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  • How to explain pointers to a Java/VB programmer

    - by Skeith
    I am writing a game and my friend has offered to help me as it is a RPG and will take a long time to do the "scripting" bit of the game. The problem is IMO he's not that good a programmer :( (add flame war here). He has only programmed in Java and VB and keeps saying really stupid things to me like "Why don't you drag and drop an onClick event" to design my UI when I'm using DirectX. I tried explaining pointers to him but his response was, if it's just a variable that holds a memory address, why don't you just use an int? I create an instance of an attack class and give the creature a pointer to it so if several creatures use the same attack there is only one instance of it. He keeps saying why not put if statements in the creature class for every attack class and set true for the ones that are there. He has programmed mainly in VB and a little in Java just to learn OOP. How can I explain advanced C++ concepts like pointers and memory management to him? He just doesn't understand there are no super functions like form.show in C++.

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  • pointers to member functions in an event dispatcher

    - by derivative
    For the past few days I've been trying to come up with a robust event handling system for the game (using a component based entity system, C++, OpenGL) I've been toying with. class EventDispatcher { typedef void (*CallbackFunction)(Event* event); typedef std::unordered_map<TypeInfo, std::list<CallbackFunction>, hash_TypeInfo > TypeCallbacksMap; EventQueue* global_queue_; TypeCallbacksMap callbacks_; ... } global_queue_ is a pointer to a wrapper EventQueue of std::queue<Event*> where Event is a pure virtual class. For every type of event I want to handle, I create a new derived class of Event, e.g. SetPositionEvent. TypeInfo is a wrapper on type_info. When I initialize my data, I bind functions to events in an unordered_map using TypeInfo(typeid(Event)) as the key that corresponds to a std::list of function pointers. When an event is dispatched, I iterate over the list calling the functions on that event. Those functions then static_cast the event pointer to the actual event type, so the event dispatcher needs to know very little. The actual functions that are being bound are functions for my component managers. For instance, SetPositionEvent would be handled by void PositionManager::HandleSetPositionEvent(Event* event) { SetPositionEvent* s_p_event = static_cast<SetPositionEvent*>(event); ... } The problem I'm running into is that to store a pointer to this function, it has to be static (or so everything leads me to believe.) In a perfect world, I want to store pointers member functions of a component manager that is defined in a script or whatever. It looks like I can store the instance of the component manager as well, but the typedef for this function is no longer simple and I can't find an example of how to do it. Is there a way to store a pointer to a member function of a class (along with a class instance, or, I guess a pointer to a class instance)? Is there an easier way to address this problem?

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  • What are the barriers to understanding pointers and what can be done to overcome them?

    - by David McGraw
    Why are pointers such a leading factor of confusion for many new, and even old, college level students in the C/C++ language? Are there any tools or thought processes that helped you understand how pointers work at the variable, function, and beyond level? What are some good practice things that can be done to bring somebody to the level of, "Ah-hah, I got it," without getting them bogged down in the overall concept? Basically, drill like scenarios.

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  • How to mix textures in DirectX?

    - by tobsen
    I am new to DirectX development and I am wondering if I am taking the wrong route to achieve the following: I would like to mix three textures which contain transparent areas and some solid areas (Red, Blue, Green). The three textures should blend like shown in this example: How can I achieve that in DirectX (preferably in directx9)? A link or example code would be nice. Update: My rendering method looks like this and I still think I am doing it wrong, because the sprite only shows the last texture (nothing is rendered transparent or blended): void D3DTester::render() { d3ddevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0,0,0), 1.0f, 0); d3ddevice->BeginScene(); d3ddevice->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE); d3ddevice->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_ONE); d3ddevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE); LPD3DXSPRITE sprite=NULL; HRESULT hres = D3DXCreateSprite(d3ddevice, &sprite); if(hres != S_OK) { throw std::exception(); } sprite->Begin(D3DXSPRITE_ALPHABLEND); std::vector<LPDIRECT3DTEXTURE9>::iterator it; for ( it=textures.begin() ; it < textures.end(); it++ ) { sprite->Draw(*it, NULL, NULL, NULL, 0xFFFFFFFF); } sprite->End(); d3ddevice->EndScene(); d3ddevice->Present(NULL, NULL, NULL, NULL); } The resulting image looks like this: But I need it to look like this instead: Update2: I figured out that I have to SetRenderState after I use sprite->Begin(D3DXSPRITE_ALPHABLEND); thanks to the hint by Josh Petrie. However, by using this: sprite->Begin(D3DXSPRITE_ALPHABLEND); d3ddevice->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE); d3ddevice->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_ONE); d3ddevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE); std::vector<LPDIRECT3DTEXTURE9>::iterator it; for ( it=textures.begin() ; it < textures.end(); it++ ) { sprite->Draw(*it, NULL, NULL, NULL, 0xFFFFFFFF); } sprite->End(); The sprites colors are becoming transparent towards the background scene e.g.: if I use d3ddevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0,100,21), 1.0f, 0); the result looks like: Is there any way to avoid that? I would like the sprites be transparent to each other but to be still solid to the background. Update3: After having sombody explained to me, how to do what @LaurentCouvidou and @JoshPetrie suggested, I have a working solution and therfore accept the answer: d3ddevice->BeginScene(); D3DCOLOR white = D3DCOLOR_RGBA((UINT)255, (UINT)255, (UINT)255, 255); D3DCOLOR black = D3DCOLOR_RGBA((UINT)0, (UINT)0, (UINT)0, 255); sprite->Begin(D3DXSPRITE_ALPHABLEND); sprite->Draw(pTextureRed, NULL, NULL, NULL, black); sprite->Draw(pTextureGreen, NULL, NULL, NULL, black); sprite->Draw(pTextureBlue, NULL, NULL, NULL, black); sprite->End(); sprite->Begin(D3DXSPRITE_ALPHABLEND); d3ddevice->SetRenderState(D3DRS_ALPHATESTENABLE, TRUE); d3ddevice->SetRenderState(D3DRS_BLENDOP, D3DBLENDOP_ADD); d3ddevice->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_ONE); d3ddevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE); sprite->Draw(pTextureRed, NULL, NULL, NULL, white); sprite->Draw(pTextureGreen, NULL, NULL, NULL, white); sprite->Draw(pTextureBlue, NULL, NULL, NULL, white); sprite->End(); d3ddevice->EndScene(); d3ddevice->Present(NULL, NULL, NULL, NULL);

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  • Reportviewer stored procedure [closed]

    - by Liesl
    I want to write a stored procedure for my invoice reportviewer. After invoice is generated in reportviewer it must also add the data to my Invoice table. This is all my tables in my database: CREATE TABLE [dbo].[Waybills]( [WaybillID] [int] IDENTITY(1,1) NOT NULL, [SenderName] [varchar](50) NULL, [SenderAddress] [varchar](50) NULL, [SenderContact] [int] NULL, [ReceiverName] [varchar](50) NULL, [ReceiverAddress] [varchar](50) NULL, [ReceiverContact] [int] NULL, [UnitDescription] [varchar](50) NULL, [UnitWeight] [int] NULL, [DateReceived] [date] NULL, [Payee] [varchar](50) NULL, [CustomerID] [int] NULL, PRIMARY KEY CLUSTERED CREATE TABLE [dbo].[Customer]( [CustomerID] [int] IDENTITY(1,1) NOT NULL, [customerName] [varchar](30) NULL, [CustomerAddress] [varchar](30) NULL, [CustomerContact] [varchar](30) NULL, [VatNo] [int] NULL, CONSTRAINT [PK_Customer] PRIMARY KEY CLUSTERED ) CREATE TABLE [dbo].[Cycle]( [CycleID] [int] IDENTITY(1,1) NOT NULL, [CycleNumber] [int] NULL, [StartDate] [date] NULL, [EndDate] [date] NULL ) ON [PRIMARY] CREATE TABLE [dbo].[Payments]( [PaymentID] [int] IDENTITY(1,1) NOT NULL, [Amount] [money] NULL, [PaymentDate] [date] NULL, [CustomerID] [int] NULL, PRIMARY KEY CLUSTERED Create table Invoices ( InvoiceID int IDENTITY(1,1), InvoiceNumber int, InvoiceDate date, BalanceBroughtForward money, OutstandingAmount money, CustomerID int, WaybillID int, PaymentID int, CycleID int PRIMARY KEY (InvoiceID), FOREIGN KEY (CustomerID) REFERENCES Customer(CustomerID), FOREIGN KEY (WaybillID) REFERENCES Waybills(WaybillID), FOREIGN KEY (PaymentID) REFERENCES Payments(PaymentID), FOREIGN KEY (CycleID) REFERENCES Cycle(CycleID) ) I want my sp to find all waybills for specific customer in a specific cycle with payments made from this client. All this data must then be added into the INVOICE table. Can someone please help me or show me on the right direction? create proc GenerateInvoice @StartDate date, @EndDate date, @Payee varchar(30) AS SELECT Waybills.WaybillNumber Waybills.SenderName, Waybills.SenderAddress, Waybills.SenderContact, Waybills.ReceiverName, Waybills.ReceiverAddress, Waybills.ReceiverContact, Waybills.UnitDescription, Waybills.UnitWeight, Waybills.DateReceived, Waybills.Payee, Payments.Amount, Payments.PaymentDate, Cycle.CycleNumber, Cycle.StartDate, Cycle.EndDate FROM Waybills CROSS JOIN Payments CROSS JOIN Cycle WHERE Waybills.ReceiverName = @Payee AND (Waybills.DateReceived BETWEEN (@StartDate) AND (@EndDate)) Insert Into Invoices (InvoiceNumber, InvoiceDate, BalanceBroughtForward, OutstandingAmount) Values (@InvoiceNumber, @InvoiceDate, @BalanceBroughtForward, @ OutstandingAmount) go

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  • Fast sketching tools for drawing C/C++ structs, pointers, etc...

    - by tomasorti
    Hi. I would like to know what do you use to sketch relations between different entities in C/C++. This can be a very broad issue, so I'll try to clarify a bit more my question and give an example. I'm looking for something that is simple enough as a user, and let me sketch easily containers, pointers, etc... in an informal way. The aim is to document some structs relations to pass them to junior developers. A look at the drawings is supposed to accelerate the understanding of the code. My solutions at this moment are to use: 1) Paper & pencil. 2) Microsoft PowerPoint/Word Autoshapes. 3) Freeware Dia. Other ones could be: 4) Microsoft Visio, but my company does not own licenses. 5) UML tools. I don't want to go this way. This is what I mean a more formal solution. I know tools like Rational Rose are great, and I tried boUML and violet and they are fine in some parts, but I prefer the flexibility of options 2) or 3). Finally, let me write down a more concrete example: Let's say I what to sketch a map that contains another map as the mapped value, and that one contains a struct as the mapped value, that holds a vector of pointers of a type and a pointer to other type. Also, there exist other structs that hold pointers to the objects pointed by the previous map, so there are objects pointed from different places. This is just one example I have, but you can easily come with one from you experience. What would you use to sketch this example or another similar you have dealt with? Best regards, Tomas.

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  • C++: Vector of objects vs. vector of pointers to new objects?

    - by metamemetics
    Hello, I am seeking to improve my C++ skills by writing a sample software renderer. It takes objects consisting of points in a 3d space and maps them to a 2d viewport and draws circles of varying size for each point in view. Which is better: class World{ vector<ObjectBaseClass> object_list; public: void generate(){ object_list.clear(); object_list.push_back(DerivedClass1()); object_list.push_back(DerivedClass2()); or... class World{ vector<ObjectBaseClass*> object_list; public: void generate(){ object_list.clear(); object_list.push_back(new DerivedClass1()); object_list.push_back(new DerivedClass2()); ?? Would be using pointers in the 2nd example to create new objects defeat the point of using vectors, because vectors automatically call the DerivedClass destructors in the first example but not in the 2nd? Are pointers to new objects necessary when using vectors because they handle memory management themselves as long as you use their access methods? Now let's say I have another method in world: void drawfrom(Viewport& view){ for (unsigned int i=0;i<object_list.size();++i){ object_list.at(i).draw(view); } } When called this will run the draw method for every object in the world list. Let's say I want derived classes to be able to have their own versions of draw(). Would the list need to be of pointers then in order to use the method selector (-) ?

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  • AND is better or using Internal "IF"

    - by BDotA
    In a situation like this:" if ((metadata != null) && (metadata.TypeEnum != VariantInfoMetadata.CellTypeEnum.Status)) do you recommend to keep the code as it is above or do you think it is better to make an internal "if" statement and brake that AND into two sections where "outer if" makes sure metadata is not null and inner if does the rest of the checking. I think this way will take care of possible null refrence exception if value of metadata gets null?

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  • qooxdoo 4.0 : le framework JavaScript adopte les Pointers Events, l'équipe unifie les périphériques

    qooxdoo 4.0 : le framework JavaScript adopte les Pointers Events L'équipe unifie les périphériques (Desktop, Mobile et Site Web)qooxdoo est un framework JavaScript basé sur le système de classes. Il est open source et permet le développement d'applications Web dites « riches » (RIA). La principale nouveauté de la version 4.0 concerne les outils GUI des trois types de plate-formes (site Web, mobile et desktop).Événements indépendants du périphérique d'entréeLes applications qooxdoo peuvent désormais...

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  • Using macro to check null values [migrated]

    - by poliron
    My C code contains many functions with pointers to different structs as parameteres which shouldn't be NULL pointers. To make my code more readable, I decided to replace this code: if(arg1==NULL || arg2==NULL || arg3==NULL...) { return SOME_ERROR; } With that macro: NULL_CHECK(arg1,arg2,...) How should I write it, if the number of args is unknown and they can point to different structs?(I work in C99)

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  • Can a conforming C implementation #define NULL to be something wacky

    - by janks
    I'm asking because of the discussion that's been provoked in this thread: http://stackoverflow.com/questions/2597142/when-was-the-null-macro-not-0/2597232 Trying to have a serious back-and-forth discussion using comments under other people's replies is not easy or fun. So I'd like to hear what our C experts think without being restricted to 500 characters at a time. The C standard has precious few words to say about NULL and null pointer constants. There's only two relevant sections that I can find. First: 3.2.2.3 Pointers An integral constant expression with the value 0, or such an expression cast to type void * , is called a null pointer constant. If a null pointer constant is assigned to or compared for equality to a pointer, the constant is converted to a pointer of that type. Such a pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function. and second: 4.1.5 Common definitions <stddef.h> The macros are NULL which expands to an implementation-defined null pointer constant; The question is, can NULL expand to an implementation-defined null pointer constant that is different from the ones enumerated in 3.2.2.3? In particular, could it be defined as: #define NULL __builtin_magic_null_pointer Or even: #define NULL ((void*)-1) My reading of 3.2.2.3 is that it specifies that an integral constant expression of 0, and an integral constant expression of 0 cast to type void* must be among the forms of null pointer constant that the implementation recognizes, but that it isn't meant to be an exhaustive list. I believe that the implementation is free to recognize other source constructs as null pointer constants, so long as no other rules are broken. So for example, it is provable that #define NULL (-1) is not a legal definition, because in if (NULL) do_stuff(); do_stuff() must not be called, whereas with if (-1) do_stuff(); do_stuff() must be called; since they are equivalent, this cannot be a legal definition of NULL. But the standard says that integer-to-pointer conversions (and vice-versa) are implementation-defined, therefore it could define the conversion of -1 to a pointer as a conversion that produces a null pointer. In which case if ((void*)-1) would evaluate to false, and all would be well. So what do other people think? I'd ask for everybody to especially keep in mind the "as-if" rule described in 2.1.2.3 Program execution. It's huge and somewhat roundabout, so I won't paste it here, but it essentially says that an implementation merely has to produce the same observable side-effects as are required of the abstract machine described by the standard. It says that any optimizations, transformations, or whatever else the compiler wants to do to your program are perfectly legal so long as the observable side-effects of the program aren't changed by them. So if you are looking to prove that a particular definition of NULL cannot be legal, you'll need to come up with a program that can prove it. Either one like mine that blatantly breaks other clauses in the standard, or one that can legally detect whatever magic the compiler has to do to make the strange NULL definition work. Steve Jessop found an example of way for a program to detect that NULL isn't defined to be one of the two forms of null pointer constants in 3.2.2.3, which is to stringize the constant: #define stringize_helper(x) #x #define stringize(x) stringize_helper(x) Using this macro, one could puts(stringize(NULL)); and "detect" that NULL does not expand to one of the forms in 3.2.2.3. Is that enough to render other definitions illegal? I just don't know. Thanks!

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  • Create a JSON Array using Java

    - by Ankur
    Hi I want to create a JSON array. I have tried using: JSONArray jArray = new JSONArray(); while(itr.hasNext()){ int objId = itr.next(); jArray.put(objId, odao.getObjectName(objId)); } results = jArray.toString(); Note: odao.getObjectName(objId) retrieves a name based on the "object Id" which is called objId However I get a very funny looking array like [null,null,null,"SomeValue",null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,"AnotherValue",null,null,null,null,null,null,null,null,null,null,"SomethingElse","AnotherOne","LastOne"] With only "LastOne" being displayed when I retrieve it using jQuery. The Array SHould look like {["3":"SomeValue"],["40":"AnotherValue"],["23":"SomethingElse"],["9":"AnotherOne"],["1":"LastOne"]} The numbers aren't showing up at all for some reason in the array that I am getting

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  • linq hierarchy problem

    - by Pratik
    I reterive a result from sql server as ProjectDetailID,ProjectID,ParentID,...,C1,C2,C3,... where C1 implies(=) companyOne, C2=CompanyTwo ... etc and dynamically can have 'n' companies For time being lets consider only 3 companies, So I get : ProjectDetailID,ProjectID,ParentID,C1,C2,C3 10,1,0,NULL,NULL,NULL 10,2,1,NULL,NULL,NULL 10,3,2,90,NULL,NULL 10,4,2,NULL,60,NULL 10,10,1,70,NULL,NULL 10,5,10,20,40,NULL 10,13,2,NULL,NULL,NULL I want from this following result using LINQ (C#) ProjectDetailID,ProjectID,ParentID,C1,C2,C3 10,1,0,180,100,NULL 10,2,1,90,60,NULL 10,3,2,90,NULL,NULL 10,4,2,NULL,60,NULL 10,10,1,90,40,NULL 10,5,10,20,40,NULL 10,13,2,NULL,NULL,NULL The problem is that at parent level i have null value for a company but at its child i have some value, which i keep on adding and have placed that in parent corresponding to that company only. I am not getting from where to start. Please share your ideas. And i am looking to do this in LINQ using C#

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  • How to have multiple tables with multiple joins

    - by williamsdb
    I have three tables that I need to join together and get a combination of results. I have tried using left/right joins but they don't give the desired results. For example: Table 1 - STAFF id name 1 John 2 Fred Table 2 - STAFFMOBILERIGHTS id staffid mobilerightsid rights --this table is empty-- Table 3 - MOBILERIGHTS id rightname 1 Login 2 View and what I need is this as the result... id name id staffid mobilerightsid rights id rightname 1 John null null null null 1 login 1 John null null null null 2 View 2 Fred null null null null 1 login 2 Fred null null null null 2 View I have tried the following : SELECT * FROM STAFFMOBILERIGHTS SMR RIGHT JOIN STAFF STA ON STA.STAFFID = SMR.STAFFID RIGHT JOIN MOBILERIGHTS MRI ON MRI.ID = SMR.MOBILERIGHTSID But this only returns two rows as follows: id name id staffid mobilerightsid rights id rightname null null null null null null 1 login null null null null null null 2 View Can what I am trying to achieve be done and if so how? Thanks

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  • The best way to have a pointer to several methods - critique requested

    - by user827992
    I'm starting with a short introduction of what i know from the C language: a pointer is a type that stores an adress or a NULL the * operator reads the left value of the variable on its right and use this value as address and reads the value of the variable at that address the & operator generate a pointer to the variable on its right so i was thinking that in C++ the pointers can work this way too, but i was wrong, to generate a pointer to a static method i have to do this: #include <iostream> class Foo{ public: static void dummy(void){ std::cout << "I'm dummy" << std::endl; }; }; int main(){ void (*p)(); p = Foo::dummy; // step 1 p(); p = &(Foo::dummy); // step 2 p(); p = Foo; // step 3 p->dummy(); return(0); } now i have several questions: why step 1 works why step 2 works too, looks like a "pointer to pointer" for p to me, very different from step 1 why step 3 is the only one that doesn't work and is the only one that makes some sort of sense to me, honestly how can i write an array of pointers or a pointer to pointers structure to store methods ( static or non-static from real objects ) what is the best syntax and coding style for generating a pointer to a method?

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  • using "IS" is better or checking for "NOT NULL"

    - by BDotA
    In C#.NET language: This style of coding is recommended or the one below it? if (sheet.Models.Data is GroupDataModel) { GroupDataModel gdm = (GroupDataModel)sheet.Models.Data; Group group = gdm.GetGroup(sheet.ActiveCell.Row.Index); if (group!=null && controller != null) { controller.CheckApplicationState(); } } or this one: var gdm = sheet.Models.Data as GroupDataModel; if (gdm != null) { Group group = gdm.GetGroup(sheet.ActiveCell.Row.Index); if (@group!=null && controller != null) { controller.CheckApplicationState(); } }

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  • Is it a bad idea if equals(null) throws NullPointerException instead?

    - by polygenelubricants
    The contract of equals with regards to null, is as follows: For any non-null reference value x, x.equals(null) should return false. This is rather peculiar, because if o1 != null and o2 == null, then we have: o1.equals(o2) // returns false o2.equals(o1) // throws NullPointerException The fact that o2.equals(o1) throws NullPointerException is a good thing, because it alerts us of programmer error. And yet, that error would not be catched if for various reasons we just switched it around to o1.equals(o2), which would just "silently fail" instead. So the questions are: Why is it a good idea that o1.equals(o2) should return false instead of throwing NullPointerException? Would it be a bad idea if wherever possible we rewrite the contract so that anyObject.equals(null) always throw NullPointerException instead?

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  • How to index a date column with null values?

    - by Heinz Z.
    How should I index a date column when some rows has null values? We have to select rows between a date range and rows with null dates. We use Oracle 9.2 and higher. Options I found Using a bitmap index on the date column Using an index on date column and an index on a state field which value is 1 when the date is null Using an index on date column and an other granted not null column My thoughts to the options are: to 1: the table have to many different values to use an bitmap index to 2: I have to add an field only for this purpose and to change the query when I want to retrieve the null date rows to 3: locks tricky to add an field to an index which is not really needed What is the best practice for this case? Thanks in advance Some infos I have read: Oracle Date Index When does Oracle index null column values?

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  • How to get the first non-null value in Java?

    - by froadie
    Is there a Java equivalent of SQL's COALESCE function? That is, is there any way to return the first non-null value of several variables? e.g. Double a = null; Double b = 4.4; Double c = null; I want to somehow have a statement that will return the first non-null value of a, b, and c - in this case, it would return b, or 4.4. (Something like the sql method - return COALESCE(a,b,c)). I know that I can do it explicitly with something like: return a != null ? a : (b != null ? b : c) But I wondered if there was any built-in, accepted function to accomplish this.

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  • How to declare array of 2D array pointers and access them?

    - by vikramtheone
    Hi Guys, How can I declare an 2D array of 2D Pointers? And later access the individual array elements of the 2D arrays. Is my approach correct? main() { int i, j; int **array[10][10]; int **ptr = NULL; for(i=0;i<10;i++) { for(j=0j<10;j++) { alloc_2D(&ptr, 10, 10); array[i][j] = ptr; } } //After I do this, how can I access the individual 2D array //and then the individual elements of the 2D arrays? } void alloc_2D(float ***memory, unsigned int rows, unsigned int cols) { float **ptr; *memory = NULL; ptr = malloc(rows * sizeof(float*)); if(ptr == NULL) { status = ERROR; printf("\nERROR: Memory allocation failed!"); } else { int i; for(i = 0; i< rows; i++) { ptr[i] = malloc(cols * sizeof(float)); if(ptr[i]==NULL) { status = ERROR; printf("\nERROR: Memory allocation failed!"); } } } *memory = ptr; }

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  • How to approach copying objects with smart pointers as class attributes?

    - by tomislav-maric
    From the boost library documentation I read this: Conceptually, smart pointers are seen as owning the object pointed to, and thus responsible for deletion of the object when it is no longer needed. I have a very simple problem: I want to use RAII for pointer attributes of a class that is Copyable and Assignable. The copy and assignment operations should be deep: every object should have its own copy of the actual data. Also, RTTI needs to be available for the attributes (their type may also be determined at runtime). Should I be searching for an implementation of a Copyable smart pointer (the data are small, so I don't need Copy on Write pointers), or do I delegate the copy operation to the copy constructors of my objects as shown in this answer? Which smart pointer do I choose for simple RAII of a class that is copyable and assignable? (I'm thinking that the unique_ptr with delegated copy/assignment operations to the class copy constructor and assignment operator would make a proper choice, but I am not sure) Here's a pseudocode for the problem using raw pointers, it's just a problem description, not a running C++ code: // Operation interface class ModelOperation { public: virtual void operate = (); }; // Implementation of an operation called Special class SpecialModelOperation : public ModelOperation { private: // Private attributes are present here in a real implementation. public: // Implement operation void operate () {}; }; // All operations conform to ModelOperation interface // These are possible operation names: // class MoreSpecialOperation; // class DifferentOperation; // Concrete model with different operations class MyModel { private: ModelOperation* firstOperation_; ModelOperation* secondOperation_; public: MyModel() : firstOperation_(0), secondOperation_(0) { // Forgetting about run-time type definition from input files here. firstOperation_ = new MoreSpecialOperation(); secondOperation_ = new DifferentOperation(); } void operate() { firstOperation_->operate(); secondOperation_->operate(); } ~MyModel() { delete firstOperation_; firstOperation_ = 0; delete secondOperation_; secondOperation_ = 0; } }; int main() { MyModel modelOne; // Some internal scope { // I want modelTwo to have its own set of copied, not referenced // operations, and at the same time I need RAII to work for it, // as soon as it goes out of scope. MyModel modelTwo (modelOne); } return 0; }

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  • Array of pointers in C++.

    - by Theorem
    I am not understanding the output of this , #include <iostream> using namespace std; // pointers and arrays char ch1 = 'a' , ch2= 'b'; char ch3[6] = {'c', 'd', 'e', 'f', 'g' , 'h'}; char *ptr[3]; int main () { ptr[0] = &ch1 ; ptr[2] = ch3; cout << &ch1 << endl; } The out put is abcdefgh . isn't &ch1 supposed to give the address of ch1 ? I cannot make sense why the output should be abcdefgh.

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