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• Dynamic Object Not Creating for Privately Inherited Class.

  - by mahesh

  Hi, What is the reason for the following code that does not let me to create object. class base { public: void foo() { cout << "base::foo()"; } }; class derived : private base { public: void foo() { cout << "deived::foo()"; } }; void main() { base *d = new derived(); d->foo(); } It Gives me error : " 'type cast' : conversion from 'derived *' to 'base *' exists, but is inaccessible" Thanks in advance :)

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• Why would you precede the main() function in C with a data type?

  - by Milktrader

  Many are familiar with the hello world program in C #include <stdio.h> main () { printf ("hello world"); return 0; } Why do some precede the main () function with int as in: int main() Also, I've seen the word 'void' entered inside the () as in: int main(void) It seems like extra typing for nothing, but maybe it's a best practice that pays dividends in other situations? Also, why precede main() with an int if you're returning a character string? If anything, one would expect: char main(void) I'm also foggy about why we return 0 at the end of the function.

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• How can I implement a matchmaker?

  - by csiz

  I'm making a multiplayer game, where players are separated in to rooms that would ideally have about 20 players. So I need a few pointers on an algorithm to distribute the players in to these rooms. A few more constraints: When a players gets in to a room, he should stay there until he decides to exit (the room itself changes levels) There may be more room servers, every server should create more rooms until near full capacity There's a central server that manages all the room servers, and directs the players towards their room

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• How does ambigous methods are resolved in java ?

  - by Jijoy

  Hi , I do have a question. package org.study.algos; public class Study { public static void main(String[] args) { A a = new A(); a.m1(null); } } class A { public void m1(String s) { System.out.println("String"); System.out.println(s); } public void m1(Object obj) { System.out.println("Object"); System.out.println(obj); } } Here , the output is String null Why JVM resolve the method to one with String arguement ? Thanks in advance J

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• Java Inheritance Concept Understanding

  - by Nirmal

  Hello All.... I am just refreshing the oops features of the java. So, I have a little confusion regarding inheritance concept. For that I have a following sample code : class Super{ int index = 5; public void printVal(){ System.out.println("Super"); } } class Sub extends Super{ int index = 2; public void printVal(){ System.out.println("Sub"); } } public class Runner { public static void main(String args[]){ Super sup = new Sub(); System.out.println(sup.index+","); sup.printVal(); } } Now above code is giving me output as : 5,Sub. Here, we are overriding printVal() method, so that is understandable that it is accessing child class method only. But I could not understand why it's accessing the value of x from Super class... Thanks in advance....

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• About using assembly with c

  - by kristus

  Hi. I've sort of just finished a mandatory task at school, and I'm about to deliver it. But then I came across something that was unfamiliar, header files. :( What I've got: test-program.c task_header.h function1.s function2.s function3.s function4.s test-program.c: #include <stdio.h> #include <stdlib.h> #include <string.h> #include "task_header.h" . .. ... task_header.h: extern void function1(...); extern void function2(...); extern int function3(...); extern void function4(...); And then I use the command: gcc -m32 -o runtest test-program.c function1.s function2.s function3.s function4.s Is this a proper way to do it, or is it possible to modify it? So I can type: gcc -m32 -o runtest test-program.c ?

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• How to Execute Base Class's Method Before Implementors's Method?

  - by DaveDev

  I have the following page public partial class GenericOfflineCommentary : OfflineFactsheetBase { } where OfflineFactsheetBase is defined as public class OfflineFactsheetBase : System.Web.UI.Page { public OfflineFactsheetBase() { this.Load += new EventHandler(this.Page_Load); this.PreInit += new EventHandler(this.Page_PreInit); } protected void Page_PreInit(object sender, EventArgs e) { if (Request.QueryString["data"] != null) { this.PageData = StringCompressor.DecompressString(Request.QueryString["data"]); this.ExtractPageData(); } } } OfflineFactsheetBase has the following virtual method: public virtual void ExtractPageData() { // get stuff relevant to all pages that impmement OfflineFactsheetBase } which is implemented in all pages that impmement OfflineFactsheetBase as follows: public partial class GenericOfflineCommentary : OfflineFactsheetBase { public override void ExtractPageData() { // get stuff relevant to an OfflineCommentary page. } } Currently, only GenericOfflineCommentary's ExtractPageData() is firing. How can I modify this to first run OfflineFactsheetBase's ExtractPageData() and then GenericOfflineCommentary's? edit: I'm trying to avoid having to call base.ExtractPageData() in every implementor. Is this possible?

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• Is there any way to determine what type of memory the segments returned by VirtualQuery() are?

  - by bdbaddog

  Greetings, I'm able to walk a processes memory map using logic like this: MEMORY_BASIC_INFORMATION mbi; void *lpAddress=(void*)0; while (VirtualQuery(lpAddress,&mbi,sizeof(mbi))) { fprintf(fptr,"Mem base:%-10x start:%-10x Size:%-10x Type:%-10x State:%-10x\n", mbi.AllocationBase, mbi.BaseAddress, mbi.RegionSize, mbi.Type,mbi.State); lpAddress=(void *)((unsigned int)mbi.BaseAddress + (unsigned int)mbi.RegionSize); } I'd like to know if a given segment is used for static allocation, stack, and/or heap and/or other? Is there any way to determine that?

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• Why doesn't C++ allow you to request a pointer to the most derived class?

  - by Matthew Lowe

  (This question should probably be answered with a reference to Stroustrup.) It seems extremely useful to be able to request a pointer to the most derived class, as in the following: class Base { ... }; class DerivedA { ... }; class DerivedB { ... }; class Processor { public: void Do(Base* b) {...} void Do(DerivedA* d) {...} void Do(DerivedB* d) {...} }; list<Base*> things; Processor p; for(list<Base*>::iterator i=things.begin(), e=things.end(); i!=e; ++i) { p.Do(CAST_TO_MOST_DERIVED_CLASS(*i)); } But this mechanism isn't provided in c++. Why?

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• doubt in Exceptions

  - by Ajay Singh

  class MyException extends Exception { MyException() {} MyException(String msg) { super(msg);} } public class NewException { static void f() throws MyException { System.out.println("throwing exception from f()"); throw new ClassCastException(); } static void g() throws MyException { System.out.println("throwing exception from g()"); throw new MyException("parametrized "); } public static void main(String ...strings ) { try { f(); } catch(MyException e) { e.printStackTrace(System.out); } try { g(); } catch(MyException e) { e.printStackTrace(System.out); } } } In the function f() iam specifying that "MyException " exception will be thrown and actually iam throwing some other exception which has no relation with MyException but still the compiler does not report any complain.Why is it so??

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• Java SWING- Create a function to add elements to JScrollPanel ??? PLEASE

  - by battousai622

  I want to create a function so that i can call add JLables, ect inside the JScrollPanel. Im not sure what the command is in netbeans. I tried doing JScrollPanel - events - container - componentAdded to create the code below. But nothing shows up when i add code to that function. Any help would be great please! =] private void initComponents() { scrollPanel = new javax.swing.JScrollPane(); scrollPanel.addContainerListener(new java.awt.event.ContainerAdapter() { public void componentAdded(java.awt.event.ContainerEvent evt) { scrollPanelComponentAdded(evt); } } private void scrollPanelComponentAdded(java.awt.event.ContainerEvent evt) { System.out.println("main"); }

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• Skype 4.0 keeps crashing

  - by Paté

  I just installed Skype 4.0 for Linux and for some reason it crashed almost everytime I click on certain actions like Mark all as viewed, Accept an invitation etc... Apparently It seems to work well for other and I couldn't find any help on that type of behaviour online. I do get the same behaviour on my box at work which makes me believe it comes from something I use but what ? thanks for any pointers.

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• Why this function overloading is not working?

  - by Jack

  class CConfFile { public: CConfFile(const std::string &FileName); ~CConfFile(); ... std::string GetString(const std::string &Section, const std::string &Key); void GetString(const std::string &Section, const std::string &Key, char *Buffer, unsigned int BufferSize); ... } string CConfFile::GetString(const string &Section, const string &Key) { return GetKeyValue(Section, Key); } void GetString(const string &Section, const string &Key, char *Buffer, unsigned int BufferSize) { string Str = GetString(Section, Key); // *** ERROR *** strncpy(Buffer, Str.c_str(), Str.size()); } Why do I get an error too few arguments to function ‘void GetString(const std::string&, const std::string&, char*, unsigned int)' at the second function ? Thanks

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• Java Thread Message Passing

  - by pkulak

  I'm writing an Android app. I have a main method, which creates and runs a new Thread using an anonymous inner Runnable class. The run() method, when it's done, calls a method on it's parent class (in the main thread) that calls notifyDataSetChanged() so that the main thread can redraw the new data. This is causing all kinds of trouble (ViewRoot$CalledFromWrongThreadException). The thing is, this method being called from the worker thread is on the class that's created in the UI thread. Shouldn't that be running on the UI thread? Or am I missing something? Here's some code about what I'm talking about: public class Mealfire extends Activity { @Override public void onCreate(Bundle icicle) { (new Thread() { public void run() { // Do a bunch of slow network stuff. update(); } }).start(); } private void update() { myAdapter.notifyDatasetChanged(); } }

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• C - Call a function

  - by Pedro

  Hello. I want to get a value from a function in other function i think i have to call a function in other function, then call it on main, but how? void funcA(PEOPLE people[], int *total){ FILE *fp; char line[100]; fp=fopen("example.txt","r"); if(fp==NULL){ exit(1); } else{ fgets(line, 100, fp);//get a number from the txt total=atoi(linha);//convert to int } } void funcB(PEOPLE people[], int *total){ int i; for(i=0;i<total;i++){ printf("%s\n",people[i].name); } funcA(people,&total); } void main(){ PERSON person[100]; int *total; funcB(people,&total); } What i'm doing wrong?

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• Global variable in a recursive function how to keep it at zero?

  - by Grammin

  So if I have a recursive function with a global variable var_: int var_; void foo() { if(var_ == 3) return; else var_++; foo(); } and then I have a function that calls foo() so: void bar() { foo(); return; } what is the best way to set var_ =0 everytime foo is called thats not from within itself. I know I could just do: void bar() { var_ =0; foo(); return; } but I'm using the recursive function a lot and I don't want to call foo and forget to set var_=0 at a later date. Does anyone have any suggestions on how to solve this? Thanks, Josh

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• Why does the compiler give an ambiguous invocation error when passing inherited types?

  - by Matt Mitchell

  What is happening in the C# compiler to cause the following ambiguous invocation compilation error? The same issue applies to extension methods, or when TestClass is generic and using instance rather than static methods. class Type1 { } class Type2 : Type1 {} class TestClass { public static void Do<T>(T something, object o) where T : Type1 {} public static void Do(Type1 something, string o) {} } void Main() { var firstInstance = new Type1(); TestClass.Do(firstInstance, new object()); // Calls Do(Type1, obj) TestClass.Do(firstInstance, "Test"); // Calls Do<T>(T, string) var secondInstance = new Type2(); TestClass.Do(secondInstance, new object()); // Calls Do(Type1, obj) TestClass.Do(secondInstance, "Test"); // "The call is ambiguous" compile error }

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• C++ performance, optimizing compiler, empty function in .cpp

  - by Dodo

  I've a very basic class, name it Basic, used in nearly all other files in a bigger project. In some cases, there needs to be debug output, but in release mode, this should not be enabled and be a NOOP. Currently there is a define in the header, which switches a makro on or off, depending on the setting. So this is definetely a NOOP, when switched off. I'm wondering, if I have the following code, if a compiler (MSVS / gcc) is able to optimize out the function call, so that it is again a NOOP. (By doing that, the switch could be in the .cpp and switching will be much faster, compile/link time wise). --Header-- void printDebug(const Basic* p); class Basic { Basic() { simpleSetupCode; // this should be a NOOP in release, // but constructor could be inlined printDebug(this); } }; --Source-- // PRINT_DEBUG defined somewhere else or here #if PRINT_DEBUG void printDebug(const Basic* p) { // Lengthy debug print } #else void printDebug(const Basic* p) {} #endif

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• Debug.writeline locks

  - by Carra

  My program frequently stops with a deadlock. When I do a break-all and look at the threads I see that three threads are stuck in our logging function: public class Logging { public static void WriteClientLog(LogLevel logLevel, string message) { #if DEBUG System.Diagnostics.Debug.WriteLine(String.Format("{0} {1}", DateTime.Now.ToString("HH:mm:ss"), message)); //LOCK #endif //...Log4net logging } } If I let the program continue the threads are still stuck on that line. I can't see where this can lock. The debug class, string class & datetime class seem to be thread safe. The error goes away when I remove the "#if DEBUG System... #endif" code but I'm curious why this behavior happens. Thread one: public void CleanCache() { Logging.WriteClientLog(LogLevel.Debug, "Start clean cache.");//Stuck } Thread two: private void AliveThread() { Logging.WriteClientLog(LogLevel.Debug, "Check connection");//Stuck }

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• ASP.NET null reference exception

  - by nanek

  Please help me to figure out what is wrong with this code: I have ASP.NET page with one button visible. When user clicks it - it instances MyClass (its implementation is in AppCode directory) and turns invisible (button2 becomes visible). When I click button2 it raises "Object reference not set to an instance of an object" Exception. What seems to be the problem? { public MyClass noviTest; protected void Page_Load(object sender, EventArgs e) { } protected void Button1_Click(object sender, EventArgs e) { noviTest = new MyClass(TextBox1.Text); Button1.Visible = false; Button2.Visible = true; } protected void Button2_Click(object sender, EventArgs e) { Label1.Text=noviTest.getID; //this is the critical line } } Thank You in advance, Regards

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• XAML-based applications - Event Naming Conventions for C#

  - by user118190

  For event handling, I am starting to see many coders doing this: XButton.Click += OnXButtonClicked() ... void OnXButtonClicked() { ... } Where did this On_ convention come from? It just doesn't feel right in terms of methods. I am starting to see this as well and am wondering what others thought: XButton.Click += HandleXButtonClick() ... void HandleXButtonClick() { ... } When using intellisense, Visual Studio handles these like so: XButton.Click += XButton_Click; ... void XButton_Click(object sender, RoutedEventArgs e) { ... } I am seeking some advice on these naming conventions and would greatly appreciate some advice.

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• Error while calling a virtual function that is defined in Derived class but not present in Base clas

  - by sandeep

  #include<iostream.h> class A{ public: virtual void fun() {cout<<"A::fun()"; } }; class B : public A { public: virtual void fun() {cout<<"B::fun()"; } virtual void func() {cout<<"B::func"; } }; int main() { A *obj1=new B; obj1->fun(); obj1->func(); }

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• C++ Basic Class Layout

  - by Spencer

  Learning C++ and see the class laid out like this: class CRectangle { int x, y; public: void set_values (int,int); int area () {return (x*y);} }; void CRectangle::set_values (int a, int b) { x = a; y = b; } I know Java and methods(functions) in Java are written within the class. The class looks like a Java interface. I know I can write the class like this: class CRectangle { int x, y; public: void set_values (int a, int b) { x = a; y = b; }; int area () {return (x*y);} }; But is there a difference or standard?

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• Event handling C# / Registering a callback

  - by Jeff Dahmer

  Events can only return void and recieve object sender/eventargs right? If so then craptastic.... how can I pass a function pointer to another obj, like: public bool ACallBackFunc(int n) { return n > 0; } public void RegisterCallback(Something s) { s.GiveCallBack(this.ACallBackFunc); } Something::GiveCallBack(Action? funcPtr) I tried using Action, but I need it to return some value and Actions can only return void. Also, we do not know what kind of a callback we will be recieving; it could return anything and have any params! Reflection will have to be used somehow I reckon.

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• Overriding vs Virtual

  - by anonymous

  What is the purpose of using the reserved word virtual in front of functions? If I want a child class to override a parent function, I just declare the same function such as "void draw(){}". class Parent{ public: void say(){ std::cout << "1"; }}; class Child : public Parent{public:void say(){ std::cout << "2"; } }; int main() { Child* a = new Child(); a->say(); return 0; } The output is 2. So again, why would the reserved word "virtual" be necessary in the header of say() ? Thanks a bunch.

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