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  • Why doesn't g++ pay attention to __attribute__((pure)) for virtual functions?

    - by jchl
    According to the GCC documentation, __attribute__((pure)) tells the compiler that a function has no side-effects, and so it can be subject to common subexpression elimination. This attribute appears to work for non-virtual functions, but not for virtual functions. For example, consider the following code: extern void f( int ); class C { public: int a1(); int a2() __attribute__((pure)); virtual int b1(); virtual int b2() __attribute__((pure)); }; void test_a1( C *c ) { if( c->a1() ) { f( c->a1() ); } } void test_a2( C *c ) { if( c->a2() ) { f( c->a2() ); } } void test_b1( C *c ) { if( c->b1() ) { f( c->b1() ); } } void test_b2( C *c ) { if( c->b2() ) { f( c->b2() ); } } When compiled with optimization enabled (either -O2 or -Os), test_a2() only calls C::a2() once, but test_b2() calls b2() twice. Is there a reason for this? Is it because, even though the implementation in class C is pure, g++ can't assume that the implementation in every subclass will also be pure? If so, is there a way to tell g++ that this virtual function and every subclass's implementation will be pure?

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  • Please explain class methods

    - by user1209902
    I'm finding it difficult to understand when it is necessary to create class methods. From what I've read, they are important for creating new objects, but I do not see how. The following class create a simple shape black rectangle. Can anyone show me how to incorporate a class method to do something that I could not do with an instance method? Shape.h #import <UIKit/UIKit.h> @interface Shape : UIView; - (id) initWithX: (int)xVal andY: (int)yVal; @end Shape.m #import "Shape.h" @implementation Shape - (id) initWithX:(int )xVal andY:(int)yVal { self = [super init]; UIView *shape = [[UIView alloc] initWithFrame:CGRectMake(xVal, yVal, 10, 10)]; shape.backgroundColor = [UIColor blackColor]; [self addSubview:shape]; return self; } @end

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  • C++ enum casting and templates

    - by JP
    I get the following error with VS2008: Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast) When casting a down casting a ClassA to ClassA_1 and ClassA_1 is a templated class that received an enum for parameter such as: ClassA { virtual ~ClassA(){}; } template <class Param1> ClassA_1 : public ClassA { public: //constructor ClassA_1(Param1 p1) { _p1 = p1; } Param1 _p1; } So I have a upcasted ClassA a = new ClassA_1<myenum>(); When I need to do this: ClassA_1<myenum> a1 = (ClassA_1<myenum> a); // This fails ... The only way it works is: ClassA_1<int> a1 = (ClassA_1<int> a); but this break my template as it must always deal with int... How to properly cast a enum that is now a int, back into the enum?

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  • Are there drawbacks to altering MySQL table data types?

    - by Tower
    Hi, I'm wondering that how much worried I should be about data types. I can easily jump from TINYINT to SMALLINT and from SMALLINT to INT, but are there any drawbacks to this? Obviously situations like from text to int will have consequences, but I'm talking about situations like INT-BIGINT, TINYTEXT-TEXT, etc.

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  • Memory error, access violation.

    - by Ordo
    Hello! I'm learning C on my own and as a exercise i have written a program but it does not work. The program is splitted into 3 parts. A header file, a main file for executing the program a file to define the functions. I'm not using all the functions yet but that shouldn't be the problem. Here is my header file, nothing special in it. #ifndef EMPLOYEE_H #define EMPLOYEE_H struct Employee { char first[21]; char last[21]; char title[21]; int salary; }; struct Employee* createEmployee(char*, char*, char*, int); // Creates a struct Employee object on the heap. char* getfirstname (struct Employee*); char* getlastname (struct Employee*); char* gettitle (struct Employee*); int getsalary (struct Employee*); void setfirstname (struct Employee*, char*); void setlastname (struct Employee*, char*); void settitle (struct Employee*, char*); void setsalary (struct Employee*, int); void printEmployee(struct Employee*); #endif In this file i define the functions and how they work: #include "7.1.h" #include <stdio.h> #include <stdlib.h> #include <string.h> struct Employee* createEmployee(char* first, char* last, char* title, int salary) // Creates a struct Employee object on the heap. { struct Employee* p = (struct Employee*) malloc(sizeof(struct Employee)); if (p != NULL) { strcpy(p->first, first); strcpy(p->last, last); strcpy(p->title, title); p->salary, salary; } return p; } char* getfirstname (struct Employee* p) { if (p != NULL) return p ? p->first : ""; } char* getlastname (struct Employee* p) { if (p != NULL) return p ? p->last : ""; } char* gettitle (struct Employee* p) { if (p != NULL) return p ? p->title : ""; } int getsalary (struct Employee* p) { if (p != NULL) return p ? p->salary : 0; } void setfirstname (struct Employee* p, char* first) { if (p != NULL) strcpy(p->first, first); } void setlastname (struct Employee* p, char* last) { if (p != NULL) strcpy(p->last, last); } void settitle (struct Employee* p, char* title) { if (p != NULL) strcpy(p->title, title); } void setsalary (struct Employee* p, char* salary) { if (p != NULL) p->salary, salary; } void printEmployee(struct Employee* p) { if (p != NULL) { printf("%s, %s, %s, %d", p->first, p->last, p->salary, p->salary ); } } And the last file is used to executed the program/functions: #include "7.1.h" #include <stdio.h> #include <stdlib.h> int main () { char decision; struct Employee emp; struct Employee* emps[3]; for ( int i = 0; i < 1; i ++) { printf("Please type in the emplooyes data.\nFirstname:"); scanf("%s", emp.first); printf("Lastname:"); scanf("%s", emp.last); printf("Title:"); scanf("%s", emp.title); printf("Salary:"); scanf("%d", &emp.salary); emps[i] = createEmployee(emp.first, emp.last, emp.title, emp.salary); } printf("Do you want to print out your information? (Y/N):"); scanf("%c", &decision); if (decision == 'y' || decision == 'Y') { printEmployee(emps[1]); } } I don't know what the problem is. I 'm always getting the following error message after typing in first, last, title and salary for the first time. The error is written in german. It means: Unhandled exception at 0x102de42e (msvcr100d.dll) in 7.1.exe: 0xC0000005: Access violation when writing to 0xCCCCCCCC position. I could fix the first problem with the hints given below. Now when i want to print out the employee data using the function:printEmployee(emps[1]);, I get the same kind of error with access violation.

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  • BlackBerry 5.0 causing full menu to show on navigationClick

    - by jwadsack
    I have a BlackBerry app that is built for 4.5.x SDK. The first page of the app shows a list of fields and each field can be highlighted and clicked. The click action shows a new view with additional information about the field. This all works fine in 4.5, 4.6 and 4.7 and on the sim with 5.0. On a real 9000 running 5.0, when clicking the trackball on an item in the list, the full menu is showing rather than the click event getting consumed (or even fired) for the field. The view is derived from MainScreen and looks something like this: public class ListView extends MainScreen { public ItemCollection list = new ItemCollection; protected void sublayout( int maxWidth, int maxHeight ) { int i = 1; while(( item == (Item)list.nextElement()) != null) { ItemField field = new ItemField(item, i++); add(field); } } } This class does not consume navigationClick, but shouldn't need to, right? The field class does consume navigationClick event: public class ItemField extends Field { protected boolean navigationClick(int status, int time) { controller.showDeal(item.id, Session.current); return true; } } Is there something that changed in 5.0 that I need to add to have this app work the same for all platforms?

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  • How to retrieve all keys (or values) from a std::map?

    - by Owen
    This is one of the possible ways I come out: struct RetrieveKey { template <typename T> typename T::first_type operator()(T keyValuePair) const { return keyValuePair.first; } }; map<int, int> m; vector<int> keys; // Retrieve all keys transform(m.begin(), m.end(), back_inserter(keys), RetrieveKey()); // Dump all keys copy(keys.begin(), keys.end(), ostream_iterator<int>(cout, "\n")); Of course, we can also retrieve all values from the map by defining another functor RetrieveValues. Is there any other way to achieve this easily? (I'm always wondering why std::map does not include a member function for us to do so.)

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  • Looking at the C++ new[] cookie. How portable is this code?

    - by carleeto
    I came up with this as a quick solution to a debugging problem - I have the pointer variable and its type, I know it points to an array of objects allocated on the heap, but I don't know how many. So I wrote this function to look at the cookie that stores the number of bytes when memory is allocated on the heap. template< typename T > int num_allocated_items( T *p ) { return *((int*)p-4)/sizeof(T); } //test #include <iostream> int main( int argc, char *argv[] ) { using std::cout; using std::endl; typedef long double testtype; testtype *p = new testtype[ 45 ]; //prints 45 std::cout<<"num allocated = "<<num_allocated_items<testtype>(p)<<std::endl; delete[] p; return 0; } I'd like to know just how portable this code is.

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  • Code Review: CLR RegexSubstring

    - by OMG Ponies
    Could this be better? .NET 2.0 compatibility for SQL Server 2005: public static SqlString RegexSubstring(SqlString regexpattern, SqlString sourcetext, SqlInt32 start_position) { SqlString result = null; if (!regexpattern.IsNull && !sourcetext.IsNull && !start_position.IsNull) { int start_location = (int)start_position >= 0 ? (int)start_position : 0; Regex RegexInstance = new Regex(regexpattern.ToString()); result = new SqlString(RegexInstance.Match(sourcetext.ToString(), (int)start_position).Value); } return result; }

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  • Optimizing C++ Tree Generation

    - by cam
    Hi, I'm generating a Tic-Tac-Toe game tree (9 seconds after the first move), and I'm told it should take only a few milliseconds. So I'm trying to optimize it, I ran it through CodeAnalyst and these are the top 5 calls being made (I used bitsets to represent the Tic-Tac-Toe board): std::_Iterator_base::_Orphan_me std::bitset<9::test std::_Iterator_base::_Adopt std::bitset<9::reference::operator bool std::_Iterator_base::~_Iterator_base void BuildTreeToDepth(Node &nNode, const int& nextPlayer, int depth) { if (depth > 0) { //Calculate gameboard states int evalBoard = nNode.m_board.CalculateBoardState(); bool isFinished = nNode.m_board.isFinished(); if (isFinished || (nNode.m_board.isWinner() > 0)) { nNode.m_winCount = evalBoard; } else { Ticboard tBoard = nNode.m_board; do { int validMove = tBoard.FirstValidMove(); if (validMove != -1) { Node f; Ticboard tempBoard = nNode.m_board; tempBoard.Move(validMove, nextPlayer); tBoard.Move(validMove, nextPlayer); f.m_board = tempBoard; f.m_winCount = 0; f.m_Move = validMove; int currPlay = (nextPlayer == 1 ? 2 : 1); BuildTreeToDepth(f,currPlay, depth - 1); nNode.m_winCount += f.m_board.CalculateBoardState(); nNode.m_branches.push_back(f); } else { break; } }while(true); } } } Where should I be looking to optimize it? How should I optimize these 5 calls (I don't recognize them=.

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  • Performance side effect with static internal Util classes?

    - by Fostah
    For a util class that contains a bunch of static functionality that's related to the same component, but has different purposes, I like to use static internal classes to organize the functionality, like so: class ComponentUtil { static class Layout { static int calculateX(/* ... */) { // ... } static int calculateY(/* ... */) { // ... } } static class Process { static int doThis(/* ... */) { // ... } static int doThat(/* ... */) { // ... } } } Is there any performance degradation using these internal classes vs. just having all the functionality in the Util class?

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  • Show Dialog Question

    - by Michael Quiles
    How can I get the Xwinnerform to stay on top an keep the main form from being clicked, I tried ShowDialog but I cant get it to work. static public bool CheckWinner(Button[] myControls) { //bolean statement to check for the winner bool gameOver = false; for (int i = 0; i < 8; i++) { int a = Winners[i, 0]; int b = Winners[i, 1]; int c = Winners[i, 2]; Button b1 = myControls[a], b2 = myControls[b], b3 = myControls[c]; if (b1.Text == "" || b2.Text == "" || b3.Text == "") continue; if (b1.Text == b2.Text && b2.Text == b3.Text) { xWinnerForm xWinnerForm = new xWinnerForm(); xWinnerForm.ShowDialog(b1.Text + " is the Winner"); } } return gameOver; } enter code here

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  • MYSQL autoincrement a column or just have an integer, difference?

    - by David19801
    Hi, If I have a column, set as primary index, and set as INT. If I don't set it as auto increment and just insert random integers which are unique into it, does that slow down future queries compared to autincrementing? Does it speed things up if I run OPTIMIZE on a table with its primary and only index as INT? (assuming only 2 columns, and second column is just some INT value) (the main worry is the upper limit on the autoincrement as theres lots of adds and deletes in my table)

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  • Foreach loop problem for Iqueyable object

    - by Vikas
    Hi, Can we use foreach loop for Iqueryable object? I'd like to do something as follow: query = Iqueryable<Myclass> = objDataContext.Myclass; // objDataContext is an object of LINQ datacontext class int[] arr1 = new int[] { 3, 4, 5 }; foreach (int i in arr1) { query = query.Where(q => (q.f_id1 == i || q.f_id2 == i || q.f_id3 == i)); } It gives me wrong output as each time value if i is changed.

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  • Parameter pack argument consumption

    - by yuri kilochek
    It is possible to get the first element of the parameter pack like this template <typename... Elements> struct type_list { }; template <typename TypeList> struct type_list_first_element { }; template <typename FirstElement, typename... OtherElements> struct type_list_first_element<type_list<FirstElement, OtherElements...>> { typedef FirstElement type; }; int main() { typedef type_list<int, float, char> list; typedef type_list_first_element<list>::type element; return 0; } but not possible to similary get the last element like this template <typename... Elements> struct type_list { }; template <typename TypeList> struct type_list_last_element { }; template <typename LastElement, typename... OtherElements> struct type_list_last_element<type_list<OtherElements..., LastElement>> { typedef LastElement type; }; int main() { typedef type_list<int, float, char> list; typedef type_list_last_element<list>::type element; return 0; } with gcc 4.7.1 complaining: error: 'type' in 'struct type_list_last_element<type_list<int, float, char>>' does not name a type What paragraps from the standard describe this behaviour? It seems to me that template parameter packs are greedy in a sense that they consume all matching arguments, which in this case means that OtherElements consumes all three arguments (int, float and char) and then there is nothing left for LastElement so the compilation fails. Am i correct in the assumption? EDIT: To clarify: I am not asking how to extract the last element from the parameter pack, i know how to do that. What i actually want is to pick the pack apart from the back as opposed to the front, and as such recursing all the way to the back for each element would be ineffective. Apparentely reversing the sequence beforehand is the most sensible choice.

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  • Resolve circular typedef dependency?

    - by Nick
    What is the best way to resolve the following circular dependency in typedef-ing these structs? Note the C language tag - I'm looking for a solution in standard gcc C. typedef struct { char* name; int age; int lefthanded; People* friends; } Person; typedef struct { int count; int max; Person* data; } People;

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  • Please see following code and answer

    - by user323422
    template <class T> class _cExplicitInstation { public: void show1(T c) { double d =10.02 ; std::cout<<c; } void show2(T d) { std::cout<<d; } }; template _cExplicitInstation<char>; template void _cExplicitInstation<int>::show1(int c); int main() { _cExplicitInstation<char> abc; _cExplicitInstation<int>().show2(10);// it should show error as i have // explicitly declare for show1() function but its working // can u tell why? }

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  • BlackBerry - Cropping image

    - by rupesh
    Hi all i want to crop a part of Image ,for that i am using following code: int x=20; int y=50; int [] rgbdata=new int[(0+width-x+height-y)* (image.getWidth())]; image.getARGB(rgbdata, 0, image.getWidth(), x, y, width, height); cropedImage=new Bitmap(image.getWidth(),image.getWidth()); cropedImage.setARGB(rgbdata, 0,image.getWidth(), 80,80, width, height); x an y are the position from where the cropping will be done in the rectangular form. but it is not working can any one help me out please. any sample code will work for me. its urgent. thanks in advance

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  • C++ assignment - stylish or performance?

    - by joejax
    Having been writing Java code for many years, I was amazed when I see this C++ statement: int a,b; int c = (a=1, b=a+2, b*3); My question is: Is this a choice of coding style, or it has real benefit? (looking for a practicle use case) I think the compiler will see it the same as following: int a=1, b=a+2; int c = b*3; (What's the offical name for this? I assume it's a standard C/C++ syntax.)

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  • Sql join, 2 tables, same fields

    - by Lobuno
    I have 2 tables. To simplify: Table 1, users: userId int, userName nvarchar(50) Table 2 , messages: msgId int, msgFrom int, msgTo int... msg1 and msg2, both contain userId. Now I want to get all messages, but instead of the msgFrom I want the user name. I know what to do here: select tabMessages.*, tabUsers.userName as Sender from tabMessages inner join tabUsers on msgFrom=userId where msgId = @someParameter; Everything works fine and dandy. The same to get the user name instead of msgTo. Now the problem is, how do I do to get BOTH fields in the same call? I want to get the table as msgId, msgFrom, msgTo, Sender, Recipient. I have tried as: select tabMessages.*, tabUsers.userName as Sender, tabUsers.userName as Recipient from tabMessages inner join tabUsers on msgFrom=userId and msgTo=userId where msgId = @someParameter; but that doesn't work. I'm using Ms sql2000 by the way.

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  • Crash the program with cmd line args

    - by Debanjan
    Lets us consider the following program : #include <stdlib.h> int main(int argc, char **argv){ int a,b; if (argc != 3) return -1; a = atoi(argv[1]); b = atoi(argv[2]); a = b ? a/b : 0; return a; } The task is to crash the program by providing arguments in command-line.

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  • STL: how to overload operator= for <vector> ?

    - by MBes
    There's simple example: #include <vector> int main() { vector<int> veci; vector<double> vecd; for(int i = 0;i<10;++i){ veci.push_back(i); vecd.push_back(i); } vecd = veci; // <- THE PROBLEM } The thing I need to know is how to overload operator = so that I could make assignment like this: vector<double> = vector<int>; I've just tried a lot of ways, but always compiler has been returning errors... Is there any option to make this code work without changing it? I can write some additional lines, but can't edit or delete the existing ones. Ty.

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  • Get the parent class of a null object (C# Reflection)

    - by Nick
    How would I get the parent class of an object that has a value of null? For example... 'Class A' contains 'int? i' which is not set to any value when the class is created. Then in some other place in the code I want to pass in 'i' as a parameter to some function. Using 'i' as the only info, I want to be able to figure out that 'Class A' "owns" 'i'. The reason for this is because 'Class A' also contains some other object, and I want to call this other object's value from that same function mentioned in the above paragraph. Could also be: public class A { public class B { public int? i; public int? j; } B classBInstance = new B(); public string s; } { ... A someClassAInstance = new A(); ... doSomething(someClassAInstance.classBInstance.i); ... } public static bool doSomething(object theObject) { string s = /* SOMETHING on theObject to get to "s" from Class A */; int someValue = (int)theObject; }

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  • how to make the two class fields(not referring any other table) as composite key in hibernate?

    - by M Sach
    i want to make pgId and pgName both as composite key where both pgId anf pgName are assgined values. i am not sure how should i go about it? on net i get examples where composite key column refering to column of some other table but not this kind of scenario? @Entity @Table(name = "PersonDetails") public class PersonDetailsData implements Serializable { private static final long serialVersionUID = 1L; @Id @Basic private int pgId; @Basic(optional = true) @Column(nullable = true) private int orgId; @Basic(optional = true) @Column(nullable = true) private String pgName; public PersonWikiDetailsData() { } public int getPpId() { return ppId; } public void setPpId(int ppId) { this.ppId = ppId; } public String getSpaceName() { return spaceName; } public void setSpaceName(String spaceName) { this.spaceName = spaceName; } }

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  • Calling a C function in a pro*C file

    - by Sachin Chourasiya
    I have these line in my pro*C program. The function initAerage is defined in a C language and I am trying to call this function in a .pcc (pro C++) file. I am getting an error Error: initAverage(int i);was declared before with a different language extern "C" { int initAverage(int i); } Please help

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