and the threads involved in the lock are executing with the scheduling policies SCHED_FIFO or SCHED_RR, the calling thread shall not acquire the lock if a writer holds the lock or if writers of higher or equal priority are blocked on the lock; otherwise, the calling thread shall acquire the lock. so I wrote small function that sets up thread scheduling options. void thread_set_up(int _thread) { struct sched_param *_param=malloc(sizeof (struct sched_param)); int *c=malloc(sizeof(int)); *c=sched_get_priority_min(SCHED_FIFO)+1; _param->__sched_priority=*c; long *a=malloc(sizeof(long)); *a=syscall(SYS_gettid); int *b=malloc(sizeof(int)); *b=SCHED_FIFO; if (pthread_setschedparam(*a,*b,_param) == -1) { //depending on which thread calls this functions, few thing can happen if (_thread == MAIN_THREAD) client_cleanup(); else if (_thread==ACCEPT_THREAD) { pthread_kill(params.main_thread_id,SIGINT); pthread_exit(NULL); } } } sorry for those a,b,c but I tried to malloc everything, still I get SIGSEGV on the call to pthread_setschedparam, I am wondering why?

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  • Strange python error

    - by Werner
    Hi, I am trying to write a python program that calculates a histogram, given a list of numbers like: 1 3 2 3 4 5 3.2 4 2 2 so the input parameters are the filename and the number of intervals. The program code is: #!/usr/bin/env python import os, sys, re, string, array, math import numpy Lista = [] db = sys.argv[1] db_file = open(db,"r") ic=0 nintervals= int(sys.argv[2]) while 1: line = db_file.readline() if not line: break ll=string.split(line) #print ll[6] Lista.insert(ic,float(ll[0])) ic=ic+1 lmin=min(Lista) print "min= ",lmin lmax=max(Lista) print "max= ",lmax width=666.666 width=(lmax-lmin)/nintervals print "width= ",width nelements=len(Lista) print "nelements= ",nelements print " " Histogram = numpy.zeros(shape=(nintervals)) for item in Lista: #print item int_number = 1 + int((item-lmin)/width) print " " print "item,lmin= ",item,lmin print "(item-lmin)/width= ",(item-lmin)," / ",width," ====== ",(float(item)-float(lmin))/float(width) print "int((item-lmin)/width)= ",int((item-lmin)/width) print item , " belongs to interval ", int_number, " which is from ", lmin+width*(int_number-1), " to ",lmin+width*int_number Histogram[int_number] = Histogram[int_number] + 1 4 but somehow I am completely lost, I get strange errors, can anybody help¿ Thanks

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  • Return the difference between the lowest and highest key

    - by stan
    This is a past exam paper i am attempting and have no way to check if the out put is correct as i am not capable of building one of these things the question is in the title class Tree{ Tree left; Tree right; int key; public static int span(Tree tree) { if ( tree == null ){ return null; } if( tree.left != null) int min = span(tree.left); } if( tree.right != null){ int max = span(tree.right); } return max - min; } } Could anyone suggest what i need to change to get 5/5 marks :D - the only thing we have to do is write the span method, the header was given for us Thanks

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  • How is this function being made use of?

    - by Kay
    Hello all, I am just studying a few classes given to me by my lecturer and I can't understand how the function heapRebuild is being made used of! It doesn't change any global variables and it doesn't print out anything ad it doesn't return anything - so should this even work? It shouldn't, should it? If you were told to make use of heapRebuild to make a new function removeMac would you edit heapRebuild? public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; public T removeMax(){ T rootItem = heap[0]; heap[0] = heap[lastIndex-1]; lastIndex--; heapRebuild(heap, 0, lastIndex); return rootItem; } protected void heapRebuild(T[ ] items, int root, int size){ int child = 2*root+1; if( child < size){ int rightChild = child+1; if ((rightChild < size) && (items[rightChild].compareTo(items[child]) > 0)){ child = rightChild; } if (items[root].compareTo(items[child]) < 0){ T temp = items[root]; items[root] = items[child]; items[child] = temp; heapRebuild(items, child, size);} } } }

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  • Is it possible to embed C code in a C# project?

    - by Jonathan
    I know that it's possible to compile my C code into a dll, and then use P/Invoke to call that code. What I wondered if it was possible to have a chunk of C code embedded directly in my code, perhaps only available to one class... Something like this (non-working) example: public class MyClass { extern "C" { int do_something_in_c(int i) { return i*2; } } public int DoSomething(int value) { return do_something_in_c(value); } } I've been trying for a few hours using Visual Studio 2008, but I'm not getting anywhere, and I suspect that it isn't actually possible. Can anyone confirm or deny this? Thanks.

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  • Different sizes of same strings - Telnet programming

    - by tommyogp
    Hi all, I have been trying to create an iphone app sending telnet command. However what puzzling me is that the sizes of certain strings are so much different, particularly when they include \n or \r. I listed out a few examples. Please assist. const char *a = "play 25\n"; int sizeBitA1 = sizeof(a); // 8 units int sizeBitA2 = sizeof("play 25\n"); // 9 units const char *b = "\r\n"; int sizeBitB1 = sizeof(b); // 8 units int sizeBitB2 = sizeof("\r\n"); // 3 units

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  • Pass reference to ArrayLists to a method.

    - by bhavna raghuvanshi
    here is the whole program: public class ListMerge { public static void main( String[] args) { Scanner input = new Scanner(System.in); System.out.println ("Input length of arraylist 1:"); int n = input.nextInt(); ArrayList x = new ArrayList(); ArrayList y = new ArrayList(); for (int i = 0; i < n; i++) { System.out.println ("Input x[ " + i +"] :" ); x.add(new Integer(i)); } System.out.println ("Input length of arraylist 2:"); int m = input.nextInt(); for (int i = 0; i < m; i++) { System.out.println ("Input y[ " + i +"] :" ); y.add(new Integer(i)); } } list int merge(ArrayList x, ArrayList y) { List all = new ArrayList(); all.addAll(x); all.addAll(y); System.out.println(all); return all; } } also tell me how do i call the function merge?

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  • Thread-safe get (accessor method)

    - by sonofdelphi
    I'm currently using the following code for thread-safe access of a variable. int gnVariable; void getVariableValue(int *pnValue) { acquireLock(); //Acquires the protection mechanism *pnValue = gnVariable; releaseLock(); //Releasing the protection mechanism } I would like to change my API signature to a more user-friendly int getVariableValue(void); How should I rewrite the function - such that the users of the API don't have to bother about the locking/unlocking details?

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  • Throwing out of range exception in C++

    - by Shinka
    This code works; int at(int index) { if(index < 1 || index >= size) throw 0; return x[index]; } Yet this doesn't int at(int index) { if(index < 1 || index >= size) throw std::out_of_range; return x[index]; } I get the error "expected primary expression before ';'". Now... it surprises me because I know std::out_of_range exists and I have #include <stdexcept>

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  • passing different structs to a function in c

    - by clear2k
    I have different structures that need to be filled out the same way. The only difference is that they are filled based on different data. I was wondering if it's possible to pass different structures to a certain function. What I have in mind is something like: struct stu1 { char *a; int b; }; struct stu2 { char *a; int b; }; static struct not_sure **some_func(struct not_sure *not_sure_here, original_content_list) { // do something and return passed struct for(i=0; i<size_of_original_content_list; i++){ //fill out passed structure } return the_struct; } int main(int argc, char *argv[]) { return_struct1 = some_func(stu1); return_struct2 = some_func(stu2); // do something separate with each return struct... } Any comments will be appreciate it.

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  • EventHandlers saved to databases.

    - by Stacey
    In a database application (using Sql Server right now, in C#, with Entity Framework 4.0) I have a situation where I need to trigger events when some values change. For instance assume a class "Trackable". class Trackable { string Name { get; set; } int Positive { get; set; } int Negative { get; set; } int Total { get; set; } // event OnChanged } Trackable is represented in the database as follows; table Trackables Id | guid name | varchar(32) positive | int negative | int Total is of course, calculated at runtime. When a trackable event changes, I want to inspect its previous value, and then see what it is changing to, and be capable of reacting accordingly. However different trackables need to trigger different events (to avoid a huge, massive cascading switch/if block). If this were just only C# code it would be easy - but they have to be saved to the database. I can't divide up each different trackable into a different table/class, that would be silly - they are all identical, but the event raised is different based on how they are made. So I guess my question is, is there any way to store an event handler in a database such that.. Trackable t1 = new Trackable() { Name = "Trackable1" OnChange += TrackableChangedEventHandler(OnTrackable1Change) } Trackable t2 = new Trackable() { Name = "Trackable2", OnChange += TrackableChangedEventHandler(OnTrackable2Change) }

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