null pointer - Page 52 - Developer IT

Getting a file pointer from file descriptor

- by Naga Kiran

In PHP 5.2.3, "fdopen" was used to read/write to a file descriptor that's opened by another application. fdopen(<fileDescriptorId>,"rw"); //It worked fine with PHP 5.2.3 After upgrading PHP to 5.3.2, it's throwing "undefined reference to 'fdopen' function". Please suggest whats the replacement for this in PHP 5.3.2 or any workaround.

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using strcpy_s for TCHAR pointer (Microsoft Specific)

- by Yan Cheng CHEOK

I was wondering which is the correct way? _tcscpy(tchar_pointer, _tcslen(tchar_pointer), _T("Hello World")); or _tcscpy(tchar_pointer, _tcsclen(tchar_pointer), _T("Hello World")); or _tcscpy(tchar_pointer, ???, _T("Hello World"));

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Warning: pointer of type 'void *' used in subtraction

- by idealistikz

Although it runs correctly, the following results in the aforementioned compiler warning: return ((item - (my->items))/(my->itemSize)); 'item' is a 'void *'; 'my-items' is a 'void *'; 'my-itemSize' is an 'int' Casting 'item' and 'my-items' as an 'int *' caused the program to run improperly. What is the best way to remove the warning?

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Pointer arithmetic.

- by Knowing me knowing you

Having code: int** a = new int*[2]; a[0] = new int(1); a[1] = new int(2); cout << "a[0] " << a[0] << '\n'; cout << "a[1] " << a[1] << '\n'; cout << "a[2] " << a[2] << '\n'; cout << "a[0] + 1 " << a[0] + 1 << '\n';//WHY THIS ISN'T == a[1] ? cout << "*(a + 1): " << *(a + 1) << '\n'; //WHY THIS IS == a[1] ? cout << "a[0] - a[1] " << static_cast<int>(a[0] - a[1])<< '\n';//WHY THIS IS == 16 not 4? cout << sizeof(int**); Questions are included right next to relevant lines in code.

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Callback function and function pointer trouble in C++ for a BST

- by Brendon C.

I have to create a binary search tree which is templated and can deal with any data types, including abstract data types like objects. Since it is unknown what types of data an object might have and which data is going to be compared, the client side must create a comparison function and also a print function (because also not sure which data has to be printed). I have edited some C code which I was directed to and tried to template, but I cannot figure out how to configure the client display function. I suspect variable 'tree_node' of class BinarySearchTree has to be passed in, but I am not sure how to do this. For this program I'm creating an integer binary search tree and reading data from a file. Any help on the code or the problem would be greatly appreciated :) Main.cpp #include "BinarySearchTreeTemplated.h" #include <iostream> #include <fstream> #include <string> using namespace std; /*Comparison function*/ int cmp_fn(void *data1, void *data2) { if (*((int*)data1) > *((int*)data2)) return 1; else if (*((int*)data1) < *((int*)data2)) return -1; else return 0; } static void displayNode() //<--------NEED HELP HERE { if (node) cout << " " << *((int)node->data) } int main() { ifstream infile("rinput.txt"); BinarySearchTree<int> tree; while (true) { int tmp1; infile >> tmp1; if (infile.eof()) break; tree.insertRoot(tmp1); } return 0; } BinarySearchTree.h (a bit too big to format here) http://pastebin.com/4kSVrPhm

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Pass temporary object to function that takes pointer

- by Happy Mittal

I tried following code : #include<iostream> #include<string> using namespace std; string f1(string s) { return s="f1 called"; } void f2(string *s) { cout<<*s<<endl; } int main() { string str; f2(&f1(str)); } But this code doesn't compile. What I think is : f1 returns by value so it creates temporary, of which I am taking address and passing to f2. Now Please explain me where I am thinking wrong?

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C++: Reference and Pointer question (example regarding OpenGL)

- by Jay

I would like to load textures, and then have them be used by multiple objects. Would this work? class Sprite { GLuint* mTextures; // do I need this to also be a reference? Sprite( GLuint* textures ) // do I need this to also be a reference? { mTextures = textures; } void Draw( textureNumber ) { glBindTexture( GL_TEXTURE_2D, mTextures[ textureNumber ] ); // drawing code } }; // normally these variables would be inputed, but I did this for simplicity. const int NUMBER_OF_TEXTURES = 40; const int WHICH_TEXTURE = 10; void main() { std::vector<GLuint> the_textures; the_textures.resize( NUMBER_OF_TEXTURES ); glGenTextures( NUMBER_OF_TEXTURES, &the_textures[0] ); // texture loading code Sprite the_sprite( &the_textures[0] ); the_sprite.Draw( WHICH_TEXTURE ); } And is there a different way I should do this, even if it would work? Thanks.

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SugarmCRM REST API always returns "null"

- by TuomasR

I'm trying to test out the SugarCRM REST API, running latest version of CE (6.0.1). It seems that whenever I do a query, the API returns "null", nothing else. If I omit the parameters, then the API returns the API description (which the documentation says it should). I'm trying to perform a login, passing as parameter the method (login), input_type and response_type (json) and rest_data (JSON encoded parameters). The following code does the query: $api_target = "http://example.com/sugarcrm/service/v2/rest.php"; $parameters = json_encode(array( "user_auth" => array( "user_name" => "admin", "password" => md5("adminpassword"), ), "application_name" => "Test", "name_value_list" => array(), )); $postData = http_build_query(array( "method" => "login", "input_type" => "json", "response_type" => "json", "rest_data" => $parameters )); echo $parameters . "\n"; echo $postData . "\n"; echo file_get_contents($api_target, false, stream_context_create(array( "http" => array( "method" => "POST", "header" => "Content-Type: application/x-www-form-urlencoded\r\n", "content" => $postData ) ))) . "\n"; I've tried different variations of parameters and using username instead of user_name, and all provide the same result, just a response "null" and that's it.

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How to treat Base* pointer as Derived<T>* pointer?

- by dehmann

I would like to store pointers to a Base class in a vector, but then use them as function arguments where they act as a specific class, see here: #include <iostream> #include <vector> class Base {}; template<class T> class Derived : public Base {}; void Foo(Derived<int>* d) { std::cerr << "Processing int" << std::endl; } void Foo(Derived<double>* d) { std::cerr << "Processing double" << std::endl; } int main() { std::vector<Base*> vec; vec.push_back(new Derived<int>()); vec.push_back(new Derived<double>()); Foo(vec[0]); Foo(vec[1]); delete vec[0]; delete vec[1]; return 0; } This doesn't compile: error: call of overloaded 'Foo(Base*&)' is ambiguous Is it possible to make it work? I need to process the elements of the vector differently, according to their int, double, etc. types.

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Forcing a templated object to construct from a pointer

- by SalamiArmi

I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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C++ arrays as parameters, subscript vs. pointer

- by awshepard

Alright, I'm guessing this is an easy question, so I'll take the knocks, but I'm not finding what I need on google or SO. I'd like to create an array in one place, and populate it inside a different function. I define a function: void someFunction(double results[]) { for (int i = 0; i<100; ++i) { for (int n = 0; n<16; ++n) //note this iteration limit { results[n] += i * n; } } } That's an approximation to what my code is doing, but regardless, shouldn't be running into any overflow or out of bounds issues or anything. I generate an array: double result[16]; for(int i = 0; i<16; i++) { result[i] = -1; } then I want to pass it to someFunction someFunction(result); When I set breakpoints and step through the code, upon entering someFunction, results is set to the same address as result, and the value there is -1.000000 as expected. However, when I start iterating through the loop, results[n] doesn't seem to resolve to *(results+n) or *(results+n*sizeof(double)), it just seems to resolve to *(results). What I end up with is that instead of populating my result array, I just get one value. What am I doing wrong?

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asp.net MVC ActionMethod causing null exception on parameter

- by David Liddle

I am trying to add filter functionality that sends a GET request to the same page to filter records in my table. The problem I am having is that the textbox complains about null object reference when a parameter is not passed. For example, when the person first views the page the url is '/mycontroller/myaction/'. Then when they apply a filter and submit the form it should be something like 'mycontroller/myaction?name=...' Obviously the problem stems from when the name value has not been passed (null) it is still trying to be bound to the 'name' textbox. Any suggestions on what I should do regarding this problem? UPDATE I have tried setting the DefaultValue attribute but I am assuming this is only for route values and not query string values ActionResult MyAction([DefaultValue("")] string name) //Action - /mycontroler/myaction ActionResult MyAction(string name) { ...do stuff } //View <div id="filter"> <% Html.BeginForm("myaction", "mycontroller", FormMethod.Get); %> Name: <%= Html.TextBox("name") %> .... </div> <table>...my list of filtered data

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pointer to a structure in a nested structure

- by dpka6

I have a 6 levels of nested structures. I am having problem with last three levels. The program compiles fine but when I run it crashes with Segmentation fault. There is some problem in assignment is what I feel. Kindly point out the error. typedef struct { char addr[6]; int32_t rs; uint16_t ch; uint8_t ap; } C; typedef struct { C *ap_info; } B; typedef struct { union { B wi; } u; } A; function1(char addr , int32_t rs, uint16_t ch, uint8_t ap){ A la; la.u.wi.ap_info->addr[6] = addr; la.u.wi.ap_info->rs = rs; la.u.wi.ap_info->ch = ch; la.u.wi.ap_info->ap = ap; }

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Different types for declaring pointer variables

- by viswanathan

Consider the below 2 declarations. appears next to the datatype and not next to variable char* ptr1, * ptr2, * ptr3; //all 3 are pointers appears next to the variable and not next to datatype char *ptr1,*ptr2,*ptr3; //again al 3 are pointers Is there any difference in intepretation between the 2 declarations. I know there is no difference in the variables. What is the rationale behind introducing void pointers?

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Make a mouse pointer do a hyper-jump?

- by John M

I run a dual monitor setup. To get from monitor 1 to 2 (or vice-versa) requires lots of unnecessary mouse movement. My thought was to leverage a extra mouse button (I have two) and have the mouse hyper-jump (apologies to Star Trek) from the XY coordinates on monitor 1 to the same XY coordinates on monitor 2. How would I go about doing this? Could it be done via C#?

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How to change the meaning of pointer access operator

- by kumar_m_kiran

Hi All, This may be very obvious question, pardon me if so. I have below code snippet out of my project, #include <stdio.h> class X { public: int i; X() : i(0) {}; }; int main(int argc,char *arv[]) { X *ptr = new X[10]; unsigned index = 5; cout<<ptr[index].i<<endl; return 0; } Question Can I change the meaning of the ptr[index] ? Because I need to return the value of ptr[a[index]] where a is an array for subindexing. I do not want to modify existing source code. Any new function added which can change the behavior is needed. Since the access to index operator is in too many places (536 to be precise) in my code, and has complex formulas inside the index subscript operator, I am not inclined to change the code in many locations. PS : 1. I tried operator overload and came to conclusion that it is not possible. 2. Also p[i] will be transformed into *(p+i). I cannot redefine the basic operator '+'. So just want to reconfirm my understanding and if there are any possible short-cuts to achieve. Else I need fix it by royal method of changing every line of code :) .

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Auto pointer for unsigned char array?

- by Gianluca

I'd need a class like std::auto_ptr for an array of unsigned char*, allocated with new[]. But auto_ptr only calls delete and not delete[], so i can't use it. I also need to have a function which creates and returns the array. I came out with my own implementation within a class ArrayDeleter, which i use like in this example: #include <Utils/ArrayDeleter.hxx> typedef Utils::ArrayDeleter<unsigned char> Bytes; void f() { // Create array with new unsigned char* xBytes = new unsigned char[10]; // pass array to constructor of ArrayDeleter and // wrap it into auto_ptr return std::auto_ptr<Bytes>(new Bytes(xBytes)); } ... // usage of return value { auto_ptr<Bytes> xBytes(f()); }// unsigned char* is destroyed with delete[] in destructor of ArrayDeleter Is there a more elegant way to solve this? (Even using another "popular" library)

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Object-C: initWithContentsOfURL returning null

- by AragornSG

Hey! I'm working on an app that would display a remote html and use local images, so what I'm trying to do is download the HTML of the website and display it as a "local" page, that would have access to images in my bundle. For some reason I can't get initWithContentsOfURL to work. I checked all manuals and examples I could find and it seems that I'm doing it correctly, but the thing just won't work, returns null all the time. The same page loaded with NSURLRequest requestWithURL works fine. Appreciate your help! Here is the code: - (void)awakeFromNib { appURL = @"http://dragontest.fantasy-fan.org"; notConnectedHTML = @"Could not connect."; NSString *seedString = [[NSString alloc] initWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@/seed.php", appURL]]]; NSString *HTMLdata = @""; if (seedString = @"(null)") { NSLog(@"Can't connect on awakeFromNib."); HTMLdata = notConnectedHTML; }else { HTMLdata = [NSString stringWithFormat:@"<body style='padding:0px;margin:0px;'>%@%@</body>", seedString, @"<br><img src='images/Default.png'>"]; } [homeView loadHTMLString:HTMLdata baseURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] resourcePath]]]; }

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C# XNA: What can cause SpriteBatch.End() to throw a NRE?

- by Rosarch

I don't understand what I'm doing wrong here: public void Draw(GameTime gameTime) // in ScreenManager { SpriteBatch.Begin(SpriteBlendMode.AlphaBlend); for (int i = 0; i < Screens.Count; i++) { if (Screens[i].State == Screen.ScreenState.HIDDEN) continue; Screens[i].Draw(gameTime); } SpriteBatch.End(); // null ref exception } SpriteBatch itself is not null. Some more context: public class MasterEngine : Microsoft.Xna.Framework.Game { public MasterEngine() { graphicsDeviceManager = new GraphicsDeviceManager(this); Components.Add(new GamerServicesComponent(this)); // ... spriteBatch = new SpriteBatch(graphicsDeviceManager.GraphicsDevice); screenManager = new ScreenManager(assets, gameEngine, graphicsDeviceManager.GraphicsDevice, spriteBatch); } //... protected override void Draw(GameTime gameTime) { screenManager.Draw(gameTime); // calls the problematic method base.Draw(gameTime); } } Am I failing to initialize something properly? UPDATE: As an experiment, I tried this to the constructor of MasterEngine: spriteBatch = new SpriteBatch(graphicsDeviceManager.GraphicsDevice); spriteBatch.Begin(); spriteBatch.DrawString(assets.GetAsset<SpriteFont>("calibri"), "ftw", new Vector2(), Color.White); spriteBatch.End(); This does not cause a NRE. hmm.... UPDATE 2: This does cause an NRE: protected override void Draw(GameTime gameTime) { spriteBatch.Begin(); spriteBatch.End(); // boned here //screenManager.Draw(gameTime); base.Draw(gameTime); }

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get data from to tables !

- by mehdi

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Initializing a char array through passed pointer segfaults

- by Bitgarden

Ie., why does the following work: char* char_array(size_t size){ return new char[size]; } int main(){ const char* foo = "foo"; size_t len = strlen(foo); char* bar=char_array(len); memset(bar, 0, len+1); } But the following segfaults: void char_array(char* out, size_t size){ out= new char[size]; } int main(){ const char* foo = "foo"; size_t len = strlen(foo); char* bar; char_array(bar, len); memset(bar, 0, len+1); }

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Objective-c pointer assignment and reassignment dilema

- by moshe

Hi, If I do this: 1 NSMutableArray *near = [[NSMutableArray alloc] init]; 2 NSMutableArray *all = [[NSMutableArray alloc] init]; 3 NSMutableArray *current = near; 4 current = all; What happens to near? At line 3, am I setting current to point to the same address as near so that I now have two variables pointing to the same place in memory, or am I setting current to point to the location of near in memory such that I now have this structure: current - near - NSMutableArray The obvious difference would be the value of near at line 4. If the former is happening, near is untouched and still points to its initial place in memory. If the latter is happening,

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what is a pointer in c?

- by mohanvydehi

What is ponter?

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Convert char pointer (char*) to struct

- by InfinateOne

I have a struct: //Custom packet structure. struct UserPacket { __int64 pingTime; } CustomPacket; I have already figured out how to convert it to a char*. Now I want to convert the char* back to the struct. Any suggestions?

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C++ function-pointer and inheritance

- by pingvinus

In parent class I have function, that operates under an array of functions, declared in child-class, number of functions for every child-class may vary. But since every function uses some object-variables, I can't declare them as static. I've try to do something like this: class A { public: typedef int (A::*func)(); func * fs; void f() { /*call functions from this->fs*/ } }; class B : public A { public: int smth; B(int smth) { this->smth = smth; this->fs = new func[1]; fs[0] = &B::f; } int f() { return smth + 1; } }; But, obviously it doesn't work. Any suggestions?

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- by Naga Kiran

- by Yan Cheng CHEOK

- by idealistikz

- by Knowing me knowing you

- by Brendon C.

- by Happy Mittal

- by Jay

- by TuomasR

- by dehmann

- by SalamiArmi

- by awshepard

- by David Liddle

- by dpka6

- by viswanathan

- by John M

- by kumar_m_kiran

- by Gianluca

- by AragornSG

- by Rosarch

- by mehdi

- by Bitgarden

- by moshe

- by mohanvydehi

- by InfinateOne

- by pingvinus

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