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• C++ Switch won't compile with externally defined variable used as case

  - by C Nielsen

  I'm writing C++ using the MinGW GNU compiler and the problem occurs when I try to use an externally defined integer variable as a case in a switch statement. I get the following compiler error: "case label does not reduce to an integer constant". Because I've defined the integer variable as extern I believe that it should compile, does anyone know what the problem may be? Below is an example: test.cpp #include <iostream> #include "x_def.h" int main() { std::cout << "Main Entered" << std::endl; switch(0) { case test_int: std::cout << "Case X" << std::endl; break; default: std::cout << "Case Default" << std::endl; break; } return 0; } x_def.h extern const int test_int; x_def.cpp const int test_int = 0; This code will compile correctly on Visual C++ 2008. Furthermore a Montanan friend of mine checked the ISO C++ standard and it appears that any const-integer expression should work. Is this possibly a compiler bug or have I missed something obvious? Here's my compiler version information: Reading specs from C:/MinGW/bin/../lib/gcc/mingw32/3.4.5/specs Configured with: ../gcc-3.4.5-20060117-3/configure --with-gcc --with-gnu-ld --with-gnu-as --host=mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable-languages=c,c++,f77,ada,objc,java --disable-win32-registry --disable-shared --enable-sjlj-exceptions --enable-libgcj --disable-java-awt --without-x --enable-java-gc=boehm --disable-libgcj-debug --enable-interpreter --enable-hash-synchronization --enable-libstdcxx-debug Thread model: win32 gcc version 3.4.5 (mingw-vista special r3)

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• Launch a QWidget from a QMain window

  - by Opera

  Hello everyone ! I'm doing my first C++ - Qt4 application and I'm having some trouble "connecting" my different uis. I have a main window with several buttons and when I click on one, I want another window to open. The MyMainWindowClass inherits from QMainWindow and the other from QWidget. Here is the code I have written so far : #include <iostream #include "MyWidgetClass.hpp" #include "MyMainWindowClass.hpp" #include "ui_MyMainWindowClassUi.h" MyMainWindowClass::MyMainWindowClass(QWidget *parent) : QMainWindow(parent), m_ui(new Ui::MyMainWindowClassUi) { m_ui-setupUi(this); initConnect(); } void MyMainWindowClass::initConnect() { QObject::connect(m_ui-SomeBtn, SIGNAL(clicked()), this, SLOT(SomeBtnClicked())); // Some other QObject::connect calls return; } void MyMainWindowClass::SomeBtnClicked() { std::cout << "Some Btn has been clicked" << std::endl; this-setEnabled(false); MyWidgetClass mwc(this); mwc.show(); return; } This calls the Ctor and the Dtor from MyWidgetClass, disables the MyMainWindowClassUi, but doesn't show my other GUI. What am I missing to have the window showed when I click on the button ?

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• C++ explicit template specialization of templated constructor of templated class

  - by Victor Liu

  I have a class like template <class T> struct A{ template <class U> A(U u); }; I would like to write an explicit specialization of this for a declaration like A<int>::A(float); In the following test code, if I comment out the specialization, it compiles with g++. Otherwise, it says I have the wrong number of template parameters: #include <iostream> template <class T> struct A{ template <class U> A(T t, U *u){ *u += U(t); } }; template <> template <> A<int>::A<int,float>(int t, float *u){ *u += U(2*t); } int main(){ float f = 0; int i = 1; A<int>(i, &f); std::cout << f << std::endl; return 0; }

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• How to produce 64 bit masks?

  - by egiakoum1984

  Based on the following simple program the bitwise left shit operator works only for 32 bits. Is it true? #include <iostream> #include <stdlib.h> using namespace std; int main(void) { long long currentTrafficTypeValueDec; int input; cout << "Enter input:" << endl; cin >> input; currentTrafficTypeValueDec = 1 << (input - 1); cout << currentTrafficTypeValueDec << endl; cout << (1 << (input - 1)) << endl; return 0; } The output of the program: Enter input: 30 536870912 536870912 Enter input: 62 536870912 536870912 How could I produce 64-bit masks?

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• Problem with futures in c++0x .

  - by Eternal Learner

  Hi, I have written a small program , to understand how futures work in c++0x. while running the code I get an error like " error: 'printEn' was not declared in this scope". I am unable to understand what the problem is..Kindly point out what I am doing wrong here and if possible write the correct code for the same.. #include <future> #include <iostream> using namespace std; int printFn() { for(int i = 0; i < 100; i++) { cout << "thread " << i << endl; } return 1; } int main() { future<int> the_answer2=async(printEn); future<int> the_answer1=async(printEn); return 0; }

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• Getting base address of a process

  - by yoni0505

  I'm trying to make a program that read the timer value from Minesweeper. (OS is windows 7 64bit) Using cheat engine I found the base address of the variable, but it changes every time I run Minesweeper. What do I need to do to find out the base address automatically? Does it have something to do with the executable base address? Here's my code: #include <windows.h> #include <iostream> using namespace std; int main() { DWORD baseAddress = 0xFF1DAA38;//always changing DWORD offset1 = 0x18; DWORD offset2 = 0x20; DWORD pAddress1; DWORD pAddress2; float value = 0; DWORD pid; HWND hwnd; hwnd = FindWindow(NULL,"Minesweeper"); if(!hwnd)//didn't find the window { cout <<"Window not found!\n"; cin.get(); } else { GetWindowThreadProcessId(hwnd,&pid); HANDLE phandle = OpenProcess(PROCESS_VM_READ,0,pid);//get permission to read if(!phandle)//failed to get permission { cout <<"Could not get handle!\n"; cin.get(); } else { ReadProcessMemory(phandle,(void*)(baseAddress),&pAddress1,sizeof(pAddress1),0); ReadProcessMemory(phandle,(void*)(pAddress1 + offset1),&pAddress2,sizeof(pAddress2),0); while(1) { ReadProcessMemory(phandle,(void*)(pAddress2 + offset2),&value,sizeof(value),0); cout << value << "\n"; Sleep(1000); } } } }

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• Problem in printing array of char pointer passing from Python

  - by Yan Cheng CHEOK

  My following C code works quite well, till my Python code trying to pass an array of char pointer to it. The output I obtain is The file_name is python-file Another 3 string is not being printed out. Anything I had missed out? C Code #include <iostream> #include "c_interface.h" int foo(const char* file_name, const char** names) { std::cout << "The file_name is " << file_name << std::endl; while (*names) { std::cout << "The name is " << *names << std::endl; names++; } return 0; } /* int main() { const char *c[] = {"123gh", "456443432", "789", 0}; foo("hello", c); getchar(); } */ Python Code #!c:/Python27/python.exe -u from ctypes import * name0 = "NAME0" name1 = "NAME1" name2 = "NAME2" names = ((c_char_p * 1024) * 4)() names[0].value = name0 names[1].value = name1 names[2].value = name2 names[3].value = 0 libc = CDLL("foo.dll") libc.foo("python-file", names)

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• Why can I call a non-const member function pointer from a const method?

  - by sdg

  A co-worker asked about some code like this that originally had templates in it. I have removed the templates, but the core question remains: why does this compile OK? #include <iostream> class X { public: void foo() { std::cout << "Here\n"; } }; typedef void (X::*XFUNC)() ; class CX { public: explicit CX(X& t, XFUNC xF) : object(t), F(xF) {} void execute() const { (object.*F)(); } private: X& object; XFUNC F; }; int main(int argc, char* argv[]) { X x; const CX cx(x,&X::foo); cx.execute(); return 0; } Given that CX is a const object, and its member function execute is const, therefore inside CX::execute the this pointer is const. But I am able to call a non-const member function through a member function pointer. Are member function pointers a documented hole in the const-ness of the world? What (presumably obvious to others) issue have we missed?

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• Class Assignment Operators

  - by Maxpm

  I made the following operator overloading test: #include <iostream> #include <string> using namespace std; class TestClass { string ClassName; public: TestClass(string Name) { ClassName = Name; cout << ClassName << " constructed." << endl; } ~TestClass() { cout << ClassName << " destructed." << endl; } void operator=(TestClass Other) { cout << ClassName << " in operator=" << endl; cout << "The address of the other class is " << &Other << "." << endl; } }; int main() { TestClass FirstInstance("FirstInstance"); TestClass SecondInstance("SecondInstance"); FirstInstance = SecondInstance; SecondInstance = FirstInstance; return 0; } The assignment operator behaves as-expected, outputting the address of the other class. Now, how would I actually assign something from the other class? For example, something like this: void operator=(TestClass Other) { ClassName = Other.ClassName; }

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• Cannot write the output to a text file in cpp program

  - by swapedoc

  I have this input file "https://code.google.com/codejam/contest/351101/dashboard/do/A-large-practice.in?cmd=GetInputFile&problem=374101&input_id=1&filename=A-large-practice.in&redownload_last=1&agent=website&csrfmiddlewaretoken=OWMxNTVmMTUyODBiYjhhN2Q2OTM3ZGJiMTNhNDkwMDF8fDEzNzIxNzI1NTE3ODAzMjA%3D" I tried to read this file :-using freopen("filename.txt",r,stdin); and then I wanted the output written to be written to another text file which I can upload in this codejam practice question for the judge. #include<iostream> #include<cstdio> using namespace std; int main() { int t,k=0,a[2000]; freopen("ab.txt","r",stdin); scanf("%d",&t); while(t--) { freopen("cb.txt","w",stdout); int c; scanf("%d",&c); int n; scanf("%d",&n); for(int i=0;i<n;i++) scanf("%d",&a[i]); printf("Case #%d: ",++k); for(int i=0;i<n-1;i++) {for(int j=i+1;j<n;j++) if((a[i]+a[j])==c) {printf("%d %d\n",i+1,j+1); i=n;} } } return 0; } This is my code. Now the problem is the output file cb.txt contains only the last line of the input. I want the the whole of the output to be written to cb.txt,so what should I do.

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• Xerces C++ SAX Parsing Problem: expected class-name before '{' token

  - by aduric

  I'm trying to run through an example given for the C++ Xerces XML library implementation. I've copied the code exactly, but I'm having trouble compiling it. error: expected class-name before '{' token I've looked around for a solution, and I know that this error can be caused by circular includes or not defining a class before it is used, but as you can see from the code, I only have 2 files: MySAXHandler.hpp and MySAXHandler.cpp. However, the MySAXHandler class is derived from HandlerBase, which is included. MyHandler.hpp #include <xercesc/sax/HandlerBase.hpp> class MySAXHandler : public HandlerBase { public: void startElement(const XMLCh* const, AttributeList&); void fatalError(const SAXParseException&); }; MySAXHandler.cpp #include "MySAXHandler.hpp" #include <iostream> using namespace std; MySAXHandler::MySAXHandler() { } void MySAXHandler::startElement(const XMLCh* const name, AttributeList& attributes) { char* message = XMLString::transcode(name); cout << "I saw element: "<< message << endl; XMLString::release(&message); } void MySAXHandler::fatalError(const SAXParseException& exception) { char* message = XMLString::transcode(exception.getMessage()); cout << "Fatal Error: " << message << " at line: " << exception.getLineNumber() << endl; XMLString::release(&message); } I'm compiling like so: g++ -L/usr/local/lib -lxerces-c -I/usr/local/include -c MySAXHandler.cpp I've looked through the HandlerBase and it is defined, so I don't know why I can't derive a class from it? Do I have to override all the virtual functions in HandlerBase? I'm kinda new to C++. Thanks in advance.

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• Boost link error when using "--layout=system" on VS2005

  - by Kevin

  I'm new to boost, and thought I'd try it out with some realistic deployment scenarios for the .dlls, so I used the following command to compile/install the libraries: .\bjam install --layout=system variant=debug runtime-link=shared link=shared --with-date_time --with-thread --with-regex --with-filesystem --includedir=<my include directory> --libdir=<my bin directory> > installlog.txt That seemed to work, but my simple program (taken right from the "Getting Started" page) fails: #include <boost/regex.hpp> #include <iostream> #include <string> // Place your functions after this line int main() { std::string line; boost::regex pat( "^Subject: (Re: |Aw: )*(.*)" ); while (std::cin) { std::getline(std::cin, line); boost::smatch matches; if (boost::regex_match(line, matches, pat)) std::cout << matches[2] << std::endl; } } This fails with the following linker error: fatal error LNK1104: cannot open file 'libboost_regex-vc80-mt-1_42.lib' I'm sure that both the .lib and the .dlls are in that directory, and named how I want them to be (ie: boost_regex.lib, etc, all unversioned, as the --layout=system says). So why is it looking for the versioned type of it? And how do I get it to look for the unversioned type of the library? I've tried this with more "normal" options, such as below: .\bjam stage --build-type=complete --with-date_time --with-thread --with-filesystem --with-regex > mybuildlog.txt And that works fine. I made sure my compiler saw the "stage\lib" directory, and it compiled and ran fine with nothing beyond having the environment looking into the right lib directory. But when I took those "testing" directories away, and wanted to use these others (unversioned), then it failed. I'm under VS2005 here on XP. Any ideas?

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• Queue Data structure app crash with front() method

  - by Programer

  I am implementing queue data strcutre but my app gets crashed, I know I am doing something wrong with Node pointer front or front() method of queue class #include <iostream> using namespace std; class Node { public: int get() { return object; }; void set(int object) { this->object = object; }; Node * getNext() { return nextNode; }; void setNext(Node * nextNode) { this->nextNode = nextNode; }; private: int object; Node * nextNode; }; class queue{ private: Node *rear; Node *front; public: int dequeue() { int x = front->get(); Node* p = front; front = front->getNext(); delete p; return x; } void enqueue(int x) { Node* newNode = new Node(); newNode->set(x); newNode->setNext(NULL); rear->setNext(newNode); rear = newNode; } int Front() { return front->get(); } int isEmpty() { return ( front == NULL ); } }; main() { queue q; q.enqueue(2); cout<<q.Front(); system("pause"); }

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• Output is different for R-value and L-value. Why?

  - by Leonid Volnitsky

  Can someone explain to me why output for R-value is different from L-value? #include <iostream> #include <vector> using namespace std; template<typename Ct> struct ct_wrapper { Ct&& ct; // R or L ref explicit ct_wrapper(Ct&& ct) : ct(std::forward<Ct>(ct)) { std::cout << this->ct[1];}; }; int main() { // L-val vector<int> v{1,2,3}; ct_wrapper<vector<int>&> lv(v); cout << endl << lv.ct[0] << lv.ct[1] << lv.ct[2] << endl; // R-val ct_wrapper<vector<int>&&> rv(vector<int>{1,2,3}); cout << endl << rv.ct[0] << rv.ct[1] << rv.ct[2] << endl; } Output (same for gcc48 and clang32): 2 123 2 003

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• OpenGL Nothing will Display

  - by m00st

  Why can't I get anything to display with this code? #include <iostream> #include "GL/glfw.h" #ifndef MAIN #define MAIN #include "GL/gl.h" #include "GL/glu.h" #endif using namespace std; void display(); int main() { int running = GL_TRUE; glfwInit(); if( !glfwOpenWindow( 640,480, 0,0,0,0,0,0, GLFW_WINDOW ) ) { glfwTerminate(); return 0; } while( running ) { //GL Code here display(); glfwSwapBuffers(); // Check if ESC key was pressed or window was closed running = !glfwGetKey( GLFW_KEY_ESC ) && glfwGetWindowParam( GLFW_OPENED ); } glfwTerminate(); return 0; } void display() { glClearColor(0, 0,0, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glLoadIdentity(); gluLookAt(0, 0, 5, 0.0, 0.0, 0.0, 0, 1, 0); glScalef(1.0f, 1.0f, 1.0f); glTranslatef(0, 0, -2); glBegin(GL_POLYGON); glColor3f(1.0, 0.2, 0.2); glVertex3f(0.25, 0.25, 0.0); glVertex3f(0.75, 0.25, 0.0); glVertex3f(0.75, 0.75, 0.0); glVertex3f(0.25, 0.75, 0.0); glEnd(); glFlush(); }

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• Programming help Loop adding

  - by Deonna

  I know this probably really simple but Im not sure what im doing wrong... The assignment states: For the second program for this lab, you are to have the user enter an integer value in the range of 10 to 50. You are to verify that the user enters a value in that range, and continue to prompt him until he does give you a value in that range. After the user has successfully entered a value in that range, you are to display the sum of all the integers from 1 to the value entered. I have this so far: #include <iostream.h> int main () { int num, sum; cout << "do-while Loop Example 2" << endl << endl; do { cout << "Enter a value from 10 to 50: "; cin >> num; if (num < 10 || num > 50) cout << "Out of range; Please try again..." << endl; } while (num < 10 || num > 50); { int i; int sum = 0; for (num = 1; num <= 50; num ++) sum = sum + num; } cout << endl << "The sum is " << sum << endl; return 0; } Im just not sure exactly what i'm doing wrong... I keep getting the wrong sum for the total...

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• How to use dirent.h correctly.

  - by Nick

  Hello, I am new to C++ and I am experimenting with the dirent.h header to manipulate directory entries. The following little app compiles but pukes after you supple a directory name. Can someone give me a hint? The int quit is there to provide a while loop. I removed the loop in an attempt to isolate my problem. thanks! #include <iostream> #include <dirent.h> using namespace std; int main() { char *dirname = 0; DIR *pd = 0; struct dirent *pdirent = 0; int quit = 1; cout<< "Enter a directory path to open (leave blank to quit):\n"; cin >> dirname; if(dirname == NULL) { quit = 0; } pd = opendir(dirname); if(pd == NULL) { cout << "ERROR: Please provide a valid directory path.\n"; } return 0; }

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• Reading strings and integers from .txt file and printing output as strings only

  - by screename71

  Hello, I'm new to C++, and I'm trying to write a short C++ program that reads lines of text from a file, with each line containing one integer key and one alphanumeric string value (no embedded whitespace). The number of lines is not known in advance, (i.e., keep reading lines until end of file is reached). The program needs to use the 'std::map' data structure to store integers and strings read from input (and to associate integers with strings). The program then needs to output string values (but not integer values) to standard output, 1 per line, sorted by integer key values (smallest to largest). So, for example, suppose I have a text file called "data.txt" which contains the following three lines: 10 dog -50 horse 0 cat -12 zebra 14 walrus The output should then be: horse zebra cat dog walrus I've pasted below the progress I've made so far on my C++ program: #include <fstream> #include <iostream> #include <map> using namespace std; using std::map; int main () { string name; signed int value; ifstream myfile ("data.txt"); while (! myfile.eof() ) { getline(myfile,name,'\n'); myfile >> value >> name; cout << name << endl; } return 0; myfile.close(); } Unfortunately, this produces the following incorrect output: horse cat zebra walrus If anyone has any tips, hints, suggestions, etc. on changes and revisions I need to make to the program to get it to work as needed, can you please let me know? Thanks!

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• C++ function overloading and dynamic binding compile problem

  - by Olorin

  #include <iostream> using namespace std; class A { public: virtual void foo(void) const { cout << "A::foo(void)" << endl; } virtual void foo(int i) const { cout << i << endl; } virtual ~A() {} }; class B : public A { public: void foo(int i) const { this->foo(); cout << i << endl; } }; class C : public B { public: void foo(void) const { cout << "C::foo(void)" << endl; } }; int main(int argc, char ** argv) { C test; test.foo(45); return 0; } The above code does not compile with: $>g++ test.cpp -o test.exe test.cpp: In member function 'virtual void B::foo(int) const': test.cpp:17: error: no matching function for call to 'B::foo() const' test.cpp:17: note: candidates are: virtual void B::foo(int) const test.cpp: In function 'int main(int, char**)': test.cpp:31: error: no matching function for call to 'C::foo(int)' test.cpp:23: note: candidates are: virtual void C::foo() const It compiles if method "foo(void)" is changed to "goo(void)". Why is this so? Is it possible to compile the code without changing the method name of "foo(void)"? Thanks.

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• How do I build a filtered_streambuf based on basic_streambuf?

  - by swestrup

  I have a project that requires me to insert a filter into a stream so that outgoing data will be modified according to the filter. After some research, it seems that what I want to do is create a filtered_streambuf like this: template <class StreamBuf class filtered_streambuf: public StreamBuf { ... } And then insert a filtered_streambuf<> into whichever stream I need to be filtered. My problem is that I don't know what invariants I need to maintain while filtering a stream, in order to ensure that Derived classes can work as expected. In particular, I may find I have filtered_streambufs built over other filtered_streambufs. All the various stream inserters, extractors and manipulators work as expected. The trouble is that I just can't seem to work out what the minimal interface is that I need to supply in order to guarantee that an iostream will have what it needs to work correctly. In particular, do I need to fake the movement of the protected pointer variables, or not? Do I need a fake data buffer, or not? Can I just override the public functions, rewriting them in terms of the base streambuf, or is that too simplistic?

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• Usage of VIsual Memory Leak Detector

  - by Yan Cheng CHEOK

  I found a very interesting memory leak detector by using Visual C++. http://www.codeproject.com/KB/applications/visualleakdetector.aspx I try it out, but cannot make it works to detect a memory leak code. I am using MS Visual Studio 2008. Any step I had missed out? #include "stdafx.h" #include "vld.h" #include <iostream> void fun() { new int[1000]; } int _tmain(int argc, _TCHAR* argv[]) { fun(); std::cout << "lead?" << std::endl; getchar(); return 0; } The output when I run in debug mode is : ... ... 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC80.CRT_1fc8b3b9a1e18e3b_8.0.50727.4053_x-ww_e6967989\msvcr80.dll', Symbols loaded. 'Test.exe': Loaded 'C:\WINDOWS\system32\msvcrt.dll', Symbols loaded (source information stripped). 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC90.DebugCRT_1fc8b3b9a1e18e3b_9.0.30729.1_x-ww_f863c71f\msvcp90d.dll', Symbols loaded. 'Test.exe': Loaded 'C:\Program Files\Visual Leak Detector\bin\dbghelp.dll', Symbols loaded (source information stripped). Visual Leak Detector Version 1.9d installed. No memory leaks detected. Visual Leak Detector is now exiting. The program '[5468] Test.exe: Native' has exited with code 0 (0x0).

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• base destructor called twice after derived object?

  - by sil3nt

  hey there, why is the base destructor called twice at the end of this program? #include <iostream> using namespace std; class B{ public: B(){ cout << "BC" << endl; x = 0; } virtual ~B(){ cout << "BD" << endl; } void f(){ cout << "BF" << endl; } virtual void g(){ cout << "BG" << endl; } private: int x; }; class D: public B{ public: D(){ cout << "dc" << endl; y = 0; } virtual ~D(){ cout << "dd" << endl; } void f(){ cout << "df" << endl; } virtual void g(){ cout << "dg" << endl; } private: int y; }; int main(){ B b, * bp = &b; D d, * dp = &d; bp->f(); bp->g(); bp = dp; bp->f(); bp->g(); }

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• How do you search a document for a string in c++?

  - by Jeff

  Here's my code so far: #include<iostream> #include<string> #include<fstream> using namespace std; int main() { int count = 0; string fileName; string keyWord; string word; cout << "Please make sure the document is in the same file as the program, thank you!" << endl << "Please input document name: " ; getline(cin, fileName); cout << endl; cout << "Please input the word you'd like to search for: " << endl; cin >> keyWord; cout << endl; ifstream infile(fileName.c_str()); while(infile.is_open()) { getline(cin,word); if(word == keyWord) { cout << word << endl; count++; } if(infile.eof()) { infile.close(); } } cout << count; } I'm not sure how to go to the next word, currently this infinite loops...any recommendation? Also...how do I tell it to print out the line that that word was on? Thanks in advance!

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• Difference in behaviour( gcc and MSVC++ )

  - by Prasoon Saurav

  Consider the following code. #include <stdio.h> #include <vector> #include <iostream> struct XYZ { int X,Y,Z; }; std::vector<XYZ> A; int rec(int idx) { int i = A.size(); A.push_back(XYZ()); if (idx >= 5) return i; A[i].X = rec(idx+1); return i; } int main(){ A.clear(); rec(0); puts("FINISH!"); } I couldn't figure out the reason why the code gives segmentation fault on Linux(IDE used: Code::Blocks) whereas on Windows(IDE used : MSVC++) it doesn't. When I used valgrind just to check what actually the problem was, I got this output. I got Invalid write of size 4 at four different places. Then why didn't the code crash when I used MSVC++? Am I missing something?

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• Question about Virtual Inheritance hierarchy

  - by Summer_More_More_Tea

  Hi there: I encounter this problem when tackling with virtual inheritance. I remember that in a non-virtual inheritance hierarchy, object of sub-class hold an object of its direct super-class. What about virtual inheritance? In this situation, does object of sub-class hold an object of its super-class directly or just hold a pointer pointing to an object of its super-class? By the way, why the output of the following code is: sizeof(A): 8 sizeof(B): 20 sizeof(C): 20 sizeof(C): 36 Code: #include <iostream> using namespace std; class A{ char k[ 3 ]; public: virtual void a(){}; }; class B : public virtual A{ char j[ 3 ]; public: virtual void b(){}; }; class C : public virtual B{ char i[ 3 ]; public: virtual void c(){}; }; class D : public B, public C{ char h[ 3 ]; public: virtual void d(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; cout << "sizeof(D): " << sizeof( D ) << endl; return 0; } Thanks in advance. Kind regards.

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