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  • STL class for reference-counted pointers?

    - by hasen j
    This should be trivial but I can't seem to find it (unless no such class exists!) What's the STL class (or set of classes) for smart pointers? UPDATE Thanks for the responses, I must say I'm surprised there's no standard implementation. I ended up using this one: http://www.gamedev.net/reference/articles/article1060.asp

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  • Array of function pointers in Java

    - by Waltzy
    I have read this question and I'm still not sure whether it is possible to keep pointers to methods in an array in Java, if anyone knows if this is possible or not it would be a real help. I'm trying to find an elegant solution of keeping a list of Strings and associated functions without writing a mess of hundreds of 'if's. Cheers edit- 'functions' changed to 'methods', seems to bug people.

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  • At What point should you understand pointers?

    - by Vaccano
    I asked a question like this in an interview for a entry level programmer: var instance1 = new myObject{Value = "hello"} var instance2 = instance1; instance1.Value = "bye"; Console.WriteLine(instance1.Value); Console.WriteLine(instance2.Value); The applicant responded with "hello", "bye" as the output. Some of my co-workers said that pointers are not that important anymore or that this question is not a real judge of ability. Are they right?

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  • not so obvious pointers

    - by mike_hornbeck
    I have a class : class X{ public : void f ( int ) ; int a ; } ; And the task is "Inside the code provide declarations for : pointer to int variable of class X pointer to function void(int) defined inside class X pointer to double variable of class X" Ok so pointer to int a will be just int *x = &a, right ? If there is no double in X can I already create pointer to double inside this class ? And the biggest problem is the second task. How one declares pointer to function ?

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  • C++ inheritance and member function pointers

    - by smh
    In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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  • Array of pointers in objective-c

    - by Justin
    I'm getting confused by pointers in objective-c. Basically I have a bunch of static data in my code. static int dataSet0[2][2] = {{0, 1}, {2, 3}}; static int dataSet1[2][2] = {{4, 5}, {6, 7}}; And I want to have an array to index it all. dataSets[0]; //Would give me dataSet0... What should the type of dataSets be, and how would I initialize it?

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  • Trouble using opaque pointers in Objective C++

    - by morgancodes
    The answer to this quesion explains that opaque pointers are a good way to include C++ member variables in an Objective C++ header. I'm getting compile errors when trying to follow the example. Here's the relevant code from my header, with the corresponding compiler errors shown as comments: struct ADSR_opaque; // error: forward declaration of 'struct ADSR_opaque' @interface LoopyPulser : NSObject{ float _pulseRate; UInt32 tickInterval; UInt32 step; InMemoryAudioFile * audioFilePlayer; ADSR_opaque* env; // error: expected specifier-qualifier-list before 'ADSR_opaque' Pattern * pattern; float loopLengthRatio; float volume; } Is there something simple I'm doing wrong here?

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  • Functions as pointers in Objective-C

    - by richman0829
    This is a question from Learn Objective-C on the Mac... Functions as pointers What I typed in, as per the recipe, was: NSString *boolString (BOOL yesNo) { if (yesNo) { return (@"YES"); } else { return (@"NO"); } } // boolString The pointer asterisk in the first line doesn't seem necessary, yet deleting it results in an error message. But what does it do? In NSString * boolString (yesNo); what seems to be going on is a function is defined as a pointer to an NSString. The function without the asterisk NSLog (@"are %d and %d different? %@", 5, 5, boolString(areTheyDifferent)); returns an NSString of YES or NO. But how can it return an NSString when it's a pointer? It might return the ADDRESS of an NSString; or if dereferenced it could return the CONTENTS of that address (an NSString such as YES or NO). Yet I see no place where it is dereferenced.

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  • Dereferencing pointers without pointing them at a variable

    - by Miguel
    I'm having trouble understanding how some pointers work. I always thought that when you created a pointer variable (p), you couldn't deference and assign (*p = value) unless you either malloc'd space for it (p = malloc(x)), or set it to the address of another variable (p = &a) However in this code, the first assignment works consistently, while the last one causes a segfault: typedef struct { int value; } test_struct; int main(void) { //This works int* colin; *colin = 5; //This never works test_struct* carter; carter->value = 5; } Why does the first one work when colin isn't pointing at any spare memory? And why does the 2nd never work? I'm writing this in C, but people with C++ knowledge should be able to answer this as well.

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  • Arrays & Pointers

    - by Thomas
    Hi, Looking for some help with arrays and pointers and explanation of what I am trying to do. I want to create a new array on the heap of type Foo* so that I may later assign objects that have been created else where to this array. I am having troubles understanding what I am creating exactly when I do something like the following. Foo *(*f) = new Foo*[10]; Also once I have created my array how do I access each element for example. (f + 9)->fooMember(); ?????? Thanks in advance.

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  • Function pointers to member functions

    - by Jacob
    There are several duplicates of this but nobody explains why I can use a member variable to store the pointer (in FOO) but when I try it with a local variable (in the commented portion of BAR), it's illegal. Could anybody explain this? #include <iostream> using namespace std; class FOO { public: int (FOO::*fptr)(int a, int b); int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { fptr = &FOO::add_stuff; cout<<(this->*fptr)(a,b)<<endl; } }; class BAR { public: int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { //int (BAR::*fptr)(int a, int b); //fptr = &BAR::add_stuff; //cout<<(*fptr)(a,b)<<endl; } }; int main() { FOO test; test.call_adder(10,20); return 0; }

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  • Understanding c-pointers for rows in 2-dimensional array

    - by utdiscant
    I have the following code: int main() { int n = 3, m = 4, a[n][m], i, j, (* p)[m] = a; for (i = 0; i < n; i++) for (j = 0; j < m; j++) a[i][j] = 1; p++; (*p)[2] = 9; return 0; } I have a hard time understanding what p is here, and the consequences of the operations on p in the end. Can someone give me a brief explanation of what happens. I know c-pointers in their simple settings, but here it get slightly more complicated.

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  • Javascript Pointers question with Dates

    - by Mega Matt
    I noticed this situation in my code (unfortunately), and was able to duplicate it in my own JS file. So I have this code: var date1 = new Date(); // today var date2 = date1; date2 = date2.setDate(date2.getDate() + 1); // what is date1? After this code executes, date1 is today's date + 1! This harkens back to my undergrad days when I learned about pointers, and I guess I'm a little rusty. Is that what's happening here? Obviously I've moved the assignment away from date1, and am only modifying date2, but date1 is being changed. Why is this the case? Incidentally, after this code executes date2 is a long number like 1272123603911. I assume this is the number of seconds in the date, but shouldn't date2 still be a Date object? setDate() should return a Date object... Thanks for the help.

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  • Stucture with array of pointers in C

    - by MVTCplusplus
    What's wrong with this? Can I have an array of pointers to SDL_Surfaces in a struct in C? typedef struct { int next_wheel; int pos_X; int pos_Y; int front_wheel_pos_X; int front_wheel_pos_Y; int velocity; int rear_wheel_pos_X; int rear_wheel_pos_Y; SDL_Surface* body; SDL_Surface* rear_wheel[9]; SDL_Surface* front_wheel[9]; } mars_rover; ... mars_rover* init_rover() { mars_rover* rover = (mars_rover*)malloc(sizeof(mars_rover) + sizeof(SDL_Surface) * 19); ... return rover; } int main() { mars_rover* rover = init_rover(); ... }

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  • pointers for getting elements of an array in C

    - by Manolo
    I am a newbie in C and I would like to get the elements of an array with a function, I have tried different options, but I still do not get the elements. My function is: void getelements(int *a, int cl) { int *p; for (p=&a[0];p<&a[cl];p++) { printf("%d\n",*p); } } I know that the solution should work like that, but it only prints the first element and then memory positions. I am calling my function with: int v={10,12,20,34,45}; getelements(&v,5); Any help? I need to use arithmetic of pointers. Thanks

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  • Structs and pointers

    - by user1763861
    I have a few questions about structs and pointers For this struct: typedef struct tNode_t { char *w; } tNode; How come if I want to change/know the value of *w I need to use t.w = "asdfsd" instead of t->w = "asdfasd"? And I compiled this successfully without having t.w = (char *) malloc(28*sizeof(char)); in my testing code, is there a reason why tt's not needed? Sample main: int main() { tNode t; char w[] = "abcd"; //t.word = (char *) malloc(28*sizeof(char)); t.word = w; printf("%s", t.word); } Thanks.

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  • function objects versus function pointers

    - by kumar_m_kiran
    Hi All, I have two questions related to function objects and function pointers, Question : 1 When I read the different uses sort algorithm of STL, I see that the third parameter can be a function objects, below is an example class State { public: //... int population() const; float aveTempF() const; //... }; struct PopLess : public std::binary_function<State,State,bool> { bool operator ()( const State &a, const State &b ) const { return popLess( a, b ); } }; sort( union, union+50, PopLess() ); Question : Now, How does the statement, sort(union, union+50,PopLess()) work? PopLess() must be resolved into something like PopLess tempObject.operator() which would be same as executing the operator () function on a temporary object. I see this as, passing the return value of overloaded operation i.e bool (as in my example) to sort algorithm. So then, How does sort function resolve the third parameter in this case? Question : 2 Question Do we derive any particular advantage of using function objects versus function pointer? If we use below function pointer will it derive any disavantage? inline bool popLess( const State &a, const State &b ) { return a.population() < b.population(); } std::sort( union, union+50, popLess ); // sort by population PS : Both the above references(including example) are from book "C++ Common Knowledge: Essential Intermediate Programming" by "Stephen C. Dewhurst". I was unable to decode the topic content, thus have posted for help. Thanks in advance for your help.

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  • Dangling pointers and double free

    - by user151410
    After some painful experiences, I understand the problem of dangling pointers and double free. I am seeking proper solutions. aStruct has a number of fields including other arrays. aStruct *A=NULL, *B = NULL; A = (aStruct*) calloc(1, sizeof(sStruct)); B = A; free_aStruct(A); ... //bunch of other code in various places. ... free_aStruct(B); Is there any way to write free_aStruct(X) so that free_aStruct(B) exists gracefully?? void free_aStruct(aStruct *X){ if (X ! = NULL){ if (X->a != NULL){free(X->a); x->a = NULL;} free(X); X = NULL; } } Doing above only sets A = NULL when free_aStruct(A); is called. B is now dangling. How can this situation be avoided / remedied? Is reference counting the only viable solution? or, are there other "defensive" free approaches, to prevent free_aStruct(B); from exploding? Thanks, Russ

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  • Trouble with pointers and references in C++

    - by KingNestor
    I have a PolygonList and a Polygon type, which are std::lists of Points or lists of lists of points. class Point { public: int x, y; Point(int x1, int y1) { x = x1; y = y1; } }; typedef std::list<Point> Polygon; typedef std::list<Polygon> PolygonList; // List of all our polygons PolygonList polygonList; However, I'm confused on reference variables and pointers. For example, I would like to be able to reference the first Polygon in my polygonList, and push a new Point to it. So I attempted to set the front of the polygonList to a Polygon called currentPolygon like so: Polygon currentPolygon = polygonList.front(); currentPolygon.push_front(somePoint); and now, I can add points to currentPolygon, but these changes end up not being reflected in that same polygon in the polygonList. Is currentPolygon simply a copy of the Polygon in the front of polygonList? When I later iterate over polygonList all the points I've added to currentPolygon aren't shown. It works if I do this: polygonList.front().push_front(somePoint); Why aren't these the same and how can I create a reference to the physical front polygon rather than a copy of it?

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  • Obj-C: Passing pointers to initialized classes in other classes

    - by FnGreg7
    Hey all. I initialized a class in my singleton called DataModel. Now, from my UIViewController, when I click a button, I have a method that is trying to access that class so that I may add an object to one of its dictionaries. My get/set method passes back the pointer to the class from my singleton, but when I am back in my UIViewController, the class passed back doesn't respond to methods. It's like it's just not there. I think it has something to do with the difference in passing pointers around classes or something. I even tried using the copy method to throw a copy back, but no luck. UIViewController: ApplicationSingleton *applicationSingleton = [[ApplicationSingleton alloc] init]; DataModel *dataModel = [applicationSingleton getDataModel]; [dataModel retrieveDataCategory:dataCategory]; Singleton: ApplicationSingleton *m_instance; DataModel *m_dataModel; - (id) init { NSLog(@"ApplicationSingleton.m initialized."); self = [super init]; if(self != nil) { if(m_instance != nil) { return m_instance; } NSLog(@"Initializing the application singleton."); m_instance = self; m_dataModel = [[DataModel alloc] init]; } NSLog(@"ApplicationSingleton init method returning."); return m_instance; } -(DataModel *)getDataModel { DataModel *dataModel_COPY = [m_dataModel copy]; return dataModel_COPY; } For the getDataModel method, I also tried this: -(DataModel *)getDataModel { return m_dataModel; } In my DataModel retrieveDataCategory method, I couldn't get anything to work. I even just tried putting a NSLog in there but it never would come onto the console. Any ideas?

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  • C++ trouble with pointers to objects

    - by Zibd
    I have a class with a vector of pointers to objects. I've introduced some elements on this vector, and on my main file I've managed to print them and add others with no problems. Now I'm trying to remove an element from that vector and check to see if it's not NULL but it is not working. I'm filling it with on class Test: Other *a = new Other(1,1); Other *b = new Other(2,2); Other *c = new Other(3,3); v->push_back(a); v->push_back(b); v->push_back(c); And on my main file I have: Test t; (...) Other *pointer = t.vect->at(0); delete t.vect->at(0); t.vect->erase(t.vect->begin()); if (pointer == NULL) { cout << "Nothing here.."; } // Never enters here..

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  • im i doing this right or wrong using pointers in C

    - by Amandeep Singh Dhari
    i like to point out that i need some help with my home work, ok the lectuer gave us the idea of a program and we have to make it from bottom to top. got to have user to type in two set of string. pointers take in the value and then puts into a prototype i need to make a 3rd pointer that has the value of p1 and p2. like this p1 = asd, p2 = qwe and p3 = asdqwe #include "stdafx.h" #include <ctype.h> char *mystrcat(char*s1p, char*s2p); // Prototype char main(void) { char string1[80]; char string2[80]; printf("%s", "enter in your srting one "); gets_s(string1); printf("%s", "enter in your srting two "); gets_s(string2); *mystrcat(string1, string2); return 0; } char *mystrcat(char *s1p,char *s2p) { //char *string3; //char *string4; //string3 = s1p; //string4 = s2p; printf("whatever = %s%s\n", s1p, s2p); return 0; } this is the code that i made so far just need some help, thank guys in advance.

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  • C++ design question, container of instances and pointers

    - by Tom
    Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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