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• Unable to create unmanaged object using new keyword in managed C++

  - by chair79

  Hi all, I've created a class with a boost::unordered_map as a member, Linkage.h #ifndef LINKAGE_H #define LINKAGE_H #include <boost/unordered_map.hpp> class Linkage { private: boost::unordered_map<int, int> m_IOMap; public: .... }; Linkage.cpp #include "stdafx.h" ... // methods and in the managed side of C++, I try to create the pointer of the obj: private: System::Void Form1_Load(System::Object^ sender, System::EventArgs^ e) { Linkage* m_pLink = new Linkage(); ..... } However this produces errors: Error 4 error LNK2005: "private: static unsigned int const boost::detail::type_with_alignment_imp<4>::found" (?found@?$type_with_alignment_imp@$03@detail@boost@@$$Q0IB) already defined in Proj_Test.obj Linkage.obj ..... Error 7 fatal error LNK1169: one or more multiply defined symbols found Could anyone explain to me pls? Thanks.

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• Where in memory are stored nullable types?

  - by Ondrej Slinták

  This is maybe a follow up to question about nullable types. Where exactly are nullable value types (int?...) stored in memory? First I thought it's clear enough, as Nullable<T> is struct and those are value types. Then I found Jon Skeet's article "Memory in .NET", which says: Note that a value type variable can never have a value of null - it wouldn't make any sense, as null is a reference type concept, meaning "the value of this reference type variable isn't a reference to any object at all". I am little bit confused after reading this statement. So let's say I have int? a = null;. As int is normally a value type, is it stored somehow inside struct Nullable<T> in stack (I used "normally" because I don't know what happens with value type when it becomes nullable)? Or anything else happens here - perhaps in heap?

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• Pick Return Values of Stored Procedure

  - by Juergen

  Hi, I have a stored procedure that returns a result with 250!!! columns. But I only need 3 out of the 250. I want to call the SP and put only the 3 column values in a temp table. I don't want to define a temp table with 250 columns! This is how I would like to do it, but this doesn't work of course: create #myTempTable (id int, value1 int, value2 int) insert into #myTempTable exec myBigFatStoredProc Can it be done anyhow? Bye Juergen

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• A table that has relation to itself issue

  - by Mostafa

  Hi , I've defined table with this schema : CREATE TABLE [dbo].[Codings]( [Id] [int] IDENTITY(1,1) NOT NULL, [ParentId] [int] NULL, [CodeId] [int] NOT NULL, [Title] [nvarchar](50) COLLATE Arabic_CI_AI NOT NULL, CONSTRAINT [PK_Codings] PRIMARY KEY CLUSTERED ( [Id] ASC )WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY] ) ON [PRIMARY] And fill it up with data like this : Id ParentId CodeId Title ----------- ----------- ----------- ---------- 1 NULL 0 Gender 2 1 1 Male 3 1 2 Female 4 NULL 0 Educational Level 5 4 1 BS 6 4 2 MS 7 4 3 PHD Now , I'm looking for a solution , in order , When i delete a record that is parent ( like Id= 1 or 4 ), It delete all child automatically ( all records that their ParentId is 1 or 4 ) . I supposed i can do it via relation between Id and Parent Id ( and set cascade for delete rule ) , But when i do that in MMS , the Delete Rule or Update Rule in Properties is disabled . My question is , What can i do to accomplish this ? Thank you

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• Scaling up an image

  - by codefail

  How do I fulfill the condition "returns the entire scaled up image" If I am coding this correctly, scaleColor handles individual colors, getRed handles the red, etc. I am multiplying this by the input, numTimes, which will create a new image that is scaled up it. This scaled up (increase size) is to be returned. This is what I have. Image Image::scaleUp(int numTimes) const { for (int x = 0; x < width; x++) { for (int y = 0; y < height; y++) { pixelData[x][y].scaleColor(pixelData[x][y].scaleRed(pixelData[x][y].getRed()*numTimes)); pixelData[x][y].scaleColor(pixelData[x][y].scaleGreen(pixelData[x][y].getGreen()*numTimes)); pixelData[x][y].scaleColor(pixelData[x][y].scaleBlue(pixelData[x][y].getBlue()*numTimes)); } } //return Image(); }

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• How can I catch runtime error in C++

  - by Yan Cheng CHEOK

  By referring to http://stackoverflow.com/questions/315948/c-catching-all-exceptions try { int i = 0; int j = 0/i; /* Division by 0 */ int *k = 0; std::cout << *k << std::endl; /* De-reference invalid memory location. */ } catch (...) { std::cout << "Opps!" << std::endl; } The above run-time error are unable to be detected. Or, am I having wrong expectation on C++ exception handling feature?

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• Compilation Error on Recursive Variadic Template Function

  - by Maxpm

  I've prepared a simple variadic template test in Code::Blocks, but I'm getting an error: No matching function for call to 'OutputSizes()' Here's my source code: #include <iostream> #include <typeinfo> using namespace std; template <typename FirstDatatype, typename... DatatypeList> void OutputSizes() { std::cout << typeid(FirstDatatype).name() << ": " << sizeof(FirstDatatype) << std::endl; OutputSizes<DatatypeList...>(); } int main() { OutputSizes<char, int, long int>(); return 0; } I'm using GNU GCC with -std=C++0x. Using std=gnu++0x makes no difference.

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• Pointing to vectors

  - by Matt Munson

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

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• Strategy to structure a search index in a relational database

  - by neilc

  I am interested in suggestions for building an efficient and robust structure for indexing products in a new database I am building (i'm using MySql) When a product is entered through the form there are three parts I am interested in indexing for searching purposes. The product title The product description Tags The most important is title, followed by tags, followed by the description. I was thinking of using the following structure CREATE TABLE `searchindex` ( `id` INT NOT NULL , `word` VARCHAR( 255 ) NOT NULL , `weighting` INT NOT NULL , `product_id` INT NOT NULL , PRIMARY KEY ( `id` ) ) Then each time a product is created I would split apart the title, description and tags (removing common words) and award them a weighting. Then it is trivial to select out the words and corresponding products and order them by weighting. Is there a better way to do this? I would be worried that this strategy would slow down over time and as the database filled up.

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• LINQ to SQL -- Can't modify return type of stored procedure.

  - by Kyle Ryan

  When I drag a particular stored procedure into the VS 2008 dbml designer, it shows up with Return Type set to "none", and it's read only so I can't change it. The designer code shows it as returning an int, and if I change that manually, it just gets undone on the next build. But with another (nearly identical) stored procedure, I can change the return type just fine (from "Auto Generated Type" to what I want.) I've run into this problem on two separate machines. Any idea what's going on? Here's the stored procedure that works: USE [studio] GO /****** Object: StoredProcedure [dbo].[GetCourseAnnouncements] Script Date: 05/29/2009 09:44:51 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER OFF GO CREATE PROCEDURE [dbo].[GetCourseAnnouncements] @course int AS SELECT * FROM Announcements WHERE Announcements.course = @course RETURN And this one doesn't: USE [studio] GO /****** Object: StoredProcedure [dbo].[GetCourseAssignments] Script Date: 05/29/2009 09:45:32 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER OFF GO CREATE PROCEDURE [dbo].[GetCourseAssignments] @course int AS SELECT * FROM Assignments WHERE Assignments.course = @course ORDER BY date_due ASC RETURN

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• Dynamically register constructor methods in an AbstractFactory at compile time using C++ templates

  - by Horacio

  When implementing a MessageFactory class to instatiate Message objects I used something like: class MessageFactory { public: static Message *create(int type) { switch(type) { case PING_MSG: return new PingMessage(); case PONG_MSG: return new PongMessage(); .... } } This works ok but every time I add a new message I have to add a new XXX_MSG and modify the switch statement. After some research I found a way to dynamically update the MessageFactory at compile time so I can add as many messages as I want without need to modify the MessageFactory itself. This allows for cleaner and easier to maintain code as I do not need to modify three different places to add/remove message classes: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <inttypes.h> class Message { protected: inline Message() {}; public: inline virtual ~Message() { } inline int getMessageType() const { return m_type; } virtual void say() = 0; protected: uint16_t m_type; }; template<int TYPE, typename IMPL> class MessageTmpl: public Message { enum { _MESSAGE_ID = TYPE }; public: static Message* Create() { return new IMPL(); } static const uint16_t MESSAGE_ID; // for registration protected: MessageTmpl() { m_type = MESSAGE_ID; } //use parameter to instanciate template }; typedef Message* (*t_pfFactory)(); class MessageFactory· { public: static uint16_t Register(uint16_t msgid, t_pfFactory factoryMethod) { printf("Registering constructor for msg id %d\n", msgid); m_List[msgid] = factoryMethod; return msgid; } static Message *Create(uint16_t msgid) { return m_List[msgid](); } static t_pfFactory m_List[65536]; }; template <int TYPE, typename IMPL> const uint16_t MessageTmpl<TYPE, IMPL >::MESSAGE_ID = MessageFactory::Register( MessageTmpl<TYPE, IMPL >::_MESSAGE_ID, &MessageTmpl<TYPE, IMPL >::Create); class PingMessage: public MessageTmpl < 10, PingMessage > {· public: PingMessage() {} virtual void say() { printf("Ping\n"); } }; class PongMessage: public MessageTmpl < 11, PongMessage > {· public: PongMessage() {} virtual void say() { printf("Pong\n"); } }; t_pfFactory MessageFactory::m_List[65536]; int main(int argc, char **argv) { Message *msg1; Message *msg2; msg1 = MessageFactory::Create(10); msg1->say(); msg2 = MessageFactory::Create(11); msg2->say(); delete msg1; delete msg2; return 0; } The template here does the magic by registering into the MessageFactory class, all new Message classes (e.g. PingMessage and PongMessage) that subclass from MessageTmpl. This works great and simplifies code maintenance but I still have some questions about this technique: Is this a known technique/pattern? what is the name? I want to search more info about it. I want to make the array for storing new constructors MessageFactory::m_List[65536] a std::map but doing so causes the program to segfault even before reaching main(). Creating an array of 65536 elements is overkill but I have not found a way to make this a dynamic container. For all message classes that are subclasses of MessageTmpl I have to implement the constructor. If not it won't register in the MessageFactory. For example commenting the constructor of the PongMessage: class PongMessage: public MessageTmpl < 11, PongMessage > { public: //PongMessage() {} /* HERE */ virtual void say() { printf("Pong\n"); } }; would result in the PongMessage class not being registered by the MessageFactory and the program would segfault in the MessageFactory::Create(11) line. The question is why the class won't register? Having to add the empty implementation of the 100+ messages I need feels inefficient and unnecessary.

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• STL Static-Const Member Definitions

  - by javery

  How does the following work? #include <limits> int main() { const int* const foo = &std::numeric_limits<int> ::digits; } I was under the impression that in order to take an address of a static const-ant member we had to physically define it in some translation unit in order to please the linker. That said, after looking at the preprocessed code for this TU, I couldn't find an external definition for the digits member (or any other relevant members). I tested this on two compilers (VC++ 10 and g++ 4.2.4) and got identical results (i.e., it works). Does the linker auto-magically link against an object file where this stuff is defined, or am I missing something obvious here?

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• Get enum by it's inner field

  - by zeroed

  Hi! Have enum with inner fields, kind of map. Now I need to get enum by it's inner field. Wrote this: package test; /** * Test enum to test enum =) */ public enum TestEnum { ONE(1), TWO(2), THREE(3); private int number; TestEnum(int number) { this.number = number; } public TestEnum findByKey(int i) { TestEnum[] testEnums = TestEnum.values(); for (TestEnum testEnum : testEnums) { if (testEnum.number == i) { return testEnum; } } return null; } } But it's not very efficient to look up through all enums each time I need to find appropriate instance. Is there any other way to do the same?

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• Enumerating all combinations of lists of different types

  - by jball

  Given two IEnumberables of different types, what is the best practice (considering readability and maintainability) for iterating over both lists to perform an action on all possible combinations? My initial solution was to use nested foreach loops, iterating over the first IEnumerable, and then within that loop, iterating over the second IEnumerable and passing the value from the outer and the current loop into the target method. Eg.: enum ParamOne { First, Second, Etc } List<int> paramTwo = new List<int>() { 1, 2, 3 }; void LoopExample() { foreach (ParamOne alpha in Enum.GetValues(typeof(ParamOne))) { foreach (int beta in paramTwo) { DoSomething(alpha, beta); } } } I tried to restructure it with LINQ, but ended up with something that had no obvious advantages and seemed less intuitive. A search here shows lots of questions about nesting foreachs to iterate over child properties, but I couldn't find anything about iterating over two distinct lists.

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• Compare rows between 2 tables

  - by arthur

  I am new to SQL and I need to build a database for a grocery store(not real, just a course assignment) i have two fields from two different tables - supplied price - the price that the store buys from the supplier and price that is given to the customers How can I make a constraint that insures that supplied price is lower then the price that is given to the customers? The relevant tables that I have are: CREATE TABLE Supplied_Products( [Supplier ID] Int NOT NULL Foreign Key References Suppliers, [Product ID] Int NOT NULL Foreign Key References Products, Price Float NOT NULL, CHECK (Price0), Constraint PK_Supplied_Products PRIMARY KEY([Supplier ID] ,[Product ID]) ) CREATE TABLE Products( [Product-ID] Int NOT NULL PRIMARY KEY, [Product Name] Varchar(20) NOT NULL, Price Float NOT NULL, [Category-Name] Varchar(20) NOT NULL Foreign Key References Categories, [Weight] Float NOT NULL, [Is Refrigirated] Varchar(1) DEFAULT 'N' CHECK ([Is Refrigirated] in('Y','N')),/* Is Refrigirated can be only Y-yes or N-no*/ CHECK (Price 0) )

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• Spring overloaded constructor injection

  - by noob

  This is the code : public class Triangle { private String color; private int height; public Triangle(String color,int height){ this.color = color; this.height = height; } public Triangle(int height ,String color){ this.color = color; this.height = height; } public void draw() { System.out.println("Triangle is drawn , + "color:"+color+" ,height:"+height); } } The Spring config-file is : <bean id="triangle" class="org.tester.Triangle"> <constructor-arg value="20" /> <constructor-arg value="10" /> </bean> Is there any specific rule to determine which constructor will be called by Spring ?

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• Is Boost.Tuple compatible with C++0x variadic templates ?

  - by Thomas Petit

  Hi, I was playing around with variadic templates (gcc 4.5) and hit this problem : template <typename... Args> boost::tuple<Args...> my_make_tuple(Args... args) { return boost::tuple<Args...>(args...); } int main (void) { boost::tuple<int, char> t = my_make_tuple(8, 'c'); } GCC error message : sorry, unimplemented: cannot expand 'Arg ...' into a fixed-length argument list In function 'int my_make_tuple(Arg ...)' If I replace every occurrence of boost::tuple by std::tuple, it compiles fine. Is there a problem in boost tuple implementation ? Or is this a gcc bug ? I must stick with Boost.Tuple for now. Do you know any workaround ? Thanks.

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• Why won't C++ allow this default value

  - by nieldw

  Why won't GCC allow a default parameter here? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { This is the output I get: graph.h:82: error: default argument given for parameter 2 of ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool)’ graph.h:36: error: after previous specification in ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool)’ Can anyone see why I'm getting this?

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• Why does Color.IsNamedColor not work when I create a color using Color.FromArgb()?

  - by Jon B

  In my app I allow the user to build a color, and then show him the name or value of the color later on. If the user picks red (full red, not red-ish), I want to show him "red". If he picks some strange color, then the hex value would be just fine. Here's sample code that demonstrates the problem: static string GetName(int r, int g, int b) { Color c = Color.FromArgb(r, g, b); // Note that specifying a = 255 doesn't make a difference if (c.IsNamedColor) { return c.Name; } else { // return hex value } } Even with very obvious colors like red IsNamedColor never returns true. Looking at the ARGB values for my color and Color.Red, I see no difference. However, calling Color.Red.GetHashCode() returns a different hash code than Color.FromArgb(255, 0, 0).GetHashCode(). How can I create a color using user specified RGB values and have the Name property come out right?

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• The Columns in table <table> do not match an existing primary key or unique constraint

  - by Sven

  I have 2 tables, Stores - storeId (int) and year (int(4)) both Primary Keys. fruit - fruitId - Primary Key and storeId. I need to create 1 to many relationship between the Store and Fruit (Foreign Key held within Fruit) how ever I always get shown the error - The Columns in table <table> do not match an existing primary key or unique constraint. The type's are both int and named the same. Any help would be appreciate in advance, many thanks.

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• What causes my borderless C++ app to crash when overriding WndProc?

  - by Ste

  I use a form with border NONE. I need to override WndProc for resize and move form. However, using this code, my app crashes! static const int WM_NCHITTEST = 0x0084; static const int HTCLIENT = 1; static const int HTCAPTION = 2; protected: virtual void Form1::WndProc(System::Windows::Forms::Message %m) override { switch (m.Msg) { case WM_NCHITTEST: if (m.Result == IntPtr(HTCLIENT)) { m.Result = IntPtr(HTCAPTION); } break; } Form1::WndProc(m); } virtual System::Windows::Forms::CreateParams^ get() override { System::Windows::Forms::CreateParams^ cp = __super::CreateParams; cp->Style |= 0x40000; return cp; } How can I fix my code not to crash but still allow my form to be moved and resized?

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• Get the lua command when a c function is called

  - by gamernb

  Supposed I register many different function names in Lua to the same function in C. Now, everytime my C function is called, is there a way to determine which function name was invoked? for example: int runCommand(lua_State *lua) { const char *name = // getFunctionName(lua) ? how would I do this part for(int i = 0; i < functions.size; i++) if(functions[i].name == name) functions[i].Call() } int main() { ... lua_register(lua, "delay", runCommand); lua_register(lua, "execute", runCommand); lua_register(lua, "loadPlugin", runCommand); lua_register(lua, "loadModule", runCommand); lua_register(lua, "delay", runCommand); } So, how do I get the name of what ever function called it?

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• Strict pointer aliasing: any solution for a specific problem?

  - by doublep

  I have a problem caused by breaking strict pointer aliasing rule. I have a type T that comes from a template and some integral type Int of the same size (as with sizeof). My code essentially does the following: T x = some_other_t; if (*reinterpret_cast <Int*> (&x) == 0) ... Because T is some arbitary (other than the size restriction) type that could have a constructor, I cannot make a union of T and Int. (This is allowed only in C++0x only and isn't even supported by GCC yet). Is there any way I could rewrite the above pseudocode to preserve functionality and avoid breaking strict aliasing rule? Note that this is a template, I cannot control T or value of some_other_t; the assignment and subsequent comparison do happen inside the templated code. (For the record, the above code started breaking on GCC 4.5 if T contains any bit fields.)

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• dynamic programming: speeding up this function

  - by aristotaly

  i have this program //h is our N static int g=0; int fun(int h){ if(h<=0){ g++; return g; } return g+fun(h-1)+fun(h-4); } is it possible to speed it up using dynamic programming i fugured out this function runs in O(2^n) it means that i suppose to reduce this time but the trouble is that i don get the idea of dinamic programming even a leading hint or a useful link to a resource will do it is a work assingment i do not ask for the solution :) just asking for the right direction

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• Display values inside a JList -

  - by sharon Hwk

  I have a method that returns a HashMap, and is defined as follows; public HashMap<Integer, Animal> allAnimal(){ return returnsAHashMap; } Animal will have the following values in its class: public Animal{ int animalID; String animalName; // i have declared getters/setters } I have a GUI screen which has a JList and it's defined as: l = new JList(); l.setModel(new AbstractListModel() { String[] v = new String[] {"animal id 1", "2", "3"}; public int getSize() { return v.length; } public Object getElementAt(int index) { return v[index]; } }); What I want to do is to display the AnimalID's in the JList. I need to find a way to call the allAnimal() method and display all its Animal Id's in the JList. How can i do this ?

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