Virtual function overriding

Hi
I am having a strange problem in my application. I have a virtual method in a base class which I override in the sub class. In my application I instantiate the subclass . This virtual function is then called from a function in the base class . Most of the time this works okay i.e. the overriden function from the subclass gets called but sometimes , for some reason , the base class function gets called , although I verified that the subclass has been instantiated properly.
Any ideas what the problem could be ? . Is there any way to debug this , or view the virtual funtion table.
Any help would be highly appreciated.
Thanks
Santosh

1. Probably you have slicing problem, it happens when you are passing your derived class object where you have defined to pass base class object. In this case your derived class object will be sliced and you will have base class object.
You have two solutions-
1. First thing is you should define the functionality of this function in the base class, bcs it seems this functionality belongs to base class as you are trying to use it there.
2. Dynamically cast the object to your derived class and then call the function. See if it helps.

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Warning :: Derived class hides the base class virtual function

We are porting from CC5.3 to CC5.8 compiler with Sun Studio one compiler. After plenty of hurdles we are in the final stage of removing the warning messages... Amoung the plenty the following one is very common and in different files. Why am I getting this error in 5.8 and not in 5.3 compiler....
Warning: derived_Object::markRead Hides the virtual function base_Object::markRead(ut_SourceCodeLocation&) const in a virtual base
From this it is easily understandable that the base class mark read was hidden by derived class markRead... when we drive and override the derived class function.... It is all over the place....
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//public: using xx_Object :: markRead;
virtual void markRead() const;

The Sun C++ FAQ discusses the warning message:
http://developers.sun.com/prodtech/cc/documentation/ss11/mr/READMEs/c++_faq.html#Coding1
Notice that warnings are not necessarily errors. But I applaud your desire to fix the code so that it generates no warnings. I wish more of our customers could be persuaded to do the same. :-)
C++ 5.3 issues this warning, by the way. Example:
struct B { virtual int foo(int); };
struct D : B { virtual int foo(double); }; // line 2
D d;
line 2: Warning: D::foo hides the virtual function B::foo(int).
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Calling virtual function recursively

Hello,
I have a virtual function foo() in class A which, under certain conditions, will call itself.
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When the code in class A executes, the recursive call this.foo() will call the function in class B (because I am in a class B object), no?
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thanks and regards,
mohan

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For general advice see Troubleshooting issues with iTunes for Windows updates.
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tt2

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For general advice see Troubleshooting issues with iTunes for Windows updates.
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tt2

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Runtime Error!
Program E:\Progra...
R6025
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Point taken...
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Virtual function problem with SC 4.2

Hi
I'm using SC CC 4.2
[CC -V
CC: WorkShop Compilers 4.2 18 Sep 1997 C++ 4.2 patch 104631-04]
not the latest patch, I realize.
The following bit of code:
ProcessParameters *ppp = &(_config.process_params_);
ppp->save_to_file(String("abc"));
config.processparams_.save_to_file(String("xyz"));
does not work as I'd expect it to!
config.processparams_ is of type ProcessParametersEnhanced,
and the definition of this, and its base class, looks like:
class ProcessParameters
public:
virtual int save_to_file(String filename);
and
class ProcessParametersEnhanced : public ProcessParameters
public:
virtual int save_to_file(String filename);
(I've cut everything else out of the class definitions for clarity, and I've changed the names a bit as well, hopefully without typos).
ppp->save_to_file(String("abc"));
calls ProcessParameters::save_to_file(String)
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I've tried building a small test application, using the minimum class interfaces, but this works as I'd expect (it also works fine with gcc).
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TIA
Paul Floyd

Oh well, it was an SC4.2 bug
Patch-ID# 104631-07
Keywords: C++ 4.2 SC4.2
Synopsis: SPARCompiler C++ 4.2: C++ 4.2 patch for Solaris 2.x
Date: Jul/17/98
4066271 C++ has a problem with a copy constructor using virtual and multiple inheritance
It seems as though the copy ctor doesn't copy the vtbl.
Cheers
Paul

A non abstract child class must implement all pure virtual function of parent abstract class in c++

Hi,
In Indesign SDK there is a class IActionComponent having two pure virtual functions:
virtual void
UpdateActionStates(IActiveContext* ac, IActionStateList *listToUpdateGSysPoint mousePoint = kInvalidMousePoint, IPMUnknown* widget = nil) = 0;
virtual void
DoAction(IActiveContext* ac, ActionID actionID, GSysPoint mousePoint = kInvalidMousePoint, IPMUnknown* widget = nil)= 0;
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class WIDGET_DECL CActionComponent : public IActionComponent
implements only UpdateActionStates function and not DoAction function.
There is no compilation error and the code is running fine..HOW
Can some one please explain me?

Oops!!! there is a small correction in my C++ program. The JunkMethod is being called from the constructor...like the following code.
#include <iostream.h>
#include <stdlib.h>
class Base
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            cout<<"In Base Class constructor..."<<endl;
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        virtual void TestAbsFunc()= 0;
class TestAbstract:public Base
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            cout<<"In TestAbsFunc...."<<endl;
int main()
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}You can see the change in the constructor of the Base class. JunkMethod is being called, just to bluff the compiler to call the virtual method (so that it won't crib saying that abstract method cannot be called from the constructor). When Java is supporting this functionality without giving any errors, C++ gives errors when you call an abstract method from the constructor or fails to execute when I do some work around like this. Isn't it a drawback of abstract funcationality supported by C++ (I'm not sure if it's a drawback or not)
Regards,
Kalyan.

Equivelant of "virtual function" from C++ in Java?

I have a Java class which implements a network protocol. There are certain types of packets that my Java class will handle internally. Then again there are other types of packets my Java class needs to pass on to the Java MIDlet that is running this code (importing the package which implements the network protocol and using the class). In C++ I would make this all one class which has a virtual function OnReceive(). Then the C++ application using the class would provide their own implementation for OnReceive and every packet that my network code didn't know what to do with would be passed on to the new OnReceive. How can I do the same in Java? I would like to be able to create a new project, import my package which has the networking code in it. And code up a method that is specific to the application using the networking package. That way I only code one method to handle the packets that my networking code does not care about. I hope someone understands what I am getting at here, it is not so easy to explain.

Make your class abstract, define the pure virtual methods you want subclasseses to provide implementation for (using the abstract keyword in their definition) and you should be good.
public abstract class MyClass {
    public void concreteInitThing() {
        // your code here
    public abstract void specificImplementation();
public class ConcreteImplementationOfMyClass extends MyClass {
    public void specificImplementation() {
        // Your code here
}I hope that helped
Lee

Dbx - pure virtual function - (not)

I have a very large application developed under SunStudio12 on Solaris 10. I just built it on Fedora 7 using the linux version of SunStudio12. It builds and runs just fine.
However, when I try to debug the application I get weird behavior. For example, I can set a breakpoint in a routine which I know gets called, but execution does not stop there.
Even worse, I can try to set a breakpoint in a routine, and it will not let me because it thinks it is "pure virtual":
(dbx) stop in WspanXML::GetFare
dbx: `GetFare' is a pure virtual function
WspanXML::GetFare is not pure virtual. It is defined like this:
class WspanXML : public CRSapi {
bool GetFare(fare_breakdown & fare, string & fare_desc,
PNR & work_pnr, bool lowest);
GetFare is pure virtual in the base class:
class CRSapi {
virtual bool GetFare(fare_breakdown & fare, string & fare_desc,
PNR & work_pnr, bool lowest) = 0;
Is this a known problem with the linux version of SunStudio12 or do I have something miss-configured?
Thank you,
John

No, this is not a known problem. And I couldn't reproduce
it with a small test case. Would you please do the following
to help us verify if the debugging info generated is correct:
% dwarfdump <your_application> | more
/WspanXML - to search for class WspanXML
/GetFare - then method GetFare
/DW_AT_virtuality
Does the DW_AT_virtuality field say DW_VIRTUALITY_virtual
or DW_VIRTUALITY_pure_virtual?
Thanks.

[solved] Template virtual function in C++

I know this isn't legal C++ due to the compiler not being able to determine how big exactly the vtable is. I'm looking for alternatives.
Basically, I have an abstract base class defining the interface for a set of derived classes. One of the functions being exposed through this interface is called run(). Each derived class does something different with run(). So it looks something like this:-
class base {
protected:
base() { }
public:
virtual void run(...) = 0;
/* rest of api here */
class derived : public base {
private:
template<class T>
void runTemplate() {
/* Do something with data-type T */
public:
void run(...) {
switch(some_int_value_from_the_input) {
case 1:
runTemplate<char>();
break;
case 2:
runTemplate<short>();
break;
case 3:
runTemplate<int>();
break;
default:
/* throw error */
My 'problem' is that every single derived class has exactly the same run() function, they only differ in the algorithm within runTemplate(). However, since I'm not allowed to implement run() in base calling a templated virtual function in base, I seem forced to have the code above, which seems to me to unnecessarily duplicate code.
Is there another way to implement the above? My objective is to keep the amount of coding done in the derived class to the bare minimum (pretty much just the algorithm if possible), hence why I'm trying to move run()'s definition from derived to base.
Last edited by ngoonee (2009-10-07 14:11:01)

scio wrote:
Sorry I typing to you and talking to someone else... I meant polymorphism.
However, I'm not sure if I understand your end goal. It seems like templates are not needed, but there might be a reason in your code:
class base {
protected:
base() { }
public:
virtual void run(...) = 0;
/* rest of api here */
class algowrapper{
public:
algowrapper(...) {
/* Use arg to setup algorithm /*
static void processInput(...) {
/* Do something with input and defined algorithm */
class runner : public base{
protected:
runner():algo(NULL) { }
algowrapper* algo;
public:
virtual void run(...) {
if (algo)
algo->processInput();
class derived : public runner{
public:
derived(...):runner(),algo(new algowrapper(/* some algorithm */)) { }
class derived2 : public runner{
public:
derived(...):runner(),algo(new algowrapper(/* different algorithm */)) { }
Hmmm, looks like my explaining skills leave a lot to be desired. Basically I want the separate algorithms to be fully implemented within the derived classes.
Usage case is that, for example, I distribute my executable which includes the object file for base. One of the things my executable does is load .so files (using dlopen), which will be compiled separately from the main executable. These .so files return a pointer to base, but different .so files implement different algorithms. So I can only access the functions which belong to base, since all I have is a pointer to base and no knowledge of the specific derived class, and i just call base->run(...) which is implemented in each derived class and it should handle the rest.
The problem, as I see it, is that runtemplate() shouldn't need to be part of the API in base, yet if it doesn't exist in base, run() cannot call it. Even if it exists in base, it cannot have the form of a template since this is illegal in C++.

Application Class Loader problem calling virtual function

Hello everyone
I have run in to very strange behavior of JVM
I have created a class loader which allows my to load classes from
jar file, regardless that URLClassLoader supplies this functionality.
I am using this class loader to load some classes and call their virtual functions. The class diagram looks like that:
public interface I {
   public void init();
public class AAA implements
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public class BBB extends AAA{
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}Interface I and class AAA are loaded with System Class loader and Class BBB is loaded using my class loader from jar file.
ByteStreamClassLoader classLoader = new ByteStreamClassLoader ();
Class cl = classLoader. loadClass(�com.product.BBB�,true);
I myInterface = cl.newInstance();
myInterface.init();The problem is that from some unknown reason java class AAA.init() instead of BBB.init().
Can somebody help me what am I doing wrong?
Class Loader code attached below
public class ByteStreamClassLoader   extends ClassLoader {
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      String[] packageArray = className.split("\\.");
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String packageName = strB.toString();
packageName = packageName.substring(0, packageName.length() - 1);
if (getPackage(packageName) == null) {
m_logger.log(Level.FINEST, "Defining package '" + packageName + "'");
definePackage(packageName, null, null, null, null, null, null, null);
return packageName;
public synchronized Class loadClass(String name, boolean resolve) throws
ClassNotFoundException {
name = name.replaceAll("/", ".").replaceAll(".class", "");
//Try to locate the Class in cashe
Class c = (Class) m_cache.get(name);
//Try to locate the Class in the System Class Loader
if (c == null) {
try {
c = ClassLoader.getSystemClassLoader().loadClass(name);
catch (Exception ex) {}
else {
m_logger.log(Level.FINEST, "Class '" + name + "' found in cache");
//Load the class from byte array
if (c == null) {
String resourceName = name;
if (!resourceName.endsWith(".class")) {
resourceName = resourceName.concat(".class");
//Retrieve class byte representation
if (resourceName.indexOf(".") != -1) {
resourceName =
resourceName.replaceAll("\\.", "/").replaceAll("/class", ".class");
//Use the ByteStreamClassLoader to load the class from byte array
byte[] classByteArray = null;
try {
classByteArray = getResourceBytes(resourceName);
catch (IOException ex1) {
throw new ClassNotFoundException(
"Could not load class data." + ex1.getMessage());
m_logger.log(
Level.FINEST, "Loading class '" +
name + "' Byte Length: " + classByteArray.length);
String p = definePackage(name);
c = defineClass(
name,
classByteArray,
0,
classByteArray.length,
ByteStreamClassLoader.class.getProtectionDomain());
m_cache.put(name, c);
if (resolve) {
resolveClass(c);
return c;

Hello everyone
I have run in to very strange behavior of JVM
I have created a class loader which allows my to load classes from
jar file, regardless that URLClassLoader supplies this functionality.
I am using this class loader to load some classes and call their virtual functions. The class diagram looks like that:
public interface I {
   public void init();
public class AAA implements
   public void init(){
public class BBB extends AAA{
   public void init(){
      //here comes implementation
}Interface I and class AAA are loaded with System Class loader and Class BBB is loaded using my class loader from jar file.
ByteStreamClassLoader classLoader = new ByteStreamClassLoader ();
Class cl = classLoader. loadClass(�com.product.BBB�,true);
I myInterface = cl.newInstance();
myInterface.init();The problem is that from some unknown reason java class AAA.init() instead of BBB.init().
Can somebody help me what am I doing wrong?
Class Loader code attached below
public class ByteStreamClassLoader   extends ClassLoader {
    protected HashMap m_cache = new HashMap();
    public void clearCashe() {
      m_cache = new HashMap();
    private String definePackage(String className) {
      StringBuilder strB = new StringBuilder();
      //Class name must be removed from the URI in order to define a package
      String[] packageArray = className.split("\\.");
      for (int i = 0; i < packageArray.length - 1; i++) {
        strB.append(packageArray).append(".");
String packageName = strB.toString();
packageName = packageName.substring(0, packageName.length() - 1);
if (getPackage(packageName) == null) {
m_logger.log(Level.FINEST, "Defining package '" + packageName + "'");
definePackage(packageName, null, null, null, null, null, null, null);
return packageName;
public synchronized Class loadClass(String name, boolean resolve) throws
ClassNotFoundException {
name = name.replaceAll("/", ".").replaceAll(".class", "");
//Try to locate the Class in cashe
Class c = (Class) m_cache.get(name);
//Try to locate the Class in the System Class Loader
if (c == null) {
try {
c = ClassLoader.getSystemClassLoader().loadClass(name);
catch (Exception ex) {}
else {
m_logger.log(Level.FINEST, "Class '" + name + "' found in cache");
//Load the class from byte array
if (c == null) {
String resourceName = name;
if (!resourceName.endsWith(".class")) {
resourceName = resourceName.concat(".class");
//Retrieve class byte representation
if (resourceName.indexOf(".") != -1) {
resourceName =
resourceName.replaceAll("\\.", "/").replaceAll("/class", ".class");
//Use the ByteStreamClassLoader to load the class from byte array
byte[] classByteArray = null;
try {
classByteArray = getResourceBytes(resourceName);
catch (IOException ex1) {
throw new ClassNotFoundException(
"Could not load class data." + ex1.getMessage());
m_logger.log(
Level.FINEST, "Loading class '" +
name + "' Byte Length: " + classByteArray.length);
String p = definePackage(name);
c = defineClass(
name,
classByteArray,
0,
classByteArray.length,
ByteStreamClassLoader.class.getProtectionDomain());
m_cache.put(name, c);
if (resolve) {
resolveClass(c);
return c;

I can't search a song or an artist. i get an error R6025/pure virtual function call. then itunes stops working. PLEASE HELP

I can't search a song or an artist without getting an error R6025 - pure virtual function call. Then itunes stops working. How do I fix it? PLEASE HELP

I have had numerous issues with Itunes 64 bit 11.1.38 (and other previous versions) locking up and crashing upon start with "Itunes has stopped working" or "R6027 pure virtual function call". I have researched the answers around the forums as well as having tried some extensive and repetitious troubleshooting myself and thought I'd list them here... in order of troubleshooting...
1. Install all Windows updates and reboot. This seems to clear issues from time-to-time... I suspect Itunes expects the latest-and-greatest as far as Windows is concerned.. see if this clears your issue.
2. Uninstall all Itunes and Apple products & reboot, remove their directories, remove lingering Itunes registry entries, reboot again, reinstall using "RUN AS ADMINISTRATOR" to install the Itunes executable. See if this allows Itunes to stabilize. Pelase be sure to use the following guide from Apple as far as removing the apps and directories are concerned...
http://support.apple.com/kb/ht1923
3. Remove the contents of the "iphone photo cache" (or other related product photo cache) directory.
4. Try editing the shortcut properties and configure the shortcut (for all users) to run as Administrator.
5. Try editing the shortcut and configure it to run in Compatibility Mode for Windows 7 (for all users).
6. a.Try using MSCONFIG to locate a potential conflicting application or service using the following...
http://support.apple.com/kb/ht2292
or
6. b. Remove the last recent software application(s) you may have installed... in my case removing GREENSHOT http://getgreenshot.org/ stopped my Itunes from crashing on startup and it stabilized after
driving my nuts for weeks.
Message was edited by: DaCheeze

Virtual function overriding

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