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• C++ vector reference parameter

  - by Archanimus

  Hello folks, let's say we have a class class MyClass { vector<vector<int > > myMatrice; public : MyClass(vector<vector<int > > &); } MyClass::MyClass(vector<vector<int > > & m) { myMatrice = m; } During the instanciation of MyClass, I pass a big vector < vector < int and I find that the object is actually copied and not only the reference, so it takes the double of the memory ... Please, can anyone help me out with this problem, I'm stuck since too many time ... And thanks a lot!

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• freeing malloc and checkin it is empty or not

  - by gcc

  char *p; p="kjkjk"; . .//there are codes which are checking another command . if(.....)//i used pointer p in only that area free(p); . . //there are codes which are checking another command . if(p==NULL) //i check whether is empty .... if(p==-1) //can we use "EOF==p " in if statement ... //are there any usage like that EOF==p else .... I think there is big error , but where?

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• Can I reproduce Scala's behavior for == ?

  - by JPP

  In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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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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• 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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• Speedup C++ code

  - by Werner

  Hi, I am writing a C++ number crunching application, where the bottleneck is a function that has to calculate for double: template<class T> inline T sqr(const T& x){return x*x;} and another one that calculates Base dist2(const Point& p) const { return sqr(x-p.x) + sqr(y-p.y) + sqr(z-p.z); } These operations take 80% of the computation time. I wonder if you can suggest approaches to make it faster, even if there is some sort of accuracy loss Thanks

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• A generic list of generics

  - by SnOrfus

  I'm trying to store a list of generic objects in a generic list, but I'm having difficulty declaring it. My object looks like: public class Field<T> { public string Name { get; set; } public string Description { get; set; } public T Value { get; set; } /* ... */ } I'd like to create a list of these. My problem is that each object in the list can have a separate type, so that the populated list could contain something like this: { Field<DateTime>, Field<int>, Field<double>, Field<DateTime> } So how do I declare that? List<Field<?>> (I'd like to stay as typesafe as possible, so I don't want to use an ArrayList).

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• What is the difference between these two ways of creating NSStrings?

  - by adame

  NSString *myString = @"Hello"; NSString *myString = [NSString stringWithString:@"Hello"]; I understand that using method (1) creates a pointer to a string literal that is defined as static memory (and cannot be deallocated) and that using (2) creates an NSString object that will be autoreleased. Is using method (1) bad? What are the major differences? Is there any instances where you would want to use (1)? Is there a performance difference? P.S. I have searched extensively on Stack Overflow and while there are questions on the same topic, none of them have answers to the questions I have posted above.

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• I am looking for a svn helper program

  - by uzay95

  I didn't remember the name of this program. But i can remember how it works. Program is working on tray. When we double click on it it is showing its main window. :) I could add some criterias to make automatic commit(and maybe update). For ex: if a file changes or if files to be deleted, you can commit. The best part of this program is: "it is FREE" I don't remember exactly but i think it has M name in its name (but i don't remember). I think this program written by an Italian man. And its web site was very simple (and i think its fonts were green)

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• Need guidance for my first Android application: how many activities should I use?

  - by jul

  Hi, I'm starting Android doing an application for searching restaurants, and some guidance would be welcome! On the first screen I'd like to have a search field with a submit button (I get the data from a web service), and below a list with the results of the search. When clicking on one of the items of the list it will show a screen with the restaurant details as well as a map showing its location. My questions are: Can I do everything in one single activity or should I do an activity for the search, one for the result list, one for the restaurant description, and another for the map? Would doing one single activity make the application more responsive? How can I use a list and a map within a normal activity (without ListActivity and MapActivity)? Any help, pointer, example application or sample code is very appreciated! Thank you Jul

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• Both sql LAST_INSERT_ID() and PHP insert_id return 0

  - by jakubplus

  I've been searching google a lot for this issue and really found nothing. People just keep copying MySQL documentation on last_insert_id and nothing else. I've got an issue regarding last_insert_id, because for both situations (php & sql) it returns 0. YES: I've set a PRIMARY & UNIQUE field with AUTO_INCREMENT value YES: i've done some inserting before NO: Making double query with INSERT AND SELECT LAST... doesn't work. I've created a class Db for maintaining connection & query: class Db { public function connect() { $db = new mysqli('','','','',''); ... return $db; } public function insert() { $this->connect()->query("INSERT INTO bla bla..."); return $this->connect()->insert_id; } } And it doesn't work.

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• Can a real number "cover" all integers within its range?

  - by macias

  Is there a guarantee that a real number (float, double, etc) can "cover" all integers within its range? By cover I mean, that for every integer within its range there is such real number that this equality holds: real == int Or in another example, let's say I have the biggest real number which is smaller than given integer. When I add "epsilon" will I get this number equal to given integer or bigger than integer? (I know that among real numbers you should not write comparisons as == for equality, I am simply asking for better understanding subject, not for coding comparisons.)

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• Best way to access nested data structures?

  - by Blackshark

  I would like to know what the best way (performance wise) to access a large data structure is. There are about hundred ways to do it but what is the most accessible for the compiler to optimize? One can access a value by foo[someindex].bar[indexlist[i].subelement[j]].baz[0] or create some pointer aliases like sometype_t* tmpfoo = &foo[someindex]; tmpfoo->bar[indexlist[i].subelement[j]].baz[0] or create reference aliases like sometype_t &tmpfoo = foo[someindex]; tmpfoo.bar[indexlist[i].subelement[j]].baz[0] and so forth...

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• C++ Vector of vectors

  - by xbonez

  I have a class header file called Grid.h that contains the following 2 private data object: vector<int> column; vector<vector<int>> row; And a public method whose prototype in Grid.h is such: int getElement (unsigned int& col, unsigned int& row); The definition of above mentioned function is defined as such in Grid.cpp: int getElement (unsigned int& col, unsigned int& row) { return row[row][col] ; } When I run the program, I get this error: error C2109: subscript requires array or pointer type Whats going wrong?

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• A little javascript help needed here (easy).

  - by Camran

  function addOption(selectbox, val, txt){ ...... } addOption(list, "Cars", "Cars"); I need to add this in front of the text of the function: &nbsp;&nbsp;&nbsp; So that there is space coming in before the option text...Never mind what it is for, it is just confusing... I just don't know how to insert it into the js code. If I do it like this: addOption(list, "Cars", "&nbsp;&nbsp;&nbsp;Cars"); Then the &nbsp;&nbsp;&nbsp; comes into the text, so it gets displayed for the users. However I need it to be interpreted as "space"... If you don't understand let me know... How can I do this? Quotes, double quotes etc? 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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• visual studio C++ toggle comment ? comment while not whole line is selected ?

  - by Mr_and_Mrs_D

  2 questions actually : 1) shortcut to toggle comment on selected lines ? Available on all iDEs I used starting with notepad++ 2)the ctrl-k, ctrl-c exhibits this behavior (quoted from someplace nicely worded): C#: Each line where some text is selected is commented at the line-start with double-slash. If nothing is selected, the line where the cursor is is commented. C++: If nothing is selected or complete lines are selected, it behaves as above. However, if parts of a line are selected, and no comment is selected as part of the selection (ex. select something in the middle of a code line), then the selection is surrounded by /* and */. since I code in C++ I find this behavior annoying - I want to be able to comment out lines partially selected - any workarounds ?

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• Memory allocated with malloc does not persist outside function scope?

  - by PM

  Hi, I'm a bit new to C's malloc function, but from what I know it should store the value in the heap, so you can reference it with a pointer from outside the original scope. I created a test program that is supposed to do this but I keep getting the value 0, after running the program. What am I doing wrong? int f1(int * b) { b = malloc(sizeof(int)); *b = 5; } int main() { int * a; f1(a); printf("%d\n", a); return 0; }

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• CUDA Global Memory, Where is it?

  - by gamerx

  I understand that in CUDA's memory hierachy, we have things like shared memory, texture memory, constant memory, registers and of course the global memory which we allocate using cudaMalloc(). I've been searching through whatever documentations I can find but I have yet to come across any that explicitly explains what is the global memory. I believe that the global memory allocated is on the GDDR of graphics card itself and not the RAM that is shared with the CPU since one of the documentations did state that the pointer cannot be dereferenced by the host side. Am I right?

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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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• How does the stream manipulators work?

  - by Narek

  It is well known that the user can define stream manipulators like this: ostream& tab(ostream & output) { return output<< '\t'; } And this can be used in main() like this: cout<<'a'<<tab<<'b'<<'c'<<endl; Please explain me how does this all work? If operator<< assumes as a second parameter a pointer to the function that takes and returns ostream &, then please explain my why it is necessary? What would be wrong if the function does not take and return ostream & but it was void instead of ostream &? Also it is interesting why “dec”, “hex” manipulators take effect until I don’t change between them, but user defined manipulators should be always used in order to take effect for each streaming?

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• looping and arrays

  - by user1838418

  Hi I'm trying to construct a loop to execute 16 states of the 8 4 2 1 code in (C++) while( condition) { double Bubble[16], Bubble1[16]; Bubble[0] = ( a-2 - (b-2) ) + ( c-2 - (d-2)); // represents 0000 Bubble[1] = ( a-2 - (b-2) ) + ( c-2 - (d+2)); // represents 0001 Bubble[2] = ( a-2 - (b-2) ) + ( c+2 - (d-2)); // represents 0010 Bubble[3] = ( a-2 - (b-2) ) + ( c+2 - (d+2)); //represents 0011 ....... Bubble[15] =(a+2 - (b+2) ) + ( c+2 - (d+2)); //represents 1111 } Is there an easy way of coding using for loops? instead of writing bubble[] every time? 0 stands for -2 and 1 stands for +2. So I have 4 variables and each one need to be incremented and/or decremented. Can this be done using for loop? Appreciate your help

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• strategy to allocate/free lots of small objects

  - by aaa

  hello I am toying with certain caching algorithm, which is challenging somewhat. Basically, it needs to allocate lots of small objects (double arrays, < 256 elements), with objects accessible through mapped value, map[key] = array. time to initialized array may be quite large, generally more than 10 thousand cpu cycles. By lots I mean around gigabyte in total. objects may need to be popped/pushed as needed, generally in random places, one object at a time. lifetime of an object is generally long, minutes or more, however, object may be subject to allocation/deallocation several times during duration of program. What would be good strategy to avoid memory fragmentation, while still maintaining reasonable allocate deallocate speed? I am using C++, so I can use new and malloc. Thanks. I know there a similar questions on website, http://stackoverflow.com/questions/2156745/efficiently-allocating-many-short-lived-small-objects, are somewhat different, thread safety is not immediate issue for me.

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• TPageControl tab area OnMouseEnter OnMouseLeave events

  - by daemon_x

  Hello, I need to catch the "OnMouseEnter" and "0nMouseLeave" for a certain area of the TPageControl component. With that specific area I mean the whole "tab header" rectangle. The problem is, that the page control doesn't catch the messages (I'm catching internal control messages CM_MOUSEENTER and CM_MOUSELEAVE) in the "empty" space. The aim for me is to draw a small arrow in the right empty side when user hovers in the red framed area (and drawing is just piece of cake) and erase it when leaves this area. And I'm don't care about the overflow of the tabs (which causes to draw scrolling double button) - that will never happen.

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• Layout of popup components changes while moving

  - by Le_Coeur

  I have designed some popup moving menu with JQuery, it looks perfekt in webkit browsers, but i have one problem in mozilla, when i move my popup window, layout of some components in this window changes! For example button add changes from: to: or to: , and it's absolutly random. What can it be? This image is in span: <span class="sw_link_add"></span> .sw_link_add { background:url("/img/confirm_new.png") no-repeat scroll right center transparent; cursor:pointer; padding-right:30px; padding-top:2px; }

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