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• How to check if TypeIdenitifier(T) is an Object?

  - by John

  I'm creating a generic list class that has a member of type Array(Array of ). The problem is the class descruction,because the class is supposed to be used for types from byte to types inheriting TObject. Specifically: destructor Destroy; var elem:T; begin /*if(T is Tobject) then //Check if T inherits TObject {Compiler error!} for elem in FData do TObject(elem).Free;*/ // do not know how to do it SetLength(FItems,0); //FItems : Array of T inherited Destroy; end; How do I check if T is TObject so I can free every member if the typeidenitifier is a class,for example?

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• Same memory space being allocated again & again while using malloc()

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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• Reference to an instance method of a particular object

  - by Andrey

  In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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• Cast vector<T> to vector<const T>

  - by user345386

  I have a member variable of type vector (where is T is a custom class, but it could be int as well.) I have a function from which I want to return a pointer to this vector, but I don't want the caller to be able to change the vector or it's items. So I want the return type to be const vector* None of the casting methods I tried worked. The compiler keeps complaining that T is not compatible with const T. Here's some code that demonstrates the gist of what I'm trying to do; vector<int> a; const vector<const int>* b = (const vector<const int>* ) (&a); This code doesn't compile for me. Thanks in advance!

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• How to know record has been updated successfully in php

  - by Lisa Ray

  $sql = "UPDATE...."; if(mysql_query($sql)) { $_SESSION['Trans']="COMMIT"; header("location:result.php"); exit; } else { $_SESSION['Trans']="FAIL"; $_SESSION['errors'] = "Error: Sorry! We are unable to update your Profile, Please contact to PNP HelpDesk."; header("location:result.php"); exit; }//end IF data is getting updated then why compiler is not coming inside IF condition.

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• Why I have to redeclare a virtual function while overriding [C++]

  - by Neeraj

  #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

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• Why does C++ linking use virtually no CPU? (updated)

  - by John

  On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no? update: so the obvious follow-up is, can VC++ compiler and linker talk together better to streamline things and keep OBJ files in memory, similar to how Delphi does?

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• iOS sdk question: how do I cast a UIView to a UIImage View (alternativly how do I get a UIImageView from a GestureRecognzer?)

  - by user439299

  Desired end result: user taps a UIImageView and the image changes to another image (a subsequent tap returns the image to the original state) Problem: I add a (unique) selector to a bunch of UIImageViews (in an array) and point the action at the same function - let's call this function imageTapped: for now. Here is my code so far: -(void)imageTapped:(UITapGestureRecognizer *)tapGesture { UIImageView *view = tapGesture.view; // rest of code... } This code actually works fine but gets a warning when I run it: "Incompatible objective c types initilizing 'struct UIView *', expected 'struct UIImageView *' Any way to get rid of this? Not sure how casting works in objective c... primitive types seem to work fine such as (int)someFloat works fine but (UIImageView)someUiView doesn't work. Like I said, code works alright when I run it but would like to get ride of the compiler warning. Any help would be awesome.... I am very new to objective c (or any non java language for that matter) so be gentle. Thanks in advance.

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• Can I add a custom method to Core Data-generated classes?

  - by Andy

  I've got a couple of Core Data-generated class files that I'd like to add custom methods to. I don't need to add any instance variables. How can I do this? I tried adding a category of methods: // ContactMethods.h (my category on Core Data-generated "Contact" class) #import "Contact.h" @interface Contact (ContactMethods) -(NSString*)displayName; @end ... // ContactMethods.m #import "ContactMethods.h" @implementation Contact (ContactMethods) -(NSString*)displayName { return @"Some Name"; // this is test code } @end This doesn't work, though. I get a compiler message that "-NSManagedObject may not respond to 'displayName' " and sure enough, when I run the app, I don't get "Some Name" where I should be seeing it.

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• How to call C++ function from C?

  - by claws

  I know this. Calling C function from C++: If my application was in C++ and I had to call functions from a library written in C. Then I would have used //main.cpp extern "C" void C_library_function(int x, int y);//prototype C_library_function(2,4);// directly using it. This wouldn't mangle the name C_library_function and linker would find the same name in its input *.lib files and problem is solved. Calling C++ function from C??? But here I'm extending a large application which is written in C and I need to use a library which is written in C++. Name mangling of C++ is causing trouble here. Linker is complaining about the unresolved symbols. Well I cannot use C++ compiler over my C project because thats breaking lot of other stuff. What is the way out? By the way I'm using MSVC

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• Same memory space being allocated again & again

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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• Assigning Value to a variable that is too big for it! (checked and unchecked concept)

  - by ThickBook

  So when we assign a value to a variable then that variable should be able to hold it, right? and if not compiler produces the error. Now there is an option in C# known as Checked (which is by default) and unchecked option. But is there practical use of unchecked? any comments for a layman? :) Example: int a=int.MaxValue; int b=int.MaxValue; unchecked { int sum=a+b; }

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• Create object of unknown class (two inherited classes)

  - by Paul

  I've got the following classes: class A { void commonFunction() = 0; } class Aa: public A { //Some stuff... } class Ab: public A { //Some stuff... } Depending on user input I want to create an object of either Aa or Ab. My imidiate thought was this: A object; if (/*Test*/) { Aa object; } else { Ab object; } But the compiler gives me: error: cannot declare variable ‘object’ to be of abstract type ‘A’ because the following virtual functions are pure within ‘A’: //The functions... Is there a good way to solve this?

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• Heap Algorithmic Issue

  - by OberynMarDELL

  I am having this algorithmic problem that I want to discuss about. Its not about find a solution but about optimization in terms of runtime. So here it is: Suppose we have a race court of Length L and a total of N cars that participate on the race. The race rules are simple. Once a car overtakes an other car the second car is eliminated from the race. The race ends when no more overtakes are possible to happen. The tricky part is that the k'th car has a starting point x[k] and a velocity v[k]. The points are given in an ascending order, but the velocities may differ. What I've done so far: Given that a car can get overtaken only by its previous, I calculated the time that it takes for each car to reach its next one t = (x[i] - x[i+1])/(v[i] - v[i+1]) and I insert these times onto a min heap in O(n log n). So in theory I have to pop the first element in O(logn), find its previous, pop it as well , update its time and insert it in the heap once more, much like a priority queue. My main problem is how I can access specific points of a heap in O(log n) or faster in order to keep the complexity in O(n log n) levels. This program should be written on Haskell so I would like to keep things simple as far as possible EDIT: I Forgot to write the actual point of the race. The goal is to find the order in which cars exit the game

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• const member functions can call const member functions only?

  - by Abhi

  Hi all. Do const member functions call only const member functions? class Transmitter{ const static string msg; mutable int size; public: void xmit() const{ size = compute(); cout<<msg; } private: int compute() const{return 5;} }; string const Transmitter::msg = "beep"; int main(){ Transmitter t; t.xmit(); return EXIT_SUCCESS; } If i dont make compute() a const, then the compiler complains. Is it because since a const member function is not allowed to modify members, it wont allow any calls to non-consts since it would mean that the const member function would be 'indirectly' modifying the data members?

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• Quickly generate junk data of certain size in Javascript

  - by user1357607

  I am writing an upload speed test in Javascript. I am using Jquery (and Ajax) to send chunks of data to a server in order to time how long it takes to get a response. This should, in theory give an estimation, of the upload speed. Of course to cater for different bandwidths of the user I sequentially upload larger and larger amounts of junk data until a threshold duration is reached. Currently I generate the junk data using the following function, however, it is very slow when generation megabytes of data. function generate_random_data(size){ var chars = "abcdefghijklmnopqrstuvwxyz"; var random_data = ""; for (var i = 0; i < size; i++){ var random_num = Math.floor(Math.random() * char.length); random_data = random_data + chars.substring(random_num,random_num+1); } return random_data; Really all I am doing is generating a chunk of bytes to send to the server, however, this is the only way I could find out how in Javascript. Any help would be appreciated.

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• Operations on 64bit words in 32bit system

  - by Vilo

  I'm new here same as I'm new with assembly. I hope that you can help me to start. I'm using 32bit (i686) Ubuntu to make programs in assembly, using gcc compiler. I know that general-purpose-registers are 32bit (4 bytes) max, but what when I have to operate on 64 bit numbers? Intel's instruction says that higher bits are stored in %edx and lower in %eax Great... So how can I do something with this 2-registers number? I have to convert 64bit dec to bin, then save it to memory and show on the screen. How to make the 64bit quadword at start of the program in .data section?

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• Whats the difference between a C++ and a Cocoa Project in Xcode?

  - by david

  I need to work with TagLib for my project. I've created a framework (and I tried using it as a lib) but the compiler cannot find #include < strings on compiling (No such file or Directory). I've created a test C++ project and it #includes < strings just fine. I've looked at the project settings and I cannot find a difference between them. But the standard cocoa projects obviously so not have the search path set to include C++ libraries (Or am I completely getting it wrong?). I've searched for a solution but no one else seems to have run into this problem.

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• Normal C++ code in Qt doesnt build and run

  - by Nick

  Hello. I am using Qt under linux, if it matters. I ran successfully under Geany (a simple c++ compiler) the following: //my first program in C++ Hello World! include using namespace std; int main () {cout << "Hello World!"; return 0;} I opened Qt source file and copied the exact same code and i can't build or run. Thank you for your responses to this simple problem.

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• Need help making a div appear on the bottom of the screen while the rest of the divs scroll

  - by user1896600

  It's hard to describe my specific problem without just showing you the HTML code. The HTML source can be seen easily from clicking "View Source" while seeing the page http://techdot.us/projects/jeopardy/view.php. The CSS is located here: http://techdot.us/projects/jeopardy/style/gameStyle.css. My main goal is to have the main content table rows/columns appear on the majority of the screen (everything except 69px, to be exact). So, the bottom 69px contains an informational panel that is supposed to stay on the bottom of the screen, even when the user scrolls down the page. Scrolling is supposed to, in theory, trigger the majority of the content to go down the page normally, except the bottom bar which stays static. I have achieved this effect on the website. However, there is a big problem. On smaller screens (as you can simulate by resizing the window), some of the main table gets cut off. It seems that my CSS solution is a botch, and, in effect, does not accomplish my main goal. The bottom bar should not cut off part of the table from the main content div (gameTable), but the main content div should display all of its content in a scrollable fashion. My CSS at the moment works as long as the viewer's screen is a certain pixel height. This is definitely not permanent. Thank you SO much for the help. I really appreciate it and totally understand that I'm being a total pain by just throwing down tons of CSS and HTML code to edit.

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• cygwin g++ produces no output

  - by fred basset

  I just installed g++ from cygwin, when I try to compile a C++ file I am not getting any executable produced by the compiler, see example below. What's going wrong? Directory of C:\helloworld 01/02/2011 04:50 PM . 01/02/2011 04:50 PM .. 01/02/2011 04:48 PM 94 helloworld.cpp 1 File(s) 94 bytes 2 Dir(s) 24,658,272,256 bytes free C:\helloworldg++-4 helloworld.cpp C:\helloworlddir Volume in drive C is OS Volume Serial Number is C47B-942D Directory of C:\helloworld 01/02/2011 04:50 PM . 01/02/2011 04:50 PM .. 01/02/2011 04:48 PM 94 helloworld.cpp 1 File(s) 94 bytes 2 Dir(s) 24,657,747,968 bytes free C:\helloworld

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• How do I replace "this" in Java with something that works.

  - by Luke Alderton

  I'm looking to get the showGUI() method work, the compiler says "this" is not a static variable and cannot be referenced from a static context, what would I use to replace "this"? I've tried test.main (test being the package it's in). The reason I'm using the static method showGUI() is because I need the method to be called from another static method, as well as the startup() method. Below are my two main classes. public class Main extends SingleFrameApplication { @Override protected void startup() { showGUI(); } @Override protected void configureWindow(java.awt.Window root) { } public static Main getApplication() { return Application.getInstance(Main.class); } public static void main(String[] args) { launch(Main.class, args); } public static void showGUI() { show(new GUI(this)); } } public class GUI extends FrameView { public GUI(SingleFrameApplication app) { super(app); initComponents(); } private void initComponents() { //all the GUI stuff is somehow defined here } }

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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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• Class basic operators

  - by swan

  Hi, Is it necessary to have a copy constructor, destructor and operator= in a class that have only static data member, no pointer class myClass{ int dm; public: myClass(){ dm = 1; } ~myClass(){ } // Is this line usefull ? myClass(const myClass& myObj){ // and that operator? this->dm = myObj.dm; } myClass& operator=(const myClass& myObj){ // and that one? if(this != &myObj){ this->dm = myObj.dm; } return *this; } }; I read that the compiler build one for us, so it is better to not have one (when we add a data member we have to update the operators)

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• how to use replace_regex_copy() from boost::algorithm library?

  - by Vincenzo

  This is my code: #include <string> #include <boost/algorithm/string/regex.hpp> string f(const string& s) { using namespace boost::algorithm; return replace_regex_copy(s, "\\w", "?"); } This is what compiler says: no matching function for call to ‘replace_regex_copy(const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::string, std::string) The link to the library: http://www.boost.org/doc/libs/1_43_0/doc/html/boost/algorithm/replace_regex_copy.html Could anyone please help? Thanks! ps. Boost library is in place, since other functions from it work fine.

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