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  • C++ Suppress Automatic Initialization and Destruction

    - by Travis G
    How does one suppress the automatic initialization and destruction of a type? While it is wonderful that T buffer[100] automatically initializes all the elements of buffer, and destroys them when they fall out of scope, this is not the behavior I want. #include <iostream> static int created = 0, destroyed = 0; struct S { S() { ++created; } ~S() { ++destroyed; } }; template <typename T, size_t KCount> class Array { private: T m_buffer[KCount]; public: Array() { // some way to suppress the automatic initialization of m_buffer } ~Array() { // some way to suppress the automatic destruction of m_buffer } }; int main() { { Array<S, 100> arr; } std::cout << "Created:\t" << created << std::endl; std::cout << "Destroyed:\t" << destroyed << std::endl; return 0; } The output of this program is: Created: 100 Destroyed: 100 I would like it to be: Created: 0 Destroyed: 0 My only idea is to make m_buffer some trivially constructed and destructed type like char and then rely on operator[] to wrap the pointer math for me, although this seems like a horribly hacked solution. Another solution would be to use malloc and free, but that gives a level of indirection that I do not want.

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  • Are C++ exceptions sufficient to implement thread-local storage?

    - by Potatoswatter
    I was commenting on an answer that thread-local storage is nice and recalled another informative discussion about exceptions where I supposed The only special thing about the execution environment within the throw block is that the exception object is referenced by rethrow. Putting two and two together, wouldn't executing an entire thread inside a function-catch-block of its main function imbue it with thread-local storage? It seems to work fine: #include <iostream> #include <pthread.h> using namespace std; struct thlocal { string name; thlocal( string const &n ) : name(n) {} }; thlocal &get_thread() { try { throw; } catch( thlocal &local ) { return local; } } void print_thread() { cerr << get_thread().name << endl; } void *kid( void *local_v ) try { thlocal &local = * static_cast< thlocal * >( local_v ); throw local; } catch( thlocal & ) { print_thread(); return NULL; } int main() try { thlocal local( "main" ); throw local; } catch( thlocal & ) { print_thread(); pthread_t th; thlocal kid_local( "kid" ); pthread_create( &th, NULL, &kid, &kid_local ); pthread_join( th, NULL ); print_thread(); return 0; } Is this novel or well-characterized? Was my initial premise correct? What kind of overhead does get_thread incur in, say, GCC and VC++? It would require throwing only exceptions derived from struct thlocal, but altogether this doesn't feel like an unproductive insomnia-ridden Sunday morning…

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  • C++ program crashes at runtime

    - by qwerty
    Hello, I have this simple c++ program #include <cstdlib> #include <iostream> #include <math.h> #include <stdlib.h> #include <time.h> #include <vector> using namespace std; int aleator(int n) { return (rand()%n)+1; } int main() { int r; int indexes[100]={0}; // const int size=100; //int a[size]; std::vector<int>v; srand(time(0)); for (int i=0;i<25;i++) { int index = aleator(100); if (indexes[index] != 0) { // try again i--; continue; } indexes[index] = 1; cout << v[index] ; } cout<<" "<<endl; system("pause"); return 0; } But at runtime it crashes, so i got that error with 'Send error report' and 'Don't send'. What i'm doing wrong? Thanks!

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  • C++ Loop - Need variable to accumulate sum

    - by user1780064
    I'm writing a program to ask the user to enter a value between 5 and 21 (inclusive). If the number entered is not in this range, it prints, "Please try again". If the number is within the range, I need to take that number, and print the sum of all the numbers from 1 to the value entered. So if the user entered "7", the sum would be "28". I successfully wrote the first loop, in the case of the number not being within the range, but cannot figure out how to run the second loop- whether to use a while, do-while, or for loop. Please advise. #include <iostream> int main () { int uservalue; int count; int sum; //Prompt user for input do { cout << "Enter a value from 5 to 21: "; cin >> uservalue; if (uservalue < 5 || uservalue > 21) cout << "Value out of range. Try again..." << endl; } while (uservalue < 5 || uservalue > 21); cout << endl; //Loop to accumulate sum for (count = 1, count < uservalue, count++;) { sum = uservalue + count; if (uservalue <= 5 || uservalue <= 21) cout << the sum is " << sum << endl; } return 0; }

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  • give feedback on this pointer program

    - by JohnWong
    This is relatively simple program. But I want to get some feedback about how I can improve this program (if any), for example, unnecessary statements? #include<iostream> #include<fstream> using namespace std; double Average(double*,int); int main() { ifstream inFile("data2.txt"); const int SIZE = 4; double *array = new double(SIZE); double *temp; temp = array; for (int i = 0; i < SIZE; i++) { inFile >> *array++; } cout << "Average is: " << Average(temp, SIZE) << endl; } double Average(double *pointer, int x) { double sum = 0; for (int i = 0; i < x; i++) { sum += *pointer++; } return (sum/x); } The codes are valid and the program is working fine. But I just want to hear what you guys think, since most of you have more experience than I do (well I am only a freshman ... lol) Thanks.

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  • how do i save time to a file?

    - by blood
    hi, i have a program that saves data to file and i want to put a time stamp of the current date/time on that log but when i try to write the time to the file it will not show up. #include <iostream> #include <windows.h> #include <fstream> #include <string> #include <sstream> #include <direct.h> #include <stdio.h> #include <time.h> using namespace std; string header_str = ("NULL"); int main() { for(;;) { stringstream header(stringstream::in | stringstream::out); header << "datasdasdasd_"; time_t rawtime; time ( &rawtime ); header << ctime (&rawtime); header_str = header.str(); fstream filestr; filestr.open ("C:\\test.txt", fstream::in | fstream::out | fstream::app | ios_base::binary | ios_base::out); for(;;) { filestr << (header_str); } filestr.close(); } return 0; } anyone know how to fix this?

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  • Proper QUuid usage in Qt ? (7-Zip DLL usage problems (QLibrary, QUuid GUID conversion, interfaces))

    - by whipsnap
    Hi, I'm trying to write a program that would use 7-Zip DLL for reading files from inside archive files (7z, zip etc). Here's where I'm so far: #include QtCore/QCoreApplication #include QLibrary #include QUuid #include iostream using namespace std; #include "7z910/CPP/7zip/Archive/IArchive.h" #include "7z910/CPP/7zip/IStream.h" #include "MyCom.h" // {23170F69-40C1-278A-1000-000110070000} QUuid CLSID_CFormat7z(0x23170F69, 0x40C1, 0x278A, 0x10, 0x00, 0x00, 0x01, 0x10, 0x07, 0x00, 0x00); typedef int (*CreateObjectFunc)( const GUID *clsID, const GUID *interfaceID, void **outObject); void readFileInArchive() { QLibrary myLib("7z.dll"); CreateObjectFunc myFunction = (CreateObjectFunc)myLib.resolve("CreateObject"); if (myFunction == 0) { cout outArchive; myFunction(&CLSID_CFormat7z, &IID_IOutArchive, (void **)&outArchive); } int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); readFileInArchive(); return a.exec(); } Trying to build that in Qt Creator will lead to following error: cannot convert 'QUuid*' to 'const GUID*' in argument passing How should QUuid be correctly used in this context? Also, being a C++ and Qt newbie I haven't yet quite grasped templates or interfaces, so overall I'm having trouble getting through these first steps. If someone could give tips or even example code on how for example an image file could be extracted from ZIP file (to be shown in Qt GUI later on*), I would highly appreciate that. My main goal at the moment is to write a program with GUI for selecting archive files containing image files (PNG, JPG etc) and displaying those files one at a time in the GUI. A Qt based CDisplayEx in short.

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  • Segmentation fault on returning from main (very short and simple code, no arrays or pointers)

    - by Gábor Kovács
    I've been wondering why the following trivial code produces a segmentation fault when returning from main(): //Produces "Error while dumping state (probably corrupted stack); Segmentation fault" #include <iostream> #include <fstream> #include <vector> using namespace std; class Test { vector<int> numbers; }; int main() { Test a; ifstream infile; cout << "Last statement..." << endl; // this gets executed return 0; } Interestingly, 1) if only one of the two variables is declared, I don't get the error, 2) if I declare a vector variable instead of an object with a vector member, everything's fine, 3) if I declare an ofstream instead of an ifstream, again, everything works fine. Something appears to be wrong with this specific combination... Could this be a compiler bug? I use gcc version 3.4.4 with cygwin. Thanks for the tips in advance. Gábor

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  • Why does this code leak? (simple codesnippet)

    - by Ela782
    Visual Studio shows me several leaks (a few hundred lines), in total more than a few MB. I traced it down to the following "helloWorld example". The leak disappears if I comment out the H5::DataSet.getSpace() line. #include "stdafx.h" #include <iostream> #include "cpp/H5Cpp.h" int main(int argc, char *argv[]) { _CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF ); // dump leaks at return H5::H5File myfile; try { myfile = H5::H5File("C:\\Users\\yyy\\myfile.h5", H5F_ACC_RDONLY); } catch (H5::Exception& e) { std::string msg( std::string( "Could not open HDF5 file.\n" ) + e.getCDetailMsg() ); throw msg; } H5::Group myGroup = myfile.openGroup("/so/me/group"); H5::DataSet myDS = myGroup.openDataSet("./myfloatvec"); hsize_t dims[1]; //myDS.getSpace().getSimpleExtentDims(dims, NULL); // <-- here's the leak H5::DataSpace dsp = myDS.getSpace(); // The H5::DataSpace seems to leak dsp.getSimpleExtentDims(dims, NULL); //dsp.close(); // <-- doesn't help either std::cout << "Dims: " << dims[0] << std::endl; // <-- Works as expected return 0; } Any help would be appreciated. I've been on this for hours, I hate unclean code...

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  • UnauthorizedAccessException when running desktop application from shared folder

    - by Atara
    I created a desktop application using VS 2008. When I run it locally, all works well. I shared my output folder (WITHOUT allowing network users to change my files) and ran my exe from another Vista computer on our intranet. When running the shared exe, I receive "System.UnauthorizedAccessException" when trying to read a file. How can I give permission to allow reading the file? Should I change the code? Should I grant permission to the application\folder on the Vista computer? how? Notes: I do not use ClickOnce. the application should be distributed using xcopy. My application target framework is ".Net Framework 2.0" On the Vista computer, "controlPanel | UninstallOrChangePrograms" it says it has "Microsoft .Net Framework 3.5 SP1" I also tried to map the folder drive, but got the same errors, only now the fileName is "T:\my.ocx" ' ---------------------------------------------------------------------- ' my code: Dim src As String = mcGlobals.cmcFiles.mcGetFileNameOcx() Dim ioStream As New System.IO.FileStream(src, IO.FileMode.Open) ' ---------------------------------------------------------------------- Public Shared Function mcGetFileNameOcx() As String ' ---------------------------------------------------------------------- Dim dirName As String = Application.StartupPath & "\" Dim sFiles() As String = System.IO.Directory.GetFiles(dirName, "*.ocx") Dim i As Integer For i = 0 To UBound(sFiles) Debug.WriteLine(System.IO.Path.GetFullPath(sFiles(i))) ' if found any - return the first: Return System.IO.Path.GetFullPath(sFiles(i)) Next Return "" End Function ' ---------------------------------------------------------------------- ' The Exception I receive: System.UnauthorizedAccessException: Access to the path '\\computerName\sharedFolderName\my.ocx' is denied. at System.IO._Error(Int32 errorCode, String maybeFullPath) at System.IO.FileStream.Init(...) at System.IO.FileStream..ctor(...) at System.IO.FileStream..ctor(String path, FileMode mode) ' ----------------------------------------------------------------------

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  • Getting functions of inherited functions to be called

    - by wrongusername
    Let's say I have a base class Animal from which a class Cow inherits, and a Barn class containing an Animal vector, and let's say the Animal class has a virtual function scream(), which Cow overrides. With the following code: Animal.h #ifndef _ANIMAL_H #define _ANIMAL_H #include <iostream> using namespace std; class Animal { public: Animal() {}; virtual void scream() {cout << "aaaAAAAAAAAAAGHHHHHHHHHH!!! ahhh..." << endl;} }; #endif /* _ANIMAL_H */ Cow.h #ifndef _COW_H #define _COW_H #include "Animal.h" class Cow: public Animal { public: Cow() {} void scream() {cout << "MOOooooOOOOOOOO!!!" << endl;} }; #endif /* _COW_H */ Barn.h #ifndef _BARN_H #define _BARN_H #include "Animal.h" #include <vector> class Barn { std::vector<Animal> animals; public: Barn() {} void insertAnimal(Animal animal) {animals.push_back(animal);} void tortureAnimals() { for(int a = 0; a < animals.size(); a++) animals[a].scream(); } }; #endif /* _BARN_H */ and finally main.cpp #include <stdlib.h> #include "Barn.h" #include "Cow.h" #include "Chicken.h" /* * */ int main(int argc, char** argv) { Barn barn; barn.insertAnimal(Cow()); barn.tortureAnimals(); return (EXIT_SUCCESS); } I get this output: aaaAAAAAAAAAAGHHHHHHHHHH!!! ahhh... How should I code this to get MOOooooOOOOOOOO!!! (and whatever other classes inheriting Animal wants scream() to be) instead?

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  • Friends, templates, overloading <<

    - by Crystal
    I'm trying to use friend functions to overload << and templates to get familiar with templates. I do not know what these compile errors are: Point.cpp:11: error: shadows template parm 'class T' Point.cpp:12: error: declaration of 'const Point<T>& T' for this file #include "Point.h" template <class T> Point<T>::Point() : xCoordinate(0), yCoordinate(0) {} template <class T> Point<T>::Point(T xCoordinate, T yCoordinate) : xCoordinate(xCoordinate), yCoordinate(yCoordinate) {} template <class T> std::ostream &operator<<(std::ostream &out, const Point<T> &T) { std::cout << "(" << T.xCoordinate << ", " << T.yCoordinate << ")"; return out; } My header looks like: #ifndef POINT_H #define POINT_H #include <iostream> template <class T> class Point { public: Point(); Point(T xCoordinate, T yCoordinate); friend std::ostream &operator<<(std::ostream &out, const Point<T> &T); private: T xCoordinate; T yCoordinate; }; #endif My header also gives the warning: Point.h:12: warning: friend declaration 'std::ostream& operator<<(std::ostream&, const Point<T>&)' declares a non-template function Which I was also unsure why. Any thoughts? Thanks.

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  • Cannot compute equation, always gives zero

    - by user1738391
    Did i miss something? The variable percentage_ always equals 0. I've checked nTimes and winnings, they give the correct values as what is being input. Even when I test out a simple equation like, percentage_=1+1, percentage_ will give 0. Can someone help? #pragma once #include <iostream> #include <string> #include <cstdlib> #include <iomanip> using namespace std; class GuessMachine { private: int nTimes; int winnings; string nM[6]; public: GuessMachine(); void displayPrizes(); void displayMenu(); int getInput(); void checkNumber(); void checkPrize(); }; void GuessMachine::checkPrize() { MagicNumber mn; int prize_=mn.generateNumber(); float percentage_; percentage_ = float (winnings/nTimes*100); //<--On this line percentage is always 0 no matter what winnings and nTimes are cout<<"Percentage is "<<percentage_<<endl; if(percentage_ >= 50) { cout<<"You have scored "<<percentage_<<"% and won "<<nM[prize_]; } else { cout<<"You have scored "<<percentage_<<"%. You lose!!"; } cin.ignore(); cin.ignore(); }

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  • Why is it that an int in C++ that isnt initialized (then used) doesn't return an error?

    - by omizzle
    I am new to C++ (just starting). I come from a Java background and I was trying out the following piece of code that would sum the numbers between 1 and 10 (inclusive) and then print out the sum: /* * File: main.cpp * Author: omarestrella * * Created on June 7, 2010, 8:02 PM */ #include <cstdlib> #include <iostream> using namespace std; int main() { int sum; for(int x = 1; x <= 10; x++) { sum += x; } cout << "The sum is: " << sum << endl; return 0; } When I ran it it kept printing 32822 for the sum. I knew the answer was supposed to be 55 and realized that its print the max value for a short (32767) plus 55. Changing int sum; to int sum = 0; would work (as it should, since the variable needs to be initialized!). Why does this behavior happen, though? Why doesnt the compiler warn you about something like this? I know Java screams at you when something isnt initialized. Thank you.

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  • Segmentation Fault when trying to push a string to the back of a list.

    - by user308012
    I am trying to write a logger class for my C++ calculator, but I'm experiencing a problem while trying to push a string into a list. I have tried researching this issue and have found some information on this, but nothing that seems to help with my problem. I am using a rather basic C++ compiler, with little debugging utilities and I've not used C++ in quite some time (even then it was only a small amount). My code: #ifndef _LOGGER_H_ #define _LOGGER_H_ #include <iostream> #include <list> #include <string> using std::cout; using std::cin; using std::endl; using std::list; using std::string; class Logger { private: list<string> *mEntries; public: Logger() { // Initialize the entries list mEntries = new list<string>(); } ~Logger() { // Release the list mEntries->clear(); delete mEntries; } // Public Methods void WriteEntry(string entry) { // *** BELOW LINE IS MARKED WITH THE ERROR *** mEntries->push_back(string(entryData)); } void DisplayEntries() { cout << endl << "**********************" << endl << "* Logger Entries *" << endl << "**********************" << endl << endl; for(list<string>::iterator it = mEntries->begin(); it != mEntries->end(); it++) { cout << *it << endl; } } }; #endif I am calling the WriteEntry method by simply passing in a string, like so: mLogger->WriteEntry("Testing"); Any advice on this would be greatly appreciated.

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  • Returning reference to object is not changing the address in c++

    - by ashish-sangwan
    I am trying to understand functions returning a reference. For that I have written a simple program: #include<iostream> using namespace std; class test { int i; friend test& func(); public: test(int j){i=j;} void show(){cout<<i<<endl;} }; test& func() { test temp(10); return temp; //// Address of temp=0xbfcb2874 } int main() { test obj1(50); // Address of obj1=0xbfcb28a0 func()=obj1; <= Problem:The address of obj1 is not changing obj1.show(); // // Address of obj1=0xbfcb28a0 return 0; } I ran the program using gdb and observed that the address of obj1 still remains same, but I expect it to get changed to 0xbfcb2874. I am not clear with the concept. Please help.

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  • Segmentation fault on instationation of more than 1 object

    - by ECE
    I have a class called "Vertex.hpp" which is as follows: #include <iostream> #include "Edge.hpp" #include <vector> using namespace std; /** A class, instances of which are nodes in an HCTree. */ class Vertex { public: Vertex(char * str){ *name=*str; } vector<Vertex*> adjecency_list; vector<Edge*> edge_weights; char *name; }; #endif When I instantiate an object of type Vector as follows: Vertex *first_read; Vertex *second_read; in.getline(input,256); str=strtok(input," "); first_read->name=str; str=strtok(NULL, " "); second_read->name=str; A segmentation fault occurs when more than 1 object of type Vector is instantiated. Why would this occur if more than 1 object is instantiated, and how can i allow multiple objects to be instantiated?

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  • Reverse String Error?

    - by R41nB0w M47r1z
    I am creating this revese string App but i get a error if i include a space in the string ! #include <iostream> #include <string> using namespace std; int main() { int inputa; cout<<"%%%%%%%%%%%%%%%%%%String Reversing App%%%%%%%%%%%%%%%%%%%%%%%%"<<endl<<endl; cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl; cin>>inputa; if(inputa!=0) { do { string a,c=""; cout<<"\nEnter the string you want to Reverse : "; cin>>a; for(int x=a.length()-1; x>=0; x--) { c=c+a.substr(x,1); } cout<<"\nThe Reverse String is : "<<c<<endl; cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl; cin>>inputa; } while(inputa!=0); } //not my home work } If I type the following string like "abc def" there i get an error . But otherwise it works perfectly ! Is there some mistake with the codes ! I am new to CPP so it would be helpful if you could help me !

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  • C++ destructor problem with boost::scoped_ptr

    - by bb-generation
    I have a question about the following code: #include <iostream> #include <boost/scoped_ptr.hpp> class Interface { }; class A : public Interface { public: A() { std::cout << "A()" << std::endl; } virtual ~A() { std::cout << "~A()" << std::endl; } }; Interface* get_a() { A* a = new A; return a; } int main() { { std::cout << "1" << std::endl; boost::scoped_ptr<Interface> x(get_a()); std::cout << "2" << std::endl; } std::cout << "3" << std::endl; } It creates the following output: 1 A() 2 3 As you can see, it doesn't call the destructor of A. The only way I see to get the destructor of A being called, is to add a destructor for the Interface class like this: virtual ~Interface() { } But I really want to avoid any Implementation in my Interface class and virtual ~Interface() = 0; doesn't work (produces some linker errors complaining about a non existing implementation of ~Interface(). So my question is: What do I have to change in order to make the destructor being called, but (if possible) leave the Interface as an Interface (only abstract methods).

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  • overloading "<<" with a struct (no class) cout style

    - by monkeyking
    I have a struct that I'd like to output using either 'std::cout' or some other output stream. Is this possible without using classes? Thanks #include <iostream> #include <fstream> template <typename T> struct point{ T x; T y; }; template <typename T> std::ostream& dump(std::ostream &o,point<T> p) const{ o<<"x: " << p.x <<"\ty: " << p.y <<std::endl; } template<typename T> std::ostream& operator << (std::ostream &o,const point<T> &a){ return dump(o,a); } int main(){ point<double> p; p.x=0.1; p.y=0.3; dump(std::cout,p); std::cout << p ;//how? return 0; } I tried different syntax' but I cant seem to make it work.

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  • Simple C++ code (what's wrong here?)

    - by JW
    Noob to C++. I'm trying to get user input (Last Name, First Name Middle Name), change part of it (Middle Name to Middle Initial) and then rearrange it (First Middle Initial Last). Where am I messing up in my code? --Thanks for ANY help you can offer! ... #include <iostream> using std::cout; using std::cin; #include <string> using std::string; int main() { string myString, last, first, middle; cout << "Enter your name: Last, First Middle"; cin >> last >> first >> middle; char comma, space1, space2; comma = myString.find_first_of(','); space1 = myString.find_first_of(' '); space2 = myString.find_last_of(' '); last = myString.substr (0, comma); // user input last name first = myString.substr (space1+1, -1); // user input first name middle = myString.substr (space2+1, -1); // user input middle name middle.insert (0, space2+1); // inserts middle initial in front of middle name middle.erase (1, -1); // deletes full middle name, leaving only middle initial myString = first + ' ' + middle + ' ' + last; // return 0; }

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  • Finding the Largest and Smallest Integers In A Set- Basic

    - by Ka112324
    I'm kind of on the right track, however my output is not quite right. The program asks for the number of integers you have and then it asks for those numbers. For an example is says please enter the number of integers, you can put 3. And then you enter 3 numbers. I can't use arrays because I am a beginner student and we have not learned those yet. Using count is the only way that allows me to input integers. What do I need to add to my program? Again I am a general computer science student so I can't use anything advanced. I used include iostream, namespace int main and all that you just cant see it int data; int num; int count=0; int max=0; do { cout<<"Enter the number of intergers"<<endl; cin>>num; while (count<num) { cout<<"Please enter a number"<<endl; cin>>data; count++; if (data<min) { min=data; } if (data>max) { max=data; } } cout<<"Smallest integer:"<<min<<endl; cout<<"Largest integer:"<<max<<endl; cout<<"Would you like to continue?"<<endl; cin>>ans; } while ((ans=='y')||(ans=='Y')); return 0; }

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  • How does object of sub-class record information about its super-class the in a Virtual Inheritance

    - 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): 32 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(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; return 0; } Thanks in advance. Kind regards.

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  • About calling an subclass' overriding method when casted to its superclass

    - by Omega
    #include <iostream> class Vehicle { public: void greet() { std::cout << "Hello, I'm a vehicle"; } }; class Car : public Vehicle { public: void greet() { std::cout << "Hello, I'm a car"; } }; class Bike : public Vehicle { public: void greet() { std::cout << "Hello, I'm a bike"; } }; void receiveVehicle(Vehicle vehicle) { vehicle.greet(); } int main() { receiveVehicle(Car()); return 0; } As you can see, I'm trying to send a parameter of type Vehicle to a function, which calls greet(). Car and Bike are subclasses of Vehicle. They overwrite greet(). However, I'm getting "Hello, I'm a vehicle". I suppose that this is because receiveVehicle receives a parameter of type Vehicle instead of a specific subclass like Car or Bike. But that's what I want: I want this function to work with any subclass of Vehicle. Why am I not getting the expected output?

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  • C++ MACRO that will execute a block of code and a certain command after that block.

    - by Poni
    void main() { int xyz = 123; // original value { // code block starts xyz++; if(xyz < 1000) xyz = 1; } // code block ends int original_value = xyz; // should be 123 } void main() { int xyz = 123; // original value MACRO_NAME(xyz = 123) // the macro takes the code code that should be executed at the end of the block. { // code block starts xyz++; if(xyz < 1000) xyz = 1; } // code block ends << how to make the macro execute the "xyz = 123" statement? int original_value = xyz; // should be 123 } Only the first main() works. I think the comments explain the issue. It doesn't need to be a macro but to me it just sounds like a classical "macro-needed" case. By the way, there's the BOOST_FOREACH macro/library and I think it does the exact same thing I'm trying to achieve but it's too complex for me to find the essence of what I need. From its introductory manual page, an example: #include <string> #include <iostream> #include <boost/foreach.hpp> int main() { std::string hello( "Hello, world!" ); BOOST_FOREACH( char ch, hello ) { std::cout << ch; } return 0; }

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