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  • delegating into private parts

    - by FredOverflow
    Sometimes, C++'s notion of privacy just baffles me :-) class Foo { struct Bar; Bar* p; public: Bar* operator->() const { return p; } }; struct Foo::Bar { void baz() { std::cout << "inside baz\n"; } }; int main() { Foo::Bar b; // error: 'struct Foo::Bar' is private within this context Foo f; f->baz(); // fine } Since Foo::Bar is private, I cannot declare b in main. Yet I can call methods from Foo::Bar just fine. Why the hell is this allowed? Was that an accident or by design?

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  • Why doesn't the C++ default destructor destroy my objects?

    - by Oszkar
    The C++ specification says the default destructor deletes all non-static members. Nevertheless, I can't manage to achieve that. I have this: class N { public: ~N() { std::cout << "Destroying object of type N"; } }; class M { public: M() { n = new N; } // ~M() { //this should happen by default // delete n; // } private: N* n; }; Then this should print the given message, but it doesn't: M* m = new M(); delete m; //this should invoke the default destructor

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  • How to cin Space in c++?

    - by Narek
    Say we have a code: int main() { char a[10]; for(int i = 0; i < 10; i++) { cin>>a[i]; if(a[i] = ' ') cout<<"It is a space!!!"<<<endl; } return 0; } How to cin a Space symbol from command line? If you write space, program ignores! :(

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  • Referencing invalid memory locations with C++ Iterators

    - by themoondothshine
    I am a big fan of GCC, but recently I noticed a vague anomaly. Using __gnu_cxx::__normal_iterator (ie, the most common iterator type used in libstdc++, the C++ STL) it is possible to refer to an arbitrary memory location and even change its value without causing an exception! Is this expected behavior? If so, isn't a security loophole? Here's an example: #include <iostream> using namespace std; int main() { basic_string<char> str("Hello world!"); basic_string<char>::iterator iter = str.end(); iter += str.capacity() + 99999; *iter = 'x'; cout << "Value: " << *iter << endl; }

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  • Normal C++ code in Qt doesnt build and run

    - by Nick
    Hello. I am using Qt under linux, if it matters. I ran successfully under Geany (a simple c++ compiler) the following: //my first program in C++ Hello World! include using namespace std; int main () {cout << "Hello World!"; return 0;} I opened Qt source file and copied the exact same code and i can't build or run. Thank you for your responses to this simple problem.

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  • Strange iterator's behaviour;

    - by A-ha
    #include "stdafx.h" int _tmain(int argc, _TCHAR* argv[]) { string s = "Haven't got an idea why."; auto beg = s.begin(); auto end = s.end(); while (beg < end) { cout << *beg << '\n'; if (*beg == 'a') {//whithout if construct it works perfectly beg = s.erase(beg); } ++beg; } return 0; } Why if I erase one or more chars from this string this code breaks? I suppose it has something to do with returned iterator after erase operation being created at higher address than end iterator but I'm not sure and it surely isn't right behaviour. Or is it?

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  • Getting input in system() function (Mac)

    - by Alex
    #include <iostream> using namespace std; int main() { short int enterVal; cout << "enter a number to say: " << endl; cin >> enterVal; system("say "%d"") << enterVal; return 0; } Is what I am currently trying. I want the user to enter a number and the system() function says it basically. The code above has an error which says " 'd' was not declared in this scope ". Thanks in advance.

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  • WIN32 visual c++

    - by mrbuxley
    I would like to write a simple program in c++. After the program is done i would like to get my answers in form of a graph or picture that would give some certain information if i click on a certain area. i have only written console apllications in c++ before and don't really have a clue where to start with the graphic part of it all. Can I write the first part of the program in console mode and some how run it under the WIN32 later? for ex what will happen to the cout<<"foo"; commands? Is there a simpler approach to do some very basic graphic programming.

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  • Segmentation fault C++ in recursive function

    - by user69514
    Why do I get a segmentation fault in my recursive function. It happens every time i call it when a value greater than 4 as a parameter #include <iostream> #include <limits> using namespace std; int printSeries(int n){ if(n==1){ return 1; } else if( n==2){ return 2; } else if( n==3){ return 3; } else if( n==4){ return printSeries(1) + printSeries(2) + printSeries(3); } else{ return printSeries(n-3) + printSeries((n-2) + printSeries(n-1)); } } int main(){ //double infinity = numeric_limits<double>::max(); for(int i=1; i<=10; i++){ cout << printSeries(i) << endl; } return 0; }

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  • Declare variables that depend on unknown type in template functions.

    - by rem
    Suppose I'm writing a template function foo that has type parameter T. It gets an object of type T that must have method bar(). And inside foo I want to create a vector of objects of type returned by bar. In GNU C++ I can write something like that: template<typename T> void foo(T x) { std::vector<__typeof(x.bar())> v; v.push_back(x.bar()); v.push_back(x.bar()); v.push_back(x.bar()); std::cout << v.size() << std::endl; } How to do the same thing in Microsoft Visual C++? Is there some way to write this code that works in both GNU C++ and Visual C++?

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  • C++ pointer, Beginner Question...

    - by BobAlmond
    Hi there, just want to ask a beginner question... here, I made some code, for understanding the concept/basic of pointer: int a=1; int *b=&a; int **c = &b; int ***d = &c; cout << &*(&*d) << endl; can someone explain to me, why the &*(&d) return address of "c" instead of address of "b"? I've also tried code like &(&(&(&*(&*d)))), but it keep return address of "c" Thanks a lot :)

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  • What key concepts and nuances in C++ you know?

    - by Narek
    What kind of key points and concepts should a person know from C++ (and from programming in general) to be considered that he/she possesses C++ (and programming, in general) skills good. e.g. //Even if sizeof(T) may not be equal to 1, this code steps over array elements T v[]; for(T *p = v ; *p != 0 ; p++) cout<<*p<<endl; P.S. I hope by exchanging this info we will help each other to know C++ and programing thechnics better by doing explicit our notion that we got from practice.

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  • Why I have to redeclare a virtual function while overriding [C++]

    - by Neeraj
    #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

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  • C++ Char without Limit

    - by Lienau
    I'm pretty well versed in C#, but I decided it would be a good idea to learn C++ as well. The only thing I can't figure out is chars. I know you can use the string lib but I also want to figure out chars. I know you can set a char with a limit like this: #include <iostream> using namespace std; int main() { char c[128] = "limited to 128"; cout << c << endl; system("pause"); return 0; } But how would I make a char without a limit? I've seen chars with * but I though that was for pointers. Any help is greatly appreciated.

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  • doubt in - Function Objects - c++

    - by Eternal Learner
    I have a class class fobj{ public: fobj(int i):id(i) {} void operator()() { std::cout<<"Prints"<<std::endl; } private: int id; }; template<typename T> void func(T type) { type(); } My Doubt is if I invoke func like Method 1: func(fobj(1); the message I wanted to print is printed. I was always thinking I needed to do something like Method 2: fobj Iobj(1); // create an instance of the fobj class func(Iobj); //call func by passing Iobj(which is a function object) How does Method 1 work? I mean what exactly happens? and how is a call made to the operator() in class fobj ?

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  • Misunderstanding function pointer - passing it as an argument

    - by Stef
    I want to pass a member function of class A to class B via a function pointer as argument. Please advise whether this road is leading somewhere and help me fill the pothole. #include <iostream> using namespace std; class A{ public: int dosomeA(int x){ cout<< "doing some A to "<<x <<endl; return(0); } }; class B{ public: B(int (*ptr)(int)){ptr(0);}; }; int main() { A a; int (*APtr)(int)=&A::dosomeA; B b(APtr); return 0; } This brilliant piece of code leaves me with the compiler error: cannot convert int (A::*)(int)' toint (*)(int)' in initialization Firstly I want it to compile. Secondly I don't want dosomeA to be STATIC.

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  • C++ how to store integer into a binary file??

    - by blaxc
    i gt a struct with 2 integer, i want to store them in a binary file and read it again... here is my code... struct pw { int a; int b; }; void main(){ pw* p = new pw(); pw* q = new pw(); std::ofstream fout(ADMIN_FILE, ios_base::out | ios_base::binary | ios_base::trunc); std::ifstream fin(ADMIN_FILE, ios_base::in | ios_base::binary); p->a=123; p->b=321; fout.write((const char*)p, sizeof(pw)); fin.write((char*)q, sizeof(pw)); fin.close(); cout<< q->a << endl;} my output is 0. anyone can tell me what is the problem?

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  • what is the reason i am getting out put is 111?

    - by kam
    Hi, #include "stdafx.h" #include<iostream.h> template<class T> class Sample { public: Sample(); static int i; }; template<class T> int Sample<T>::i = 0; template<class T> Sample<T>::Sample() { i++; cout<<i; } void main() { Sample<int>s1; Sample<float>s2; Sample<char>s3; } output: 111 what is the reason i am getting out put is 111?

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  • c++ manipulator question

    - by robert
    i have a class: template<class T> class matrix { private: int COLS,ROWS; public: inline matrix(int r,int c){ this->COLS=r; this->ROWS=c; } template<class T2> friend ostream& info(ostream& os); }; i tried in so many ways to implement the info class.but none is succeed. i want to use it in main function Matrix<int> M(10,20); cout<<info<<M; i want to out put the Matrix class's cols, and rows information. i have tried so many time in implementing the friend class info, but failed. any one can tell me how can do it?

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  • Can nohup change the result of a C++ code?

    - by Biga
    I am having this very weird behaviour with a C++ code: It gives me different results when running with and without 'nohup' (reproducible in cygwin and linux). I mean, if I get the same executable and run it like './run' or run it like 'nohup ./run out.log', I get different results! I use std::cout to output to screen, all lines ending with endl; I use ifstream for the input file; I use ofstream for output, all lines ending with endl. I am using g++ 4. Any idea what is going on?

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  • In C++, I want to implement a ring iterator for a deque that contains a personally defined class.

    - by George
    I have a function of a "Table" class that should add a player to the table. I decided that if the seat is taken, the function should try and go through all the seats and add the player to the next available seat. How do I implement this in my addPlayer function? int Table::addPlayer(Player player, int position) { deque<Player>::iterator it; if(playerList[position] != "(empty seat)") { //What goes here? } playerList.put(player,it); cout >> "Player " >> player.toString >> " sits at position " >> position >> endl; }

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  • How to split the definition of template friend funtion within template class?

    - by ~joke
    The following example compiles fine but I can't figure out how to separate declaration and definition of operator<<() is this particular case. Every time I try to split the definition friend is causing trouble and gcc complains the operator<<() definition must take exactly one argument. #include <iostream> template <typename T> class Test { public: Test(const T& value) : value_(value) {} template <typename STREAM> friend STREAM& operator<<(STREAM& os, const Test<T>& rhs) { os << rhs.value_; return os; } private: T value_; }; int main() { std::cout << Test<int>(5) << std::endl; }

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  • Why the streams in C++?

    - by oh boy
    As you all know there are libraries using streams such as iostream and fstream. My question is: Why streams? Why didn't they stick with functions similar to print, fgets and so on (for example)? They require their own operators << and >> but all they do could be implemented in simple functions like above, also the function printf("Hello World!"); is a lot more readable and logical to me than cout << "Hello World"; I also think that all of those string abstractions in C++ all compile down to (less efficient) standard function calls in binary.

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