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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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  • Is this pointer initialization necessary?

    - by bstullkid
    Lets say I have the following: CHARLINK * _init_link(CHARLINK **link) { short i; (*link)->cl = (CHARLINK **) calloc(NUM_CHARS, sizeof(CHARLINK *)); for (i = 0; i < NUM_CHARS; i++) (*link)->cl[i] = NULL; return (*link); } Is the loop to initialize each element to NULL necessary or are they automatically NULL from calloc?

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  • how to init and malloc array to pointer on C

    - by DoronS
    Hi all, looks like a memory leak when i try to initializing an array of pointers, this my code: void initLabelTable(){ register int i; hashNode** hp; labelHashTable = (hashNode**) malloc(HASHSIZE*sizeof(hashNode*)); hp = labelHashTable; for(i=0; i<HASHSIZE; i++) { *(hp+i) = NULL; } } any idea?

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  • how to cast c++ smart pointer up and down

    - by user217428
    two clients communicate to each other on top of a message layer in the message body, I need include a field pointing to any data type From client A, I send the field as a shared_ptr to the message layer. I define this field as a shared_ptr in the message layer. But how can I convert this field back to shared_ptr in client B? Or should I define shared_ptr in message layer as something else? Thanks

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  • Question of using static_cast on "this" pointer in a derived object to base class

    - by Johnyy
    Hi, this is an example taken from Effective C++ 3ed, it says that if the static_cast is used this way, the base part of the object is copied, and the call is invoked from that part. I wanted to understand what is happening under the hood, will anyone help? class Window { // base class public: virtual void onResize() { } // base onResize impl }; class SpecialWindow: public Window { // derived class public: virtual void onResize() { // derived onResize impl; static_cast<Window>(*this).onResize(); // cast *this to Window, // then call its onResize; // this doesn't work! // do SpecialWindow- } // specific stuff };

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  • Pointer to local variable

    - by Radek Šimko
    May I have any acces to local variable in different function? If may, how? void replaceNumberAndPrint(int array[3]) { printf("%i\n", array[1]); printf("%i\n", array[1]); } int * getArray() { int myArray[3] = {4, 65, 23}; return myArray; } int main() { replaceNumberAndPrint(getArray()); } The output of the piece of code above: 65 4202656 What am i doing wrong? What the "4202656" means?? Do I have to copy the whole array in the replaceNumberAndPrint() function to be able to access to it more than first times?

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  • 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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  • pass by pointer is not working

    - by user323422
    #include"iostream" class CMessage { public:int a; CMessage(){} ~CMessage(){} }; void Testing(CMessage *f_pMessage)//l_pMessage is output parameter { f_pMessage = new CMessage(); f_pMessage->a = 1; } int main() { CMessage *l_pMessage =NULL; Testing(l_pMessage); std::cout<<l_pMessage->a;//getting l_pMessage = NULL; return 0; } when i called testing then inside testing f_pMessage is getting intialize but as ssoon as i after excuting testing function it should be store in l_Pmessage but it is showing NULL.confussed.....

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  • Release an object without a pointer?

    - by Kai Friis
    I’ve just started developing for iPhone and am trying to get my head around memory management. I made a small program that shows a map and an annotation on the map. For the annotation I made a simple class that implements the MKAnnotation protocol. To create and add the annotation I wrote this: [self.myMapView addAnnotation:[[MyAnnotation alloc] init]]; It worked fine until I tried to release the object. Nothing to release. This is what I would have done in C#, I guess it doesn’t work without garbage collection? So is this the only way to do it? MyAnnotation *myAnnotation = [[MyAnnotation alloc] init]; [self.myMapView addAnnotation: myAnnotation]; [myAnnotation release];

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  • null pointer exception comparing two strings in java.

    - by David
    I got this error message and I'm not quite sure whats wrong: Exception in thread "main" java.lang.NullPointerException at Risk.runTeams(Risk.java:384) at Risk.blobRunner(Risk.java:220) at Risk.genRunner(Risk.java:207) at Risk.main(Risk.java:176) Here is the relevant bits of code (i will draw attention to the line numbers within the error message via comments in the code as well as inputs i put into the program while its running where relevant) public class Risk { ... public static void main (String[]arg) { String CPUcolor = CPUcolor () ; genRunner (CPUcolor) ; //line 176 ... } ... public static void genRunner (String CPUcolor) // when this method runs i select 0 and run blob since its my only option. Theres nothing wrong with this method so long as i know, this is only significant because it takes me to blob runner and because another one of our relelvent line numbers apears. { String[] strats = new String[1] ; strats[0] = "0 - Blob" ; int s = chooseStrat (strats) ; if (s == 0) blobRunner (CPUcolor) ; // this is line 207 } ... public static void blobRunner (String CPUcolor) { System.out.println ("blob Runner") ; int turn = 0 ; boolean gameOver = false ; Dice other = new Dice ("other") ; Dice a1 = new Dice ("a1") ; Dice a2 = new Dice ("a2") ; Dice a3 = new Dice ("a3") ; Dice d1 = new Dice ("d1") ; Dice d2 = new Dice ("d2") ; space (5) ; Territory[] board = makeBoard() ; IdiceRoll (other) ; String[] colors = runTeams(CPUcolor) ; //this is line 220 Card[] deck = Card.createDeck () ; System.out.println (StratUtil.canTurnIn (deck)) ; while (gameOver == false) { idler (deck) ; board = assignTerri (board, colors) ; checkBoard (board, colors) ; } } ... public static String[] runTeams (String CPUcolor) { boolean z = false ; String[] a = new String[6] ; while (z == false) { a = assignTeams () ; printOrder (a) ; boolean CPU = false ; for (int i = 0; i<a.length; i++) { if (a[i].equals(CPUcolor)) CPU = true ; //this is line 384 } if (CPU==false) { System.out.println ("ERROR YOU NEED TO INCLUDE THE COLOR OF THE CPU IN THE TURN ORDER") ; runTeams (CPUcolor) ; } System.out.println ("is this turn order correct? (Y/N)") ; String s = getIns () ; while (!((s.equals ("y")) || (s.equals ("Y")) || (s.equals ("n")) || (s.equals ("N")))) { System.out.println ("try again") ; s = getIns () ; } if (s.equals ("y") || s.equals ("Y") ) z = true ; } return a ; } ... } // This } closes the class The reason i don't think i should be getting a Null:pointerException is because in this line: a[i].equals(CPUcolor) a at index i holds a string and CPUcolor is a string. Both at this point definatly have a value neither is null. Can anyone please tell me whats going wrong?

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  • Defining golang struct function using pointer or not

    - by Jacob
    Can someone explain to me why appending to an array works when you do this: func (s *Sample) Append(name string) { d := &Stuff{ name: name, } s.data = append(s.data, d) } Full code here But not when you do this: func (s Sample) Append(name string) { d := &Stuff{ name: name, } s.data = append(s.data, d) } Is there any reason at all why you would want to use the second example.

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  • Calling member method on unmanaged C++ pointer from C# (I think)

    - by Jacob G
    I apologize in advance if this is a trivial question... I'm pretty C++ / unmanaged dumb. Here's a simplified analog to my setup: --In myUnmanagedObject.h in DLL: class myUnmanagedObject { public: virtual void myMethod(){} } --In MyControl.h in Assembly #1: #pragma make_public(myUnmanagedObject) [event_source(managed)] public ref class MyControl : public System::Windows::Forms::UserControl { public: myUnmanagedObject* GetMyUnmanagedObject(); } --in C# in Assembly #2: unsafe { MyControl temp = new MyControl(); myUnmanagedObject* obj = temp.GetMyUnmanagedObject(); obj-myMethod(); } I get a compile error saying that myUnmanagedObject does not contain a definition for myMethod. Assembly #2 references Assembly #1. Assembly #1 references DLL. If I compile the DLL with /clr and reference it directly from Assembly #2, it makes no difference. How, from C#, do I execute myMethod ?

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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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  • 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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  • C++ Pointer member function with templates assignment with a member function of another class

    - by Agusti
    Hi, I have this class: class IShaderParam{ public: std::string name_value; }; template<class TParam> class TShaderParam:public IShaderParam{ public: void (TShaderParam::*send_to_shader)( const TParam&,const std::string&); TShaderParam():send_to_shader(NULL){} TParam value; void up_to_shader(); }; typedef TShaderParam<float> FloatShaderParam; typedef TShaderParam<D3DXVECTOR3> Vec3ShaderParam; In another class, I have a vector of IShaderParams* and functions that i want to send to "send_to_shader". I'm trying assign the reference of these functions like this: Vec3ShaderParam *_param = new Vec3ShaderParam; _param-send_to_shader = &TShader::setVector3; This is the function: void TShader::setVector3(const D3DXVECTOR3 &vec, const std::string &name){ //... } And this is the class with IshaderParams*: class TShader{ std::vector params; public: Shader effect; std::string technique_name; TShader(std::string& afilename):effect(NULL){}; ~TShader(); void setVector3(const D3DXVECTOR3 &vec, const std::string &name); When I compile the project with Visual Studio C++ Express 2008 I recieve this error: Error 2 error C2440: '=' :can't make the conversion 'void (__thiscall TShader::* )(const D3DXVECTOR3 &,const std::string &)' a 'void (__thiscall TShaderParam::* )(const TParam &,const std::string &)' c:\users\isagoras\documents\mcv\afoc\shader.cpp 127 Can I do the assignment? No? I don't know how :-S Yes, I know that I can achieve the same objective with other techniques, but I want to know how can I do this..

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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