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• C++: Allocation of variables in a loop

  - by Rosarch

  Let's say I have a loop like this: vector<shared_ptr<someStruct>> vec; int i = 0; while (condition) { i++ shared_ptr<someStruct> sps(new someStruct()); WCHAR wchr[20]; memset(wchr, i, 20); sps->pwsz = wchr; vec.push_back(sps); } At the end of this loop, I see that for each sps element of the vector, sps->pwsz is the same. Is this because I'm passing a pointer to memory allocated in a loop, which is destructed after each iteration, and then refilling that same memory on the next iteration?

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• Strange C++ thread function invocation

  - by Tony

  I have the following: class DThread { virtual void run()=0; _beginthreadex(NULL,0,tfunc,this,0,&m_UIThreadID); // class itself being passed as param to thread function... static unsigned int __stdcall tfunc(void* thisptr) { static_cast<DThread*>(thisptr)->run(); return 0; } //other stuff } The run function is implemented in a derived class. Why is the function that's being called in the thread being called through a cast this pointer? Is this good practise? Can't it just be called directly? The actual function needing to run is in the derived class. My question is

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• Abstract class and operator!= in c++

  - by Alessandro Teruzzi

  Hi All, I have problem implementing the operator!= in a set class deriving from an abstact one. The code looks like this: class Abstract { public: //to make the syntax easier let's use a raw pointer virtual bool operator!=(const Abstract* other) = 0; }; class Implementation { SomeObject impl_; //that already implement the operator!= public: bool operator!=(const Abstract* other) { return dynamic_cast<Implementation*>(other)->impl_ != this->impl_; } }; This code works but it has the drawback to use dynamic_cast and I need to handle error in casting operation. This is a generic problem that occur when a function of a concrete class it is trying to using some internal information (not available at the abstract class level) to perform a task. Is there any better way to solve this kind of problem? Cheers

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• C++ Iterators and inheritance

  - by jomnis

  Have a quick question about what would be the best way to implement iterators in the following: Say I have a templated base class 'List' and two subclasses "ListImpl1" and "ListImpl2". The basic requirement of the base class is to be iterable i.e. I can do: for(List<T>::iterator it = list->begin(); it != list->end(); it++){ ... } I also want to allow iterator addition e.g.: for(List<T>::iterator it = list->begin()+5; it != list->end(); it++){ ... } So the problem is that the implementation of the iterator for ListImpl1 will be different to that for ListImpl2. I got around this by using a wrapper ListIterator containing a pointer to a ListIteratorImpl with subclasses ListIteratorImpl2 and ListIteratorImpl2, but it's all getting pretty messy, especially when you need to implement operator+ in the ListIterator. Any thoughts on a better design to get around these issues?

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• Help with implementing a function to change size of dynamic array

  - by iRobot

  I'm trying to write a function that will change the size of a dynamic array to a new size. In my header file, I have: Image **images; //pointer to a dynamic array of image pointers int maximum; //size I want to do this by allocating a new array and copying the values over without changing their indices. If there are non-null pointers outside the range newmax, then we cant do this. So heres what I have: There are no compilation or runtime errors. However, I find that the new array isnt getting sized right. When I run the following test case: I should get an index out of bounds error, but instead the system lets it slide. Can anyone see the mistake? I've looked for hours but cant find anything.

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• Break the limit of threading, segmentation fault

  - by user353573

  use pthread_create to create limited number of threads running concurrently Successfully compile and run However, after adding function pointer array to run the function, Segmentation fault Where is wrong? workserver number: 0 Segmentation fault void* workserver(void arg) { int status; while(true) { printf("workserver number: %d\n", (int)arg); ( job_queue[(int)arg])(); sleep(3); status = pthread_mutex_lock(&data.mutex); if(status != 0) printf("%d lock mutex", status); data.value = 1; status = pthread_cond_signal(&data.cond); if(status != 0) printf("%d signal condition", status); status = pthread_mutex_unlock(&data.mutex); if(status != 0) printf("%d unlock mutex", status); } }

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• question abouut string sort

  - by davit-datuashvili

  i have question from programming pearls problem is following show how to use lomuto's partitioning scheme to sort varying length bit strings in time proportional to the sum oof their length and algorithm is following each record in x[0..n-1] has an integer length and pointer to the array bit[0..length-1] code void bsort(l,u,depth){ if (l>=u) return; for (int i=l;i<u;i++) if (x[i].length<depth) swap(i,l++); m=l; if (x[i].bit[depth] ==0) swap(i,m++); bsort(l,m-1,depth+1); bsort(m,u,depth+1); please help me i need following things 1. how this algorith works 2.how implement in java?

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• Is it possible to deploy a Ruby app on a plain clean Passenger setup?

  - by Folletto

  I'm thinking to something really similar on what you can do with mod_php: drop an application in some way inside Apache and making it run with Passenger, without adding anything inside httpd.conf (no vhost, nothing except the basic Passenger configuration). It's something very similar to Wordpress or many other frameworks: just unzip/svn checkout it inside a folder and run it. I know that it's possible with CGI and FCGI, but I'm wondering if it's also possible to tap in the speed of Passenger. I've tried fiddling with the Rack instructions on the official website trying to find a specific .htaccess and config.ru configuration, but nothing so far. I know it's not common, but... is it even possible?

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• Are unspecified and undefined behavior required to be consistent between compiles?

  - by sharptooth

  Let's pretend my program contains a specific construct the C++ Standard states to be unspecified behavior. This basically means the implementation has to do something reasonable but is allowed not to document it. But is the implementation required to produce the same behavior every time it compiles a specific construct with unspecified behavior or is it allowed to produce different behavior in different compiles? What about undefined behavior? Let's pretend my program contains a construct that is UB according to the Standard. The implementation is allowed to exhibit any behavior. But can this behavior differ between compiles of the same program on the same compiler with same settings in the same environment? In other words, if I dereference a null pointer on line 78 in file X.cpp and the implementation formats the drive in such case does it mean that it will do the same after the program is recompiled?

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• Getting facts from documents

  - by dotnetdev

  Hi, I want to be able to get all the facts from webpages. But these have to be related to coding, and not, for example, about something irrelevant. For example: The Engine renders at a decent speed. May be a fact but is not what I am interested in. If the same article states: A class is a reference type. (This is C#) Then I am interested in that as it is coding related. Has an algorithm like this ever been done? How hard would this be? I'm thinking AI would come into play here. Any advice sought. Thanks

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• lambda+for_each+delete on STL containers

  - by rubenvb

  I'm trying to get a simple delete every pointer in my vector/list/... function written with an ultra cool lambda function. Mind you, I don't know c**p about those things :) template <typename T> void delete_clear(T const& cont) { for_each(T.begin(), T.end(), [](???){ ???->delete() } ); T.clear(); } I have no clue what to fill in for the ???'s. Any help is greatly appreciated!

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• Using GCC 4.2 to compile *.mm files is very very slow, but LLVM has done a very good job, any difference?

  - by jianhua

  My project is obj-c and C++ hybirid, filled with by both *.m and *.mm. When compiling, if choose GCC 4.2, *.m obj-c source files compile speed is very fast but *.mm very very slow, but LLVM 2.0 can do a very good job, it is very fast for both *.m and *.mm. My question: Is there any difference between LLVM and GCC 4.2 during compliling *.mm files? why GCC 3.2 is so slow? Any ieda or discussion will be appreciated, thanks in advance. ENV: XCODE 4.0.1

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• C++ operator[] syntax.

  - by Lanissum

  Just a quick syntax question. I'm writing a map class (for school). If I define the following operator overload: template<typename Key, typename Val> class Map {... Val* operator[](Key k); What happens when a user writes: Map<int,int> myMap; map[10] = 3; Doing something like that will only overwrite a temporary copy of the [null] pointer at Key k. Is it even possible to do: map[10] = 3; printf("%i\n", map[10]); with the same operator overload?

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• Is this possible?

  - by Stud33

  I want to incorporate some Accelerometer code into a Android application im working and want to see if this is possible. Basically what I need is for the code to detect car acceleration motion. I am not wanting to determine speed with the code but just distinguish if the phone is in a car and has accelerated motion (Hence the car is moving for the first time). I have gone through many different accelerometer applications to see if this motion produces a viable profile to go off of and it appears it does. Just looking for something that popups a "Hello World" dialog when it detects your in the car and its moving for the first time down the street. Any help would be appreciated and a simple yes or no its possible would work. I would also be interested in compensating anyone that is capable of doing this as well. I need this done like yesterday so please let me know. Thank You, JTW

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• speeding up parsing of files

  - by user248237

  the following function parses a CSV file into a list of dictionaries, where each element in the list is a dictionary where the values are indexed by the header of the file (assumed to be the first line.) this function is very very slow, taking ~6 seconds for a file that's relatively small (less than 30,000 lines.) how can I speed it up? def csv2dictlist_raw(filename, delimiter='\t'): f = open(filename) header_line = f.readline().strip() header_fields = header_line.split(delimiter) dictlist = [] # convert data to list of dictionaries for line in f: values = map(tryEval, line.strip().split(delimiter)) dictline = dict(zip(header_fields, values)) dictlist.append(dictline) return (dictlist, header_fields) thanks.

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• Artificial Intelligence Project - What language should I go for?

  - by Kremlin Yocepf

  Hi, I am a computer science student and I am going to work on an artificial intelligence project which will compose a musical tune according to the genre and mood inputs. Are the algorithms to be used for this project likely to be very resource-consuming? Would it make any difference (in terms of speed) if I choose to go with Java rather than C++? (Note : I know only these two languages and I am more comfortable with Java than C++.) NB : Sorry for my poor English. If someone can, please clean up this post wherever necessary. Thanks.

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• C++ syntax of constructors " 'Object1 a (1, Object1(2))''

  - by osgx

  Hello I have a such syntax in program class Object1 : BaseClass { BaseClass *link; int i; public: Object1(int a){i=a;} Object1(int a, Object1 /*place1*/ o) {i=a; link= &o;} }; int main(){ Object1 a(1, /*place2*/ Object1(2)); ... } What do I need in place1? I want to save a link (pointer) to the second object in the first object. Should I use in place1 reference "&"? What type will have "Object1(2)" in place2? Is it a constructor of the anonymous object? Will it have a "auto" storage type?

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• c++ - FIFO implementation

  - by Narek

  While implementing a FIFO I have used the following structure: struct Node { T info_; Node* link_; Node(T info, Node* link=0): info_(info), link_(link) {} }; I think this a well known trick for lots of STL containers (for example for List). Is this a good practice? What it means for compiler when you say that Node has a member with a type of it's pointer? Is this a kind of infinite loop? And finally, if this is a bad practice, how I could implement a better FIFO.

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• php vs python django or something else for CMS module

  - by Michael

  We're looking to develop a CMS module for our website and I need some help in choosing the language/framework for this project. Basically we need to develop a "help' module like this one from ebay http://pages.ebay.com/help/index.html which will contain a lot of static pages with nice URLs for SEO. The application must run fast using low computer resources. We have been looking to use php on a custom made mvc framework but we received advice from other sources that py/django is the exactly language/framework that we need in terms of maintainability and development speed because it was developed for exactly this kind of projects so I need an expert advice on this matter with pro and cons for each choice.

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• Input Iterator for a shared_ptr

  - by Baz

  I have an iterator which contains the following functions: ... T &operator*() { return *_i; } std::shared_ptr<T> operator->() { return _i; } private: std::shared_ptr<T> _i; ... How do I get a shared pointer to the internally stored _i? std::shared_ptr<Type> item = ??? Should I do: MyInterfaceIterator<Type> i; std::shared_ptr<Type> item = i.operator->(); Or should I rewrite operator*()?

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• question on revrse array

  - by davit-datuashvili

  we know algorithm how reverse array of n integers for (int i=0;i<n/2;i++){ swap(a[i],a[n-1-i]): } is this method better according the speed of algorithm or not because swap using xor is more fast then in other method here is code public class swap{ public static void main(String[]args){ int a[]=new int[]{2,4,5,7,8,11,13,12,14,24}; System.out.println(" array at the begining:"); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } for (int j=0;j<a.length/2;j++){ a[j]^=a[a.length-1-j]; a[a.length-1-j]^=a[j]; a[j]^=a[a.length-1-j]; } System.out.println("reversed array:"); for (int j=0;j<a.length;j++){ System.out.println(a[j]); } } } //result array at the begining: 2 4 5 7 8 11 13 12 14 24 reversed array: 24 14 12 13 11 8 7 5 4 2

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• Windows Phone 7 Control Caching - 'Element is already the child of another element'

  - by will

  I'm trying to speed up my windows phone 7 page load times. I have a 'static' page that has a dynamically created in a Panorama control - static meaning that the content never changes. On the first load I look at my config file, create the individual PanoramaItem controls and add them to the main Panorama control. I'm trying to keep a List in a static place so that the initial creation would only happen once and I could just add a fully rendered version to my Panorama control when the page was rendered. Works fine on first load, but when I try to add the cached PanoramaItems to the Panorama control I get the message "Element is already the child of another element". This makes sense since I already added before. But I can see a way to disconnect the PanoramaItems with the first Panorama control... I could be going about the control caching thing all wrong as well... Let me know if there's another way to do this.

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• C++ function call routes resolver

  - by Poni

  Hi! I'm looking for a tool that will tell/resolve for every function all the call paths (call it "routes") to it. For example: void deeper(int *pNumber) { *pNumber++; } void gateA(int *pNumber) { deeper(pNumber); } void gateB(int *pNumber) { gateA(pNumber); } void main() { int x = 123; gateA(&x); gateB(&x); } See? I need a tool that will tell me all the routes to deeper(), and more if possible. By saying "more" I mean that it will tell me if the pointer is the same as been provided to the calling function. This will greatly save me time. Thanks!

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• How to do hex8 encoding in c?

  - by Tech163

  I am trying to encode a string in hex8 using c. The script I have right now is: int hex8 (char str) { str = printf("%x", str); if(strlen(str) == 1) { return printf("%s", "0", str); } else { return str; } } In this function, I will need to add a 0 ahead of the string if the length is less than 1. I don't know why I'm getting: passing argument 1 of 'strlen' makes pointer from integer without a cast Does anyone know why?

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• memcpy does not copy the data

  - by user437777

  I am caught up with a weird problem. I have one build that copies data using memcpy, while another build does not. I don't understand why, because the relevant file is still the same. I am using following code: memcpy(pxCurrentInfo, &pxInfoBuffer->axgInfoBuffer[0], sizeof(tInfo)); Data in pxInfoBuffer is fine. When I check pxCurrentInfo they are all 0s. tInfo is a structure. To give a pointer, when I put the break point and change the value pxCurrentInfo->xDL.eMethod=0 it automatically updates/copies all the correct info from pxInfoBuffer->axgInfoBuffer[0], afterwards. I don't know why.

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