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  • Performance when accessing class members

    - by Dr. Acula
    I'm writing something performance-critical and wanted to know if it could make a difference if I use: int test( int a, int b, int c ) { // Do millions of calculations with a, b, c } or class myStorage { public: int a, b, c; }; int test( myStorage values ) { // Do millions of calculations with values.a, values.b, values.c } Does this basically result in similar code? Is there an extra overhead of accessing the class members? I'm sure that this is clear to an expert in C++ so I won't try and write an unrealistic benchmark for it right now

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  • .NET 3.5SP1 64-bit memory model vs. 32-bit memory model

    - by James Dunne
    As I understand it, the .NET memory model on a 32-bit machine guarantees 32-bit word writes and reads to be atomic operations but does not provide this guarantee on 64-bit words. I have written a quick tool to demonstrate this effect on a Windows XP 32-bit OS and am getting results consistent with that memory model description. However, I have taken this same tool's executable and run it on a Windows 7 Enterprise 64-bit OS and am getting wildly different results. Both the machines are identical specs just with different OSes installed. I would have expected that the .NET memory model would guarantee writes and reads to BOTH 32-bit and 64-bit words to be atomic on a 64-bit OS. I find results completely contrary to BOTH assumptions. 32-bit reads and writes are not demonstrated to be atomic on this OS. Can someone explain to me why this fails on a 64-bit OS? Tool code: using System; using System.Threading; namespace ConsoleApplication1 { class Program { static void Main(string[] args) { var th = new Thread(new ThreadStart(RunThread)); var th2 = new Thread(new ThreadStart(RunThread)); int lastRecordedInt = 0; long lastRecordedLong = 0L; th.Start(); th2.Start(); while (!done) { int newIntValue = intValue; long newLongValue = longValue; if (lastRecordedInt > newIntValue) Console.WriteLine("BING(int)! {0} > {1}, {2}", lastRecordedInt, newIntValue, (lastRecordedInt - newIntValue)); if (lastRecordedLong > newLongValue) Console.WriteLine("BING(long)! {0} > {1}, {2}", lastRecordedLong, newLongValue, (lastRecordedLong - newLongValue)); lastRecordedInt = newIntValue; lastRecordedLong = newLongValue; } th.Join(); th2.Join(); Console.WriteLine("{0} =? {2}, {1} =? {3}", intValue, longValue, Int32.MaxValue / 2, (long)Int32.MaxValue + (Int32.MaxValue / 2)); } private static long longValue = Int32.MaxValue; private static int intValue; private static bool done = false; static void RunThread() { for (int i = 0; i < Int32.MaxValue / 4; ++i) { ++longValue; ++intValue; } done = true; } } } Results on Windows XP 32-bit: Windows XP 32-bit Intel Core2 Duo P8700 @ 2.53GHz BING(long)! 2161093208 > 2161092246, 962 BING(long)! 2162448397 > 2161273312, 1175085 BING(long)! 2270110050 > 2270109040, 1010 BING(long)! 2270115061 > 2270110059, 5002 BING(long)! 2558052223 > 2557528157, 524066 BING(long)! 2571660540 > 2571659563, 977 BING(long)! 2646433569 > 2646432557, 1012 BING(long)! 2660841714 > 2660840732, 982 BING(long)! 2661795522 > 2660841715, 953807 BING(long)! 2712855281 > 2712854239, 1042 BING(long)! 2737627472 > 2735210929, 2416543 1025780885 =? 1073741823, 3168207035 =? 3221225470 Notice how BING(int) is never written and demonstrates that 32-bit reads/writes are atomic on this 32-bit OS. Results on Windows 7 Enterprise 64-bit: Windows 7 Enterprise 64-bit Intel Core2 Duo P8700 @ 2.53GHz BING(long)! 2208482159 > 2208121217, 360942 BING(int)! 280292777 > 279704627, 588150 BING(int)! 308158865 > 308131694, 27171 BING(long)! 2549116628 > 2548884894, 231734 BING(int)! 534815527 > 534708027, 107500 BING(int)! 545113548 > 544270063, 843485 BING(long)! 2710030799 > 2709941968, 88831 BING(int)! 668662394 > 667539649, 1122745 1006355562 =? 1073741823, 3154727581 =? 3221225470 Notice that BING(long) AND BING(int) are both displayed! Why are the 32-bit operations failing, let alone the 64-bit ones?

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  • question about in -place sort

    - by davit-datuashvili
    for example we have following array char data[]=new char[]{'A','S','O','R','T','I','N','G','E','X','A','M','P','L','E'}; and index array int a[]=new int[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14}: void insitu(char data[],int a[],N){ for (int i=0;i<N;i++) { char v=data[i]; int j,int k; for (k=i;a[k]!=i;k=a[j];a[j]=j) { j=k;data[k]=data[a[k]; } data[k]=v; a[k]=k; } i have question what is initialize value of j? when i run this code it asks me to initialize j and what should do? }

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  • Preon library problem

    - by Kamahire
    I am using preon lib to parse binary data it contain short, int data The structure as follows @BoundNumber(size="32", byteOrder=ByteOrder.BigEndian) public int time;// @BoundString(size="2") public String alphaChar;// 2 byte array @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code1;//short @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code2;//short @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code3;//short @BoundString(size="8") public String firstName;// 8 byte array @BoundString(size="8") public String middleName;// 8 byte array @BoundString(size="8") public String lastName;// 8 byte array @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code4;//short I am getting correct values for code1, code2, code3 but for code4 it not giving me correct value. It always gives me 0(Zero); When I checked with position of byte array; it shows me correct value. Is there any kind padding require?

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  • Why does a non-constant offsetof expression work?

    - by Chris J. Kiick
    Why does this work: #include <sys/types.h> #include <stdio.h> #include <stddef.h> typedef struct x { int a; int b[128]; } x_t; int function(int i) { size_t a; a = offsetof(x_t, b[i]); return a; } int main(int argc, char **argv) { printf("%d\n", function(atoi(argv[1]))); } If I remember the definition of offsetof correctly, it's a compile time construct. Using 'i' as the array index results in a non-constant expression. I don't understand how the compiler can evaluate the expression at compile time. Why isn't this flagged as an error?

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  • Resizing gives me to heavy image

    - by phenevo
    Hi, I'm resizing jpeg 1200x900 ,556kb by method: public static Image ResizeImage(Image imgToResize, int height) //height=400 { int destWidth; int destHeight; int sourceWidth = imgToResize.Width; int sourceHeight = imgToResize.Height; float nPercent = 0; float nPercentH = 0; nPercentH = ((float)height / (float)sourceHeight); nPercent = nPercentH; destWidth = (int)(sourceWidth * nPercent); destHeight = height; Bitmap b = new Bitmap(destWidth, destHeight); Graphics g = Graphics.FromImage((Image)b); g.InterpolationMode = InterpolationMode.HighQualityBicubic; g.DrawImage(imgToResize, 0, 0, destWidth, destHeight); g.Dispose(); return b; } gives me 555kb 533x400 jpeg. Why this photo is so heavy. For photo jpeg 2111kb 2156x1571 I get 556kb 533x400 jpeg Why in first case is so terrible !

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  • How to do a random-and-unique generator?

    - by javaLearner.java
    I already wrote a random generator which take arguments a and b, where a is minimun and b is maximum value, like this randomGenerator(int a, int b) What I want to do next is: Using a loop, then generate unique number from a to b. Example: I want to have 8 unique numbers, int a = 1; int b = 10; int value; If I do the loop, there is a high % that same number will appear more than once. Any idea how to do it? My own way is: while(int i <= 8){ randomGenerator(a,b); // if value is not in array, then insert into array } I am stuck at the comment part. Is there any way to check if a variable is exists in an array?

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  • How can I get running totals of integer values from a SortedDictionary?

    - by user578083
    SortedDictionary<int, string> typeDictionary = new SortedDictionary<int, string>(); SortedDictionary<int, int> lengthDictionary = new SortedDictionary<int, int>(); lengthDictionary has values in key value pair as follows: <1,20> <2,8> <3,10> <4,5> i want LINQ query which will return me new list like as follows <1,20> <2,20+8=28> // 20 from key 1 <3,28+10=38> // 28 from key 2 <4,38+5=43> // 38 from key 3 Result should like this: <1,20> <2,28> <3,38> <4,43>

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  • QConnect find no such slot on QCombobox by Qt Creater

    - by user2534154
    I create a window inherit from QWidget I set grid layout to that Window I make a function called handleHeroChange(int index) in public slot inside that window I add a Qcombobox to call that function handleHeroChange(int index). Qtcreator keep telling: QObject::connect: No such slot QWidget::handleHeroChange(int) in ../Testing/Window.cpp:92 Why did i do wrong? THE CODE: Window::Window(QWidget *parent) : QWidget(parent) { QGridLayout *grid = new QGridLayout(this); QComboBox *comboHeroClass = new QComboBox(); comboHeroClass->addItem("Witcher"); comboHeroClass->addItem("Maurander"); comboHeroClass->setCurrentIndex(1); grid->addWidget(comboHeroClass, 2,3,1,1); QComboBox::connect(comboHeroClass, SIGNAL(currentIndexChanged(int)),this, SLOT(handleHeroChange(int))); } void Window::handleHeroChange(int index){ QPixmap myImage; if(index == 0){ }else if(index == 1){ } }

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  • C++ inheritance: scoping and visibility of members

    - by Poiuyt
    Can you explain why this is not allowed, #include <stdio.h> class B { private: int a; public: int a; }; int main() { return 0; } while this is? #include <stdio.h> class A { public: int a; }; class B : public A{ private: int a; }; int main() { return 0; } In both the cases, we have one public and one private variable named a in class B. edited now!

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  • Structure within union and bit field

    - by java
    #include <stdio.h> union u { struct st { int i : 4; int j : 4; int k : 4; int l; } st; int i; } u; int main() { u.i = 100; printf("%d, %d, %d", u.i, u.st.i, u.st.l); } I'm trying to figure out the output of program. The first outputs u.i = 100 but I can't understand the output for u.st.i and u.st.l. Please also explain bit fields.

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  • Deleting a element from a vector of pointers in C++.

    - by Kranar
    I remember hearing that the following code is not C++ compliant and was hoping someone with much more C++ legalese than me would be able to confirm or deny it. std::vector<int*> intList; intList.push_back(new int(2)); intList.push_back(new int(10)); intList.push_back(new int(17)); for(std::vector<int*>::iterator i = intList.begin(); i != intList.end(); ++i) { delete *i; } intList.clear() The rationale was that it is illegal for a vector to contain pointers to invalid memory. Now obviously my example will compile and it will even work on all compilers I know of, but is it standard compliant C++ or am I supposed to do the following, which I was told is in fact the standard compliant approach: while(!intList.empty()) { int* element = intList.back(); intList.pop_back(); delete element; }

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  • C++: Could Polymorphic Copy Constructors work?

    - by 0xC0DEFACE
    Consider: class A { public: A( int val ) : m_ValA( val ) {} A( const A& rhs ) {} int m_ValA; }; class B : public A { public: B( int val4A, int val4B ) : A( val4A ), m_ValB( val4B ) {} B( const B& rhs ) : A( rhs ), m_ValB( rhs.m_ValB ) {} int m_ValB; }; int main() { A* b1 = new B( 1, 2 ); A* b2 = new A( *b1 ); // ERROR...but what if it could work? return 0; } Would C++ be broken if "new A( b1 )" was able to resolve to creating a new B copy and returning an A? Would this even be useful?

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  • Difficulty understanding behavior of free()

    - by Rasmi Ranjan Nayak
    int main() { int *ptr, **ptr1; ptr = (int*)malloc(sizeof(int)); ptr1 = (int**)malloc(sizeof(int)); free(ptr); *ptr = 12345; ptr1 = &ptr; //free(ptr); //**ptr1 = 23456; printf("%d \n", **ptr1); system("pause"); return 0; } How does *ptr store the value 12345, when the memory has already been freed? So, now ptr should be pointing to garbage. Why is this happening?

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  • C++ template specialization

    - by user231536
    I have a class template <typename T> class C { static const int K=1; static ostream& print(ostream& os, const T& t) { return os << t;} }; I would like to specialize C for int. //specialization for int template <> C<int>{ static const int K=2; } I want the default print method that works for int to remain and just change the constant. For some specializations, I want to keep K=1 and change the print method because there is no << operator. How do I do this?

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  • question on revrse array

    - by davit-datuashvili
    we know algorithm how reverse array of n integers for (int i=0;i<n/2;i++){ swap(a[i],a[n-1-i]): } is this method better according the speed of algorithm or not because swap using xor is more fast then in other method here is code public class swap{ public static void main(String[]args){ int a[]=new int[]{2,4,5,7,8,11,13,12,14,24}; System.out.println(" array at the begining:"); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } for (int j=0;j<a.length/2;j++){ a[j]^=a[a.length-1-j]; a[a.length-1-j]^=a[j]; a[j]^=a[a.length-1-j]; } System.out.println("reversed array:"); for (int j=0;j<a.length;j++){ System.out.println(a[j]); } } } //result array at the begining: 2 4 5 7 8 11 13 12 14 24 reversed array: 24 14 12 13 11 8 7 5 4 2

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  • question on reverse array

    - by davit-datuashvili
    we know algorithm how reverse array of n integers for (int i=0;i<n/2;i++){ swap(a[i],a[n-1-i]): } is this method better according the speed of algorithm or not because swap using xor is more fast then in other method here is code public class swap { public static void main(String[]args){ int a[]=new int[]{2,4,5,7,8,11,13,12,14,24}; System.out.println(" array at the begining:"); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } for (int j=0;j<a.length/2;j++){ a[j]^=a[a.length-1-j]; a[a.length-1-j]^=a[j]; a[j]^=a[a.length-1-j]; } System.out.println("reversed array:"); for (int j=0;j<a.length;j++){ System.out.println(a[j]); } } } Result: array at the begining: 2 4 5 7 8 11 13 12 14 24 reversed array: 24 14 12 13 11 8 7 5 4 2

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  • Adding interfaces that won't be actually used

    - by devoured elysium
    I currently have two interfaces(that I'll name here IA and IB): interface IA { int Width; int Height; ... } interface IB { int Width; int Height; ... } that share the same two properties: they both have a Width and a Height property. I was thinking if there is any point in defining an IMatrix interface containing a Width and Height properties: interface IMatrix { int Width; int Height; } The thing is that although they share both the same properties, I won't make use of polymorphism with IMatrix in any of my coding: i.e., there won't by any situation where I'll want to use an IMatrix, I'll just want to use IA and IB. Adding an IMatrix seems more like over-engineering than other thing, but I'd like to ask you guys what your opinion is on the matter. Thanks

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  • Outer select column value in joined subquery?

    - by Michael DePetrillo
    Is it possible to use a column value from an outer select within a joined subquery? SELECT table1.id, table2.cnt FROM table1 LEFT JOIN (SELECT COUNT(*) as `cnt` FROM table2 where table2.lt > table1.lt and table2.rt < table1.rt) as table2 ON 1; This results in "Unknown column 'table1.lt' in 'where clause'". Here is the db dump. CREATE TABLE IF NOT EXISTS `table1` ( `id` int(1) NOT NULL, `lt` int(1) NOT NULL, `rt` int(4) NOT NULL) ENGINE=MyISAM DEFAULT CHARSET=latin1; CREATE TABLE IF NOT EXISTS `table2` ( `id` int(1) NOT NULL, `lt` int(1) NOT NULL, `rt` int(4) NOT NULL) ENGINE=MyISAM DEFAULT CHARSET=latin1; INSERT INTO `table1` (`id`, `lt`, `rt`) VALUES (1, 1, 4); INSERT INTO `table2` (`id`, `lt`, `rt`) VALUES (2, 2, 3);

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  • How to sort an array by (smallest, largest, second smallest, second, largest) etc?

    - by Binka
    Any ideas? I can sort an array. But not in this pattern? It needs to sort by the pattern I mentioned above. public void wackySort2(int[] nums) { int sign = 0; int temp = 0; int temp2 = 0; for (int i = 0; i < nums.length; i++) { for (int j = 0; j < nums.length - 1; j++) { if (nums[j] > nums[j + 1]) { temp = nums[j]; nums[j] = nums[j + 1]; nums[j + 1] = temp; //sign = 1; System.out.println("Something has been done"); } } } }

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  • including a std::map within a struct? Is it ok?

    - by user553514
    class X_class{ public: struct extra {int extra1; int extra2; int extra3; }; enum a { n,m}; struct x_struct{ char b; char c; int d; int e; std::map <int, extra> myExtraMap; }; }; in my code I define : x_struct myStruct; why do I get compile errors compiling the above class? The error either says: 1) expected ; before < on the line --- where I defined the map (above) if I eliminate std:: or 2) error: invalid use of ::; error: expected ; before < token

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  • How do i change everything behind a certain point in a Jagged array?

    - by Jack Null
    Say I have a jagged array, and position 2,3 is taken by int 3. Every other spot is filled with int 0. How would I fill all the positions behind 2,3 with a 4? 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 to this: 4 4 4 4 4 4 4 4 4 4 4 4 4 3 0 0 0 0 0 0 0 Ive tried variations of this: int a = 2; int b = 3; for (int x = 0; x < a; x++) { for (int y = 0; y < board.space[b].Length; y++) { board.space[x][y] = 4; } }

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  • Android TextWatcher for more than one EditText

    - by Creative MITian
    I want to implement the TextWatcher interface for more than one EditText fields. Currently I am using : text1.addTextChangedListener(this); text2.addTextChangedListener(this); then overriding the methods in my Activity: public void afterTextChanged(Editable s) {} public void beforeTextChanged(CharSequence s, int start, int count, int after) {} public void onTextChanged(CharSequence s, int start, int before, int count) { // do some operation on text of text1 field // do some operation on text of text2 field } However this is working fine but I'm looking for other ways so that I can explicitly identify that in which EditText field the SoftKeyboard is currently focused.

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  • Change macro in VisualStudio

    - by Vaccano
    The macro 'propdp' creates a dependency property like this: public int MyProperty { get { return (int)GetValue(MyPropertyProperty); } set { SetValue(MyPropertyProperty, value); } } // Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc... public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.Register("MyProperty", typeof(int), typeof(ownerclass), new UIPropertyMetadata(0)); I would like to change it a bit. To look like this: public int MyProperty { get { return (int)GetValue(MyPropertyProperty); } set { SetValue(MyPropertyProperty, value); } } public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.Register("MyProperty", typeof(int), typeof(ownerclass), new UIPropertyMetadata(0)); Can this be done? Does anyone know where to change this?

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