Search Results

Search found 9889 results on 396 pages for 'behind the compiler'.

Page 342/396 | < Previous Page | 338 339 340 341 342 343 344 345 346 347 348 349  | Next Page >

• What does an object look like in memory?

  - by NeilMonday

  This is probably a really dumb question, but I will ask anyway. I am curious what an object looks like in memory. Obviously it would have to have all of its member data in it. I assume that functions for an object would not be duplicated in memory (or maybe I am wrong?). It would seem wasteful to have 999 objects in memory all with the same function defined over and over. If there is only 1 function in memory for all 999 objects, then how does each function know who's member data to modify (I specifically want to know at the low level). Is there an object pointer that gets sent to the function behind the scenes? Perhaps it is different for every compiler? Also, how does the static keyword affect this? With static member data, I would think that all 999 objects would use the exact same memory location for their static member data. Where does this get stored? Static functions I guess would also just be one place in memory, and would not have to interact with instantiated objects, which I think I understand.

  Read the article

• JLabel transparency problem

  - by Rendicahya

  I have a dark-gray JPanel with a JLabel on it. I set new Color(0, 0, 0, .5f) (tranparent) as the background of the JLabel and I change the text several times using a button. The problem is, everytime the text is changed, the previous text still remains behind the new text. I change the text from "123456789" to "1234567", "12345" and "123". Here is the screenshot: How do I get rid of this "shadow"? Here's the code: public class TransparentJLabel extends JFrame { private int i = 0; private String[] value = {"123456789", "1234567", "12345", "123", "1"}; public TransparentJLabel() { setSize(300, 160); setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); setLayout(null); JPanel panel = new JPanel(); panel.setBackground(new Color(102, 102, 102)); panel.setLayout(null); panel.setBounds(0, 0, 300, 160); final JLabel label = new JLabel(); label.setText(value[0]); label.setFont(new Font("Times New Roman", 1, 36)); label.setForeground(new Color(255, 255, 255)); label.setBackground(new Color(0, 0, 0, .5f)); label.setHorizontalAlignment(SwingConstants.CENTER); label.setOpaque(true); label.setBounds(10, 10, 270, 70); JButton button = new JButton(); button.setText("Change"); button.setBounds(100, 90, 90, 25); button.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { label.setText(value[++i]); } }); panel.add(label); panel.add(button); add(panel); } public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { public void run() { new TransparentJLabel().setVisible(true); } }); } }

  Read the article

• Generics in a bidirectional association

  - by Verhoevenv

  Let's say I have two classes A and B, with B a subtype of A. This is only part of a richer type hierarchy, obviously, but I don't think that's relevant. Assume A is the root of the hierarchy. There is a collection class C that keeps track of a list of A's. However, I want to make C generic, so that it is possible to make an instance that only keeps B's and won't accept A's. class A(val c: C[A]) { c.addEntry(this) } class B(c: C[A]) extends A(c) class C[T <: A]{ val entries = new ArrayBuffer[T]() def addEntry(e: T) { entries += e } } object Generic { def main(args : Array[String]) { val c = new C[B]() new B(c) } } The code above obviously give the error 'type mismatch: found C[B], required C[A]' on the new B(c) line. I'm not sure how this can be fixed. It's not possible to make C covariant in T (like C[+T <: A]) because the ArrayBuffer is non-variantly typed in T. It's not possible to make the constructor of B require a C[B] because C can't be covariant. Am I barking up the wrong tree here? I'm a complete Scala newbie, so any ideas and tips might be helpful. Thank you! EDIT: Basically, what I'd like to have is that the compiler accepts both val c = new C[B]() new B(c) and val c = new C[A]() new B(c) but would reject val c = new C[B]() new A(c) It's probably possible to relax the typing of the ArrayBuffer in C to be A instead of T, and thus in the addEntry method as well, if that helps.

  Read the article

• C++ templates error: instantiated from 'void TestClass::testMethod(T, std::map) [with T = SomeClass]

  - by pureconsciousness

  Hello there, I've some problem in my code I cannot deal with: #ifndef TESTCLASS_H_ #define TESTCLASS_H_' #include <map> using namespace std; template <typename T> class TestClass { public: TestClass(){}; virtual ~TestClass(){}; void testMethod(T b,std::map<T,int> m); }; template <typename T> void TestClass`<T`>::testMethod(T b,std::map<T,int> m){ m[b]=0; } #endif /*TESTCLASS_H_*/ int main(int argc, char* argv[]) { SomeClass s; TestClass<SomeClass> t; map<SomeClass,int> m; t.testMethod(s,m); } Compiler gives me following error in line m[b]=0; : instantiated from 'void TestClass::testMethod(T, std::map) [with T = SomeClass] Could you help find the problem?? Thanks in advance

  Read the article

• how to install a file handle in perl class

  - by Haiyuan Zhang

  please looku up the following code first. #! /usr/bin/perl package foo; sub new { my $pkg = shift; my $self = {}; my $self->{_fd} = undef; bless $self, $pkg; return $self; } sub Setfd { my $self = shift; my $fd = shift; $self_->{_fd} = $fd; } sub write { my $self = shift; print $self->{_fd} "hello word"; } my $foo = new foo; My intention is to store a file handle within a class using hash. the file handle is undefined at first, but can be initilized afterwards by calling Setfd function. then write can be called to actually write string "hello word" to a file indicated by the file handle, supposed that the file handle is the result of a success "write" open. but, perl compiler just complains that there are syntax error in the "print" line. can anyone of you tells me what's wrong here? thanks in advance.

  Read the article

• variables in abstract classes C++

  - by wyatt

  I have an abstract class CommandPath, and a number of derived classes as below: class CommandPath { public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { int stage; public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; All of the derived classes have the member variable 'stage'. I want to build a function into all of them which manipulates 'stage' in the same way, so rather than defining it many times I thought I'd build it into the parent class. I moved 'stage' from the private sections of all of the derived classes into the protected section of CommandPath, and added the function as follows: class CommandPath { protected: int stage; public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; std::string confirmCommand(std::string, int, int, std::string, std::string); virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; Now my compiler tells me for the constructor lines that none of the derived classes have a member 'stage'. I was under the impression that protected members are visible to derived classes? The constructor is the same in all classes, so I suppose I could move it to the parent class, but I'm more concerned about finding out why the derived classes aren't able to access the variable. Also, since previously I've only used the parent class for pure virtual functions, I wanted to confirm that this is the way to go about adding a function to be inherited by all derived classes.

  Read the article

• Syntax for finding structs in multisets - C++

  - by Sarah

  I can't seem to figure out the syntax for finding structs in containers. I have a multiset of Event structs. I'm trying to find one of these structs by searching on its key. I get the compiler error commented below. struct Event { public: bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } bool operator > ( const Event & rhs ) const { return ( time > rhs.time ); } bool operator == ( const Event & rhs ) const { return ( time == rhs.time ); } double time; int eventID; int hostID; int s; }; typedef std::multiset< Event, std::less< Event > > EventPQ; EventPQ currentEvents; double oldRecTime = 20.0; EventPQ::iterator ceItr = currentEvents.find( EventPQ::key_type( oldRecTime ) ); // no matching function call I've tried a few permutations to no avail. I thought defining the conditional equality operator was going to be enough.

  Read the article

• escape exactly what in javascript

  - by Emin

  Hi all, Being a newbie in javascript I came to a situation where I need more information on escaping characters in a string. Basically I know that in order to escape " I need to replace it with \" but what I don't know is for which characters I need to escape a particular string for. Is there a list of these "characters to escape"? or is it any character that is not a-zA-Z0-9 ? In my situation, I don't have control over the content that is being displayed on my page. Users enter some text and save it. I then use a webservice to extract them from the database, build a json array of objects, then iterate the array when I need to display them. In this case, I have - naturally - no idea of what the text the user has entered and therefore for what characters I need to escape. I also use jQuery for this specific project (just in case it has a function I am not aware of, to do what I need) Providing examples would be appreciated but I also want to learn the theory and logic behind it. Hope someone can be of any help.

  Read the article

• Build system for multi-language project

  - by Epcylon

  I am getting ready to embark on a project mainly for experimenting with languages, but also with a hint of usefulness. It will consist of a server-application, written in Erlang, and client-libraries in a number of languages. Initially I will want to write clients in Java, Ruby and Python. The actual protocol for communication will be Thrift. I'm looking for a build system that will allow me to build the server and all the client libraries in one go, running unit-tests in each language, then packaging up a releasable artifact of some sort in whatever way is the "standard" for each language. That means a Jar for Java, a RubyGem and a distribute/setuptools tarball for Python. Erlang probably has something too, but I'm not yet familiar with that. It should also be able to run the Thrift compiler to generate the various Thrift-stubs in each language. On the pad at the start is Maven. I'm fairly certain Maven can do all I need, but I fear it's too Java-centric, and leaves me with a ton of work for every new language I need to add.

  Read the article

• How good idea is it to use code contracts in Visual Studio 2010 Professional (ie. no static checking

  - by Lasse V. Karlsen

  I create class libraries, some which are used by others around the world, and now that I'm starting to use Visual Studio 2010 I'm wondering how good idea it is for me to switch to using code contracts, instead of regular old-style if-statements. ie. instead of this: if (String.IsNullOrWhiteSpace(fileName)) throw new ArgumentNullException("fileName"); (yes, I know, if it is whitespace, it isn't strictly null) use this: Contract.Requires(!String.IsNullOrWhiteSpace(fileName)); The reason I'm asking is that I know that the static checker is not available to me, so I'm a bit nervous about some assumptions that I make, that the compiler cannot verify. This might lead to the class library not compiling for someone that downloads it, when they have the static checker. This, coupled with the fact that I cannot even reproduce the problem, would make it tiresome to fix, and I would gather that it doesn't speak volumes to the quality of my class library if it seemingly doesn't even compile out of the box. So I have a few questions: Is the static checker on by default if you have access to it? Or is there a setting I need to switch on in the class library (and since I don't have the static checker, I won't) Are my fears unwarranted? Is the above scenario a real problem? Any advice would be welcome.

  Read the article

• Porting Perl to C++ `print "\x{2501}" x 12;`

  - by jippie

  I am porting a program from Perl to C++ as a learning objective. I arrived at a routine that draws a table with commands like the following: Perl: print "\x{2501}" x 12; And it draws 12 times a '?' ("box drawings heavy horizontal"). Now I figured out part of the problem already: Perl: \x{}, \x00 Hexadecimal escape sequence; C++: \unnnn To print a single Unicode character: C++: printf( "\u250f\n" ); But does C++ have a smart equivalent for the 'x' operator or would it come down to a for loop? UPDATE Let me include the full source code I am trying to compile with the proposed solution. The compiler does throw an errors: g++ -Wall -Werror project.cpp -o project project.cpp: In function ‘int main(int, char**)’: project.cpp:38:3: error: ‘string’ is not a member of ‘std’ project.cpp:38:15: error: expected ‘;’ before ‘s’ project.cpp:39:3: error: ‘cout’ is not a member of ‘std’ project.cpp:39:16: error: ‘s’ was not declared in this scope #include <stdlib.h> #include <stdint.h> #include <stdio.h> #include <string.h> int main ( int argc, char *argv[] ) { if ( argc != 2 ) { fprintf( stderr , "usage: %s matrix\n", argv[0] ); exit( 2 ); } else { //std::string s(12, "\u250f" ); std::string s(12, "u" ); std::cout << s; } }

  Read the article

• C++ template type deduction problem

  - by hamishmcn

  motivation: I would like to create a utility class so that instead of having to write: if( someVal == val1 || someVal == val2 || someVal == val3 ) I could instead write: if( is(someVal).in(val1, val2, val3) ) which is much closer to the mathematical 'a is an element of (b,c,d)' and also would save on a lot of typing when the variable name 'someVal' is long. Here is the code I have so far (for 2 and 3 values): template<class T> class is { private: T t_; public: is(T t) : t_(t) { } bool in(const T& v1, const T& v2) { return t_ == v1 || t_ == v2; } bool in(const T& v1, const T& v2, const T& v3) { return t_ == v1 || t_ == v2 || t_ == v3; } }; However it fails to compile if I write: is(1).in(3,4,5); instead I have to write is<int>(1).in(3,4,5); Which isn't too bad, but it would be better if somehow the compiler could figure out that the type is int with out me having to explicitly specify it. Is there anyway to do this or I am stuck with specifying it explicitly?

  Read the article

• page loads twice due to js code

  - by Cristian Boariu

  Hi, I have this div inside a repeater, where i set the class, onmouseover and onmouseout properties from code behind: <div id="Div1" runat="server" class="<%# getClassProduct(Container.ItemIndex) %>" onmouseover="<%# getClassProductOver(Container.ItemIndex) %>" onmouseout="<%# getClassProductOut(Container.ItemIndex) %>"> codebehind: public String getClassProduct(Object index) { int indexItem = Int32.Parse(index.ToString()); if (indexItem == 3) return "produs_box produs_box_wrap overitem lastbox"; else return "produs_box produs_box_wrap overitem"; } public String getClassProductOver(Object index) { int indexItem = Int32.Parse(index.ToString()); if (indexItem == 3) return "this.className='produs_box produs_box_wrap overitem_ lastbox'"; else return "this.className='produs_box produs_box_wrap overitem_'"; } public String getClassProductOut(Object index) { int indexItem = Int32.Parse(index.ToString()); if (indexItem == 3) return "this.className='produs_box produs_box_wrap overitem lastbox'"; else return "this.className='produs_box produs_box_wrap overitem'"; } Well, the problem is that, my Page_Load is fired twice, and there i have some code which i want to execute only ONCE: if (!Page.IsPostBack) { ..code to execute once } This code is fired initially, and after the page is rendered, it is called again, and executed again due to that js... Anyone can recommend a workaround? Thanks in advance.

  Read the article

• Asynchronous Controller is blocking requests in ASP.NET MVC through jQuery

  - by Jason

  I have just started using the AsyncController in my project to take care of some long-running reports. Seemed ideal at the time since I could kick off the report and then perform a few other actions while waiting for it to come back and populate elements on the screen. My controller looks a bit like this. I tried to use a thread to perform the long task which I'd hoped would free up the controller to take more requests: public class ReportsController : AsyncController { public void LongRunningActionAsync() { AsyncManager.OutstandingOperations.Increment(); var newThread = new Thread(LongTask); newThread.Start(); } private void LongTask() { // Do something that takes a really long time //....... AsyncManager.OutstandingOperations.Decrement(); } public ActionResult LongRunningActionCompleted(string message) { // Set some data up on the view or something... return View(); } public JsonResult AnotherControllerAction() { // Do a quick task... return Json("..."); } } But what I am finding is that when I call LongRunningAction using the jQuery ajax request, any further requests I make after that back up behind it and are not processed until LongRunningAction completes. For example, call LongRunningAction which takes 10 seconds and then call AnotherControllerAction which is less than a second. AnotherControllerAction simply waits until LongRunningAction completes before returning a result. I've also checked the jQuery code, but this still happens if I specifically set "async: true": $.ajax({ async: true, type: "POST", url: "/Reports.aspx/LongRunningAction", dataType: "html", success: function(data, textStatus, XMLHttpRequest) { // ... }, error: function(XMLHttpRequest, textStatus, errorThrown) { // ... } }); At the moment I just have to assume that I'm using it incorrectly, but I'm hoping one of you guys can clear my mental block!

  Read the article

• Function returning pointer to struct

  - by GammaGuy

  I am having some issues with code that is returning a pointer to a struct declared inside a class. Here is my code so far: SortedList.h #ifndef SORTEDLIST_H #define SORTEDLIST_H class SortedList{ public: SortedList(); ... private: struct Listnode { Student *student; Listnode *next; }; static Listnode *copyList (Listnode *L); }; #endif SortedList.cpp #include "SortedList.h" ... // Here is where the problem lies Listnode SortedList::*copyList(Listnode *L) { return 0; // for NULL } Apparently, the copy list method wont compile. I am using Microsoft Visual Studio and the compiler tells me that "Listnode" is unidentified. When I try to compile, here is whhat I get: 1>------ Build started: Project: Program3, Configuration: Debug Win32 ------ 1> SortedList.cpp 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C2657: 'SortedList::*' found at the start of a statement (did you forget to specify a type?) 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C2065: 'L' : undeclared identifier 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): fatal error C1903: unable to recover from previous error(s); stopping compilation ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Help would be greatly appreciated...ASAP

  Read the article

• DataTrigger not reevaluating after property changes

  - by frozen

  I have a listbox which has its itemssource (this is done in the code behind on as the window is created) databound to an observable collection. The List box then has the following data template assigned against the items: usercontrol.xaml ... <ListBox x:Name="communicatorListPhoneControls" ItemContainerStyle="{StaticResource templateForCalls}"/> ... app.xaml ... <Style x:Key="templateForCalls" TargetType="{x:Type ListBoxItem}"> <Setter Property="ContentTemplate" Value="{StaticResource templateRinging}"/> <Style.Triggers> <DataTrigger Binding="{Binding Path=hasBeenAnswered}" Value="True"> <Setter Property="ContentTemplate" Value="{StaticResource templateAnswered}"/> </DataTrigger> </Style.Triggers> </Style> ... When the observable collection is updated with an object, this appears in the listbox with the correct initial datatemplate, however when the "hasBeenAnswered" property is set to true (when debugging i can see the collection is correct) the datatrigger does not re-evaluate and then update the listbox to use the correct data template. I have implemented the INotifyPropertyChanged Event in my object, and if in the template i bind to a value, i can see the value update. Its just that the datatrigger will not re-evaluate and change to the correct template. I know the datatrigger binding is correct because if i close the window and open it again, it will correctly apply the second datatemplate, because the "hasBeenAnswered" is set to True.

  Read the article

• Theme-aware XAML resources in a WP7 project

  - by SandRock

  I'm making a Windows Phone 7 application and I'm a bit confused with dark/light themes. With a panorama, you very often set a background image. The issue is it's very hard to make a picture which is right for both dark and light themes. How are we supposed to proceed? Is there a way to force a dark/light theme for a panorama? This will avoid making theme-specific panorama background pictures. Then how do I do? I found xaml files in C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.0\Design. If this is a right way to proceed, how can I import them for my panorama? Or if there's no way (or if it's wrong) to force a dark/light theme: how to write conditional XAML to set correct resources? Now I have the following XAML which is fine with the dark theme: <ImageBrush x:Key="PageBackground" ImageSource="Resources/PageBackground.png" Stretch="None" /> <ImageBrush x:Key="PanoramaBackground" ImageSource="Resources/PanoramaBackground.png" Stretch="None" /> But when I use a light theme, black controls and black texts are hard to read with my dark background pictures. So I made different pictures that I can use this way: <ImageBrush x:Key="PageBackground" ImageSource="Resources/PageBackgroundLight.png" Stretch="None" /> <ImageBrush x:Key="PanoramaBackground" ImageSource="Resources/PanoramaBackgroundLight.png" Stretch="None" /> Now my issue is to make XAML conditionnal to declare the right thing depending on the current theme. I found no relevant way on the Internet. I would prefer not to use code or code-behind for that because I believe XAML is able to do this (I just don't know how).

  Read the article

• DIV inside TD to make it appear correctly

  - by Daniel Svensson

  Hi, I have a <table> generated from code-behind and now facing a problem. In one of the TD i need to have a DIV that is setup with JQuery so that when i click a link the DIV slideToggles. Now i need the TD belonging to that TR not to expand the TR. To solve this i have used an old trick that is to place the JQuery DIV inside another surrounding DIV with height 1px and make the TR not expanding with the heigth of the DIV that slides out. In IE the sliding DIV is partially under the table and in Firefox the DIV appears over the table but it's trasparent, the text from the data in the table shows thru. I have tried to alter the Z-index in various ways but it's no good. Anyone that has an idea or alternatively solution that has worked for them. HtmlGenericControl containerDiv = new HtmlGenericControl("div"); containerDiv.ID = "containerDiv"; containerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.Width, "100%"); containerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.Height, "1px"); containerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.ZIndex, "999"); HtmlGenericControl innerDiv = new HtmlGenericControl("div"); innerDiv.ID = System.Guid.NewGuid().ToString() + "_annualDiv"; inner.Style.Add(System.Web.UI.HtmlTextWriterStyle.Width, "100%"); innerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.Height, "300px"); innerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.ZIndex, "1000"); innerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BorderStyle, "solid"); innerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BorderColor, "Black"); innerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BorderWidth, "1px"); innerDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BackgroundColor, "white"); innerDiv.InnerHtml = "Here is a list of links coming later"; conDiv.Controls.Add(innerDiv);

  Read the article

• I want a function to return a type of the subclass its invoked from

  - by Jay

  I want to have a function defined in a superclass that returns a value of the type of the subclass that is used to invoke the function. That is, say I have class A with a function plugh. Then I create subclasses B and C that extend A. I want B.plugh to return a B and C.plugh to return a C. Yes, they could return an A, but then the caller would have to either cast it to the right subtype, which is a pain when used a lot, or declare the receiving variable to be of the supertype, which loses type safety. So I was trying to do this with generics, writing something like this: class A<T extends A> { private T foo; public T getFoo() { return foo; } } class B extends A<B> { public void calcFoo() { foo=... whatever ... } } class C extends A<C> { public void calcFoo() { foo=... whatever ... } } This appears to work but it looks pretty ugly. For one thing, I get warnings on "class A". The compiler says that A is generic and I should specify the type. I guess it wants me to say "class A". But what would I put in for x? I think I could get stuck in an infinite loop here. It seems weird to write "class B extends A", but this causes no complaints, so maybe that's just fine. Is this the right way to do it? Is there a better way?

  Read the article

• Is it not possible to make a C++ application "Crash Proof"?

  - by Enno Shioji

  Let's say we have an SDK in C++ that accepts some binary data (like a picture) and does something. Is it not possible to make this SDK "crash-proof"? By crash I primarily mean forceful termination by the OS upon memory access violation, due to invalid input passed by the user (like an abnormally short junk data). I have no experience with C++, but when I googled, I found several means that sounded like a solution (use a vector instead of an array, configure the compiler so that automatic bounds check is performed, etc.). When I presented this to the developer, he said it is still not possible.. Not that I don't believe him, but if so, how is language like Java handling this? I thought the JVM performs everytime a bounds check. If so, why can't one do the same thing in C++ manually? UPDATE By "Crash proof" I don't mean that the application does not terminate. I mean it should not abruptly terminate without information of what happened (I mean it will dump core etc., but is it not possible to display a message like "Argument x was not valid" etc.?)

  Read the article

• Why doesn't g++ pay attention to __attribute__((pure)) for virtual functions?

  - by jchl

  According to the GCC documentation, __attribute__((pure)) tells the compiler that a function has no side-effects, and so it can be subject to common subexpression elimination. This attribute appears to work for non-virtual functions, but not for virtual functions. For example, consider the following code: extern void f( int ); class C { public: int a1(); int a2() __attribute__((pure)); virtual int b1(); virtual int b2() __attribute__((pure)); }; void test_a1( C *c ) { if( c->a1() ) { f( c->a1() ); } } void test_a2( C *c ) { if( c->a2() ) { f( c->a2() ); } } void test_b1( C *c ) { if( c->b1() ) { f( c->b1() ); } } void test_b2( C *c ) { if( c->b2() ) { f( c->b2() ); } } When compiled with optimization enabled (either -O2 or -Os), test_a2() only calls C::a2() once, but test_b2() calls b2() twice. Is there a reason for this? Is it because, even though the implementation in class C is pure, g++ can't assume that the implementation in every subclass will also be pure? If so, is there a way to tell g++ that this virtual function and every subclass's implementation will be pure?

  Read the article

• C++: Simple data type for a variable in IF statement?

  - by Jason

  I am new to C++ and am making a simple text RPG, anyway, The scenario is I have a "welcome" screen with choices 1-3, and have a simple IF statement to check them, here: int choice; std::cout << "--> "; std::cin >> choice; if(choice == 1) { //.. That works fine, but if someone enters a letter as selection (instead of 1, 2 or 3) it'll become "-392493492"or something and crash the program. So I came up with: char choice; std::cout << "--> "; std::cin >> choice; if(choice == 1) { //.. This works kinda fine, but when I enter a number it seems to skip the IF statements completely.. Is the char "1" the same as the number 1? I get a compiler errro with this (ISO-CPP or something): if(choice == "1") So how on earth do I see if they entered 1-3 correctly!?

  Read the article

• JavaScript for loop index strangeness

  - by pythonBOI

  I'm relatively new to JS so this may be a common problem, but I noticed something strange when dealing with for loops and the onclick function. I was able to replicate the problem with this code: <html> <head> <script type="text/javascript"> window.onload = function () { var buttons = document.getElementsByTagName('a'); for (var i=0; i<2; i++) { buttons[i].onclick = function () { alert(i); return false; } } } </script> </head> <body> <a href="">hi</a> <br /> <a href="">bye</a> </body> </html> When clicking the links I would expect to get '0' and '1', but instead I get '2' for both of them. Why is this? BTW, I managed to solve my particular problem by using the 'this' keyword, but I'm still curious as to what is behind this behavior.

  Read the article

• Getting values from another winform and passing it to current!

  - by klm9971

  Hello: I have 2 windows forms. The 1st one who gets active during start of the program has a button in which another 2nd windows form appears which has text field in which user type their name and HIT okay. Now in the 1st form I have a variable name: nameproccessed which takes the name from the second form. But the problem is my button which is in the 1st form has more functions besides taking name, how can I stop the flow of the compiler to take first the name from the second form and then process the rest execution of the function??? Here is the snippet of my code: //1st form //Class1 public string _nameProcessed = ""; private void btnGetSomething_Click(object sender, EventArgs e) { showdial(); //some more functionalities in this function!!! } private void showdial() { InputName inm = new InputName(); inm.Show(); } //2nd form //Class2 public string name; private void btnEnterName_Click(object sender, EventArgs e) { name = tbxName.Text; Class1 ict = new Class1(); ict._nameProcessed = name; this.Close(); } Now I want to take the 'name' from the second form put it on the _nameprocessed in the 1st form and then execute the rest of the function. How can I do that? Any help!

  Read the article

• [c++] accessing the hidden 'this' pointer

  - by Kyle

  I have a GUI architecture wherein elements fire events like so: guiManager->fireEvent(BUTTON_CLICKED, this); Every single event fired passes 'this' as the caller of the event. There is never a time I dont want to pass 'this', and further, no pointer except for 'this' should ever be passed. This brings me to a problem: How can I assert that fireEvent is never given a pointer other than 'this', and how can I simplify (and homogenize) calls to fireEvent to just: guiManager->fireEvent(BUTTON_CLICKED); At this point, I'm reminded of a fairly common compiler error when you write something like this: class A { public: void foo() {} }; class B { void oops() { const A* a = new A; a->foo(); } }; int main() { return 0; } Compiling this will give you ../src/sandbox.cpp: In member function ‘void B::oops()’: ../src/sandbox.cpp:7: error: passing ‘const A’ as ‘this’ argument of ‘void A::foo()’ discards qualifiers because member functions pass 'this' as a hidden parameter. "Aha!" I say. This (no pun intended) is exactly what I want. If I could somehow access the hidden 'this' pointer, it would solve both issues I mentioned earlier. The problem is, as far as I know you can't (can you?) and if you could, there would be outcries of "but it would break encapsulation!" Except I'm already passing 'this' every time, so what more could it break. So, is there a way to access the hidden 'this', and if not are there any idioms or alternative approaches that are more elegant than passing 'this' every time?

  Read the article

< Previous Page | 338 339 340 341 342 343 344 345 346 347 348 349  | Next Page >