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• What does it mean to pass a &variable to a function? E.g., string& insert ( size_t pos1, const strin

  - by Bob Montgomery

  I understand passing a pointer, and returning a pointer: char * strcat ( char * destination, const char * source ); You're passing a variable that contains the address to a char; returning the same. But what does it mean to pass something using the reference operator? Or to return it? string& insert ( size_t pos1, const string& str ); I mean, I understand what actually happens, I just don't understand the notation. Why isn't the notation this instead: string * insert ( size_t pos1, const string * str ); //made up I presume it has something to do with passing/returning the instance of a class, but what? Is this syntax valid; if not why not and if so what does it mean? char & strcat ( char & destination, const char & source ); //made up (all of the function declarations, except the last made-up two, are from http://www.cplusplus.com )

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• Start a thread using a method pointer

  - by Michael

  Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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• Create thread is not accepting the member functon

  - by prabhakaran

  I am trying to create a class for network programming. This will create a general purpose socket with thread. But when I tried to creat the thread using createthread(). The third argument is producing errors. And from the net I came to know that I can't use the member functions as a argument to the createthread(). Is there any thing by which I can achieve this.

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• Void pointers in C

  - by avd

  I have written this qsort: void qsort(void *a[],int low,int high, int (*compare)(void*,void*)); When I call this on char *strarr[5]; It says invalid conversion from char** to void**. Why this is wrong? This is the code:http://codepad.org/Flfm2zAE

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• C++ Pointers, objects, etc

  - by Zeee

  It may be a bit confusing, but... Let's say I have a vector type in a class to store objects, something like vector, and I have methods on my class that will later return Operators from this vector. Now if any of my methods receives an Operator, will I have any trouble to insert it directly into the vector? Or should I use the copy constructor to create a new Operator and put this new one on the vector?

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• Access violation of member of pointer object

  - by Martin Lauridsen

  So I am coding this client/server program. This code is from the client side. The client has an instance of an object mpqs_sieve *instance_; The reason I make it as a pointer is, that mpqs_sieve only has a constructor that takes 3 arguments, and I want to instantiate it at a later point in time. The client first gets some data from the server, and uses this to instantiate instance_. After this, it will request some more data, and upon receiving this (these are three coeffecients for a quadratic polynomial), it should set these in the instance_ object. However upon calling a member function of instance_, I get an access violation on one of the members of instance_ within that function call. I posted my code here: on pastebin, and I get the error on line 100. The call comes from line 71, and before that line 21. Any ideas to solve this? Thanks!

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• Vector of pointers to base class, odd behaviour calling virtual functions

  - by Ink-Jet

  I have the following code #include <iostream> #include <vector> class Entity { public: virtual void func() = 0; }; class Monster : public Entity { public: void func(); }; void Monster::func() { std::cout << "I AM A MONSTER" << std::endl; } class Buddha : public Entity { public: void func(); }; void Buddha::func() { std::cout << "OHMM" << std::endl; } int main() { const int num = 5; // How many of each to make std::vector<Entity*> t; for(int i = 0; i < num; i++) { Monster m; Entity * e; e = &m; t.push_back(e); } for(int i = 0; i < num; i++) { Buddha b; Entity * e; e = &b; t.push_back(e); } for(int i = 0; i < t.size(); i++) { t[i]->func(); } return 0; } However, when I run it, instead of each class printing out its own message, they all print the "Buddha" message. I want each object to print its own message: Monsters print the monster message, Buddhas print the Buddha message. What have I done wrong?

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• array of pointers

  - by tushar

  char *a[]={"diamonds","clubs","spades","hearts"}; char **p[]={a+3,a+2,a+1,a}; char ***ptr=p; cout<<*ptr[2][2]; why does it display h and please explain how is the 2d array of ptr implementing and its elements

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• c# binarysearch a list<T> by a member of T

  - by Pygmy

  I have a baseclass Event with a DateTime member TimeStamp. Lots of other event-classes will derive from this. I want to be able to search a list of events (that can contain events with duplicate timestamps) fast, so I'd like to use a binary search. So I started out writing something like this : public class EventList<T> : List<T> where T : Event { private IComparer<T> comparer = (x, y) => Comparer<DateTime>.Default.Compare(x.TimeStamp, y.TimeStamp); public IEnumerable<T> EventsBetween(DateTime inFromTime, DateTime inToTime) { // Find the index for the beginning. int index = this.BinarySearch(inFromTime, comparer); // BLAH REST OF IMPLEMENTATION } } The problem is that the BinarySearch only accepts T (so - an Event type) as parameter, while I want to search based on a member of T - the TimeStamp. What would be a good way to approach this ?

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• Arrays of pointers to arrays?

  - by a2h

  I'm using a library which for one certain feature involves variables like so: extern const u8 foo[]; extern const u8 bar[]; I am not allowed to rename these variables in any way. However, I like to be able to access these variables through an array (or other similar method) so that I do not need to continually hardcode new instances of these variables into my main code. My first attempt at creating an array is as follows: const u8* pl[] = { &foo, &bar }; This gave me the error cannot convert 'const u8 (*)[]' to 'const u8*' in initialization, and with help elsewhere along with some Googling, I changed my array to this: u8 (*pl)[] = { &foo, &bar }; Upon compiling I now get the error scalar object 'pl' requires one element in initializer. Does anyone have any ideas on what I'm doing wrong? Thanks.

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• Accessing structure elements using pointers

  - by Arun Nadesh

  Hi Everybody, Greetings! I got surprised when the following program did not crash. typedef struct _x{ int a; char b; int c; }x; main() { x *ptr=0; char *d=&ptr->b; } As per my understanding the -> operator has higher precedence over & operator. So I expected the program to crash at the below statement when we try to dereference the NULL pointer tr. char *d=&ptr->b; But the statement &ptr->b evaluates to a valid address. Could somebody please explain where I'm wrong? Thanks & Regards, Arun

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• How to handle an array of pointers in Objective-C

  - by DougW

  I figured out the answer to this question, but I couldn't find the solution on here, so posting it for posterity. So, in Objective-C, how do you create an object out of a pointer in order to store it in objective-c collections (NSArray, NSDictionary, NSSet, etc) without reverting to regular C?

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• Help with pointers in Cocoa

  - by G.P. Burdell

  I'm trying to make a simple calculator application in cocoa. The program hangs when I click on one of my buttons. I think I've traced the problem to the part of my controller that adds a digit to the end of the number currently on the display: - (void)updateNumber:(int)buttonClicked{ *self.activeNumberPointer = *self.activeNumberPointer * 10 + buttonClicked; [outputField setFloatValue:*self.activeNumberPointer]; } I used a pointer to the "activeNumber" in order to allow my program to tell which of the two operands I'm editing. Any help appreciated, thanks.

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• COM Pointers and process termination

  - by Tony

  Can an unreleased COM pointer to an external process (still alive) cause that process to hang on destruction? Even with TerminateProcess called on it? Process A has a COM interface pointer reference to Process B, now Process B issues a TerminateProcess on A, if some COM interface pointer to Process B in Process A is not released properly, could it be that the process hangs on termination?

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• Pointers in C# to make int array?

  - by Joshua

  The following C++ program compiles and runs as expected: #include <stdio.h> int main(int argc, char* argv[]) { int* test = new int[10]; for (int i = 0; i < 10; i++) test[i] = i * 10; printf("%d \n", test[5]); // 50 printf("%d \n", 5[test]); // 50 return getchar(); } The closest C# simple example I could make for this question is: using System; class Program { unsafe static int Main(string[] args) { // error CS0029: Cannot implicitly convert type 'int[]' to 'int*' int* test = new int[10]; for (int i = 0; i < 10; i++) test[i] = i * 10; Console.WriteLine(test[5]); // 50 Console.WriteLine(5[test]); // Error return (int)Console.ReadKey().Key; } } So how do I make the pointer?

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• Vectors of Pointers, inheritance

  - by user308553

  Hi I am a C++ beginner just encountered a problem I don't know how to fix I have two class, this is the header file: class A { public: int i; A(int a); }; class B: public A { public: string str; B(int a, string b); }; then I want to create a vector in main which store either class A or class B vector<A*> vec; A objectOne(1); B objectTwo(2, "hi"); vec.push_back(&objectOne); vec.push_back(&objectTwo); cout << vec.at(1)->i; //this is fine cout << vec.at(1)->str; //ERROR here I am really confused, I checked sites and stuff but I just don't know how to fix it, please help thanks in advance

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• STL Vectors, pointers and classes

  - by anubis9

  Hey! Let's say i have 2 classes: class Class1 { public: std::vector<CustomClass3*> mVec; public: Class1(); ~Class1() { //iterate over all the members of the vector and delete the objects } }; class InitializerClass2 { private: Class1 * mPtrToClass1; public: InitializerClass2(); void Initialize() { mPtrToClass1->mVec.push_back(new CustomClass3(bla bla parameters)); } }; Will this work? Or the memory allocated in the InitializerClass2::Initialize() method might get corrupted after the method terminates? Thanks!

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• compilation error: request member in something not a structure of union

  - by Fantastic Fourier

  Hi everybody, I'm having the above error request member rv in something not a structure of union. I've googled it and several answers told me it's when working with a pointer but tries to access it as a struct, where I should be using -> instead of . int foo(void * arg, struct message * msg) { struct fd_info * info = (struct something *) arg; int * socks[MAX_CONNECTION]; socks = &(info->_socks); // where int * _socks[MAX_CONNECTION] in struct info // do other things rv = sendto(socks[i], &msg, sizeof(&msg), NULL, &(csys->client_address), sizeof(csys->client_address)); ... } The problem is all of the arguments i have are pointers. i'm confused as to what is wrong. thanks to any comments/thoughts.

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• An array of LPWSTR pointers, not working right.

  - by BigBirdy

  Declare: LPWSTR** lines= new LPWSTR*[totalLines]; then i set using: lines[totalLines]=&totalText; SetWindowText(totalChat,(LPWSTR)lines[totalLines]); totalLines++; Now I know totalText is right, cause if i SetWindowText using totalText it works fine. I need the text in totalLines too. I'm also doing: //accolating more memory. int orgSize=size; LPWSTR** tempArray; if (totalLines == size) { size *= 2; tempArray = new LPWSTR*[size]; memcpy(tempArray, lines,sizeof(LPWSTR)*orgSize); delete [] lines; lines = tempArray; } to allocate more memory when needed. My problem is that the lines is not getting the right data. It works for the first time around then it get corrupted. I thought at first i was overwriting but totalLines is increase. Hopefully this is enough information.

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• Copy constructor, objects, pointers

  - by Pauff

  Let's say I have this: SolutionSet(const SolutionSet &solutionSet) { this->capacity_ = solutionSet.capacity_; this->solutionsList_ = solutionSet.solutionsList_; // <-- } And solutionsList_ is a vector<SomeType*> vect*. What is the correct way to copy that vector (I suppose that way I'm not doing it right..)?

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• Problem with pointers

  - by noname

  OK, i have a strange problem. I have this piece of code: int *p; int test; p=&test; In Visual C++ express, in my exsisting project, I get this error: missing type specifier - int assumed. 'p' : 'int' differs in levels of indirection from 'char *' 'initializing' : cannot convert from 'char *' to 'int' But when i create new project, same code is fine. Whats the problem please?

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• Caching for a Custom Repositiory Adapter for WebSphere Portal Virtual Member Manager

  - by Spike Williams

  I'm looking at writing a custom repository adapter to interact with Virtual Member Manager on WebSphere Portal 6.1. Basically, its a layer that takes a request in the form of a commonj.sco.DataObject and passes that on to an external web service, to get various information on our logged in users that is not otherwise available in LDAP. I'm concerned about the performance hit of going to a service every time we want to pull some permission from the back end. My question is, can the Virtual Member Manager handle caching of data going in and out of the custom repository adapters, or is that something I'm going to have to build into the adapter myself?

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• c++ class member functions selected by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instatiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• c++ defining a static member of a template class with type inner class pointer

  - by Jack

  I have a template class like here (in a header) with a inner class and a static member of type pointer to inner class template <class t> class outer { class inner { int a; }; static inner *m; }; template <class t> outer <t>::inner *outer <t>::m; when i want to define that static member i says "error: expected constructor, destructor, or type conversion before '*' token" on the last line (mingw32-g++ 3.4.5)

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• Using pointers to adjust global objects in objective-c

  - by Rob

  Ok, so I am working with two sets of data that are extremely similar, and at the same time, these data sets are both global NSMutableArrays within the object. data_set_one = [[NSMutableArray alloc] init]; data_set_two = [[NSMutableArray alloc] init]; Two new NSMutableArrays are loaded, which need to be added to the old, existing data. These Arrays are also global. xml_dataset_one = [[NSMutableArray alloc] init]; xml_dataset_two = [[NSMutableArray alloc] init]; To reduce code duplication (and because these data sets are so similar) I wrote a void method within the class to handle the data combination process for both Arrays: -(void)constructData:(NSMutableArray *)data fromDownloadArray:(NSMutableArray *)down withMatchSelector:(NSString *)sel_str Now, I have a decent understanding of object oriented programming, so I was thinking that if I were to invoke the method with the global Arrays in the data like so... [self constructData:data_set_one fromDownloadArray:xml_dataset_one withMatchSelector:@"id"]; Then the global NSMutableArrays (data_set_one) would reflect the changes that happen to "array" within the method. Sadly, this is not the case, data_set_one doesn't reflect the changes (ex: new objects within the Array) outside of the method. Here is a code snippet of the problem // data_set_one is empty // xml_dataset_one has a few objects [constructData:(NSMutableArray *)data_set_one fromDownloadArray:(NSMutableArray *)xml_dataset_one withMatchSelector:(NSString *)@"id"]; // data_set_one should now be xml_dataset_one, but when echoed to screen, it appears to remain empty And here is the gist of the code for the method, any help is appreciated. -(void)constructData:(NSMutableArray *)data fromDownloadArray:(NSMutableArray *)down withMatchSelector:(NSString *)sel_str { if ([data count] == 0) { data = down; // set data equal to downloaded data } else if ([down count] == 0) { // download yields no results, do nothing } else { // combine the two arrays here } } This project is not ARC enabled. Thanks for the help guys! Rob

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