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• Pure virtual destructor in interface

  - by ALOR

  Hello all. Here is my problem. I'm making C++ dll, which extensively relies on instance object exports. So i return my actual instances as a pointers to interface through some exported factory method. Interfaces i use are purely virtual, to avoid linking problame. So i need a pure virtual destructor too, and i implemented one (with empty body, as i googled it). All compiles perfectly well, except... I can't see, if the actual destructors are called or not - because when i added some std::cout << "hello destructor"; i never get to see it. I have some explicit "delete obj", that's not the problem. Am i missing something? Is there another way to delete my object through interface?

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• Multiple-File Template Implementation

  - by Maxpm

  With normal functions, the declaration and definition are often separated across multiple files like so: // Foo.h namespace Foo { void Bar(); } . // Foo.cpp #include "Foo.h" void Foo::Bar() { cout << "Inside function." << endl; } It is my understanding that this cannot be done with templates. The declaration and definition must not be separate because the appropriate form of the template is created "on-demand" when needed. So, how and where are templates typically defined in a multiple-file project like this? My intuition is that it would be in Foo.cpp because that's where the "meat" of functions normally is, but on the other hand it's the header file that's going to be included.

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• C++: can't static_cast from double* to int*

  - by samoz

  When I try to use a static_cast to cast a double* to an int*, I get the following error: invalid static_cast from type ‘double*’ to type ‘int*’ Here is the code: #include <iostream> int main() { double* p = new double(2); int* r; r=static_cast<int*>(p); std::cout << *r << std::endl; } I understand that there would be problems converting between a double and an int, but why is there a problem converting between a double* and an int*?

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• Why is visual studio not aware that an integer's value is changing? (debugging)

  - by incrediman

  I have a few simple lines of code (below). [bp] indicates a breakpoint. for(int i=0;i<300;i++){} int i=0; cout<<i; [bp] for (i=0;i<200;i++){} When I debug this in visual studio, it tells me that i is equal to 300 on the breakpoint. Annoyingly, 0 is printed to the console. Is there any way to make it realize that two variables in different scopes can actually have the same name? I also want to add some code to the second loop and then debug it - but when I try to do that, i is consistently shown as 300. Very annoying.

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• Void pointer values comparing C++

  - by user2962977

  My actual question is it really possible to compare values contained in two void pointers, when you actually know that these values are the same type? For example int. void compVoids(void *firstVal, void *secondVal){ if (firstVal < secondVal){ cout << "This will not make any sense as this will compare addresses, not values" << endl; } } Actually I need to compare two void pointer values, while outside the function it is known that the type is int. I do not want to use comparison of int inside the function. So this will not work for me as well: if (*(int*)firstVal > *(int*)secondVal) Any suggestions? Thank you very much for help!

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• Does C++ have a static polymorphism implementation of interface that does not use vtable?

  - by gilbertc

  Does C++ have a proper implementation of interface that does not use vtable? for example class BaseInterface{ public: virtual void func() const = 0; } class BaseInterfaceImpl:public BaseInterface{ public: void func(){ std::cout<<"called."<<endl; } } BaseInterface* obj = new BaseInterfaceImpl(); obj->func(); the call to func at the last line goes to vtable to find the func ptr of BaseInterfaceImpl::func, but is there any C++ way to do that directly as the BaseInterfaceImpl is not subclassed from any other class besides the pure interface class BaseInterface? Thanks. Gil.

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• Segfault when calling a method c++

  - by shuttle87

  I am fairly new to c++ and I am a bit stumped by this problem. I am trying to assign a variable from a call to a method in another class but it always segfaults. My code compiles with no warnings and I have checked that all variables are correct in gdb but the function call itself seems to cause a segfault. The code I am using is roughly like the following: class History{ public: bool test_history(); }; bool History::test_history(){ std::cout<<"test"; //this line never gets executed //more code goes in here return true; } class Game{ private: bool some_function(); public: History game_actions_history; bool local_variable; }; bool Game::some_function(){ local_variable = game_actions_history.test_history(); if (local_variable == true){ return true; } else{ return false; } } Any tips or advice is greatly appreciated!

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• Constructor return value

  - by Ivan Gromov

  Could you tell me what is wrong with my class constructor? Code: CVector::CVector (int size_) { if (size_ > 0) { this->size = size_; this->data = new double[size]; for (int i = 0; i < size; i++) { (*this)(i) = i; } } cout << "constructor end" << endl; return; } Usage example: tvector = CVector(6); I get an access violation after "constructor end" output.

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• C++: Binding to a base class

  - by Helltone

  The following code works, but I'm not sure it is correct/portable. #include <iostream> #include <tr1/functional> class base { public: base(int v) : x(v) {} protected: int x; }; class derived : public base { public: bool test() { return (x == 42); } }; int main(int argc, char* argv[]) { base b(42); if(std::tr1::bind((bool (base::*)()) &derived::test, b)()) { std::cout << "ok\n"; } return 0; }

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• C++ Pointers to functions.

  - by Andy Leman

  using namespace std; int addition (int a, int b) { return (a+b); } int subtraction (int a, int b) { return (a-b); } int operation (int x, int y, int (*functocall)(int,int)) { int g; g = (*functocall)(x,y); return(g); } int main() { int m,n; int (*minus)(int,int) = subtraction; m = operation (7,5,addition); n = operation (20,m,minus); cout << n; return 0; } Can anybody explain this line for me int (*minus)(int,int) = subtraction; Thanks a lot!

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• Disallow private constructor invocation in friend function

  - by user2907032

  Is there any way to not allow private construction in friend function, In case we do have private constructor with friend function in our class. Only Static method should be responsible for object creation and other than this compiler should flash error message #include <iostream> #include <memory> using namespace std; class a { public: void see () { cout<<"Motimaa"; } static a& getinstance() { static a instance; return instance; } private: a() {}; friend void access(); }; void access () { a obj; obj.see();//still friend function can access } int main() { a::getinstance().see(); access(); return 1; }

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• Howto read only one line via c++ from a data

  - by Markus Hupfauer

  i tryed to read the first line of a .dat data, but when i tryed to give to text, wich was saved in the .dat data, it print out the whole data, not only one line. the tool is also not looking after breaks or spaces :( Im using the following code: //Vocabel.dat wird eingelesen ifstream f; // Datei-Handle string s; f.open("Vocabeln.dat", ios::in); // Öffne Datei aus Parameter while (!f.eof()) // Solange noch Daten vorliegen { getline(f, s); // Lese eine Zeile cout << s; } f.close(); // Datei wieder schließen getchar(); . So could u help me please ? . Thanks a lot Markus

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• How to read the whole istream correctly?

  - by L.Lawliet

  Here is a simple code to print all characters of a txt file on screen: #include <iostream> #include <fstream> #include <string> using namespace std; int main() { int **i; int j,k; char a; ifstream test("test.txt", ios::binary); while((a=test.get())!=-1)//if I use "while(!test.eof())" here, how to avoid the output of the last character(-1) to std::cout, or any ostream objects? { putchar(a);//also change this to putchar(test.get()); } getchar(); } As I noted in the code, if I use "test.eof()" to judge the end of test.txt, I'll always get an extra blank at the end of the output. How to avoid it?

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• Stack Overflow Accessing Large Vector

  - by cam

  I'm getting a stack overflow on the first iteration of this for loop for (int q = 0; q < SIZEN; q++) { cout<<nList[q]<<" "; } nList is a vector of type int with 376 items. The size of nList depends on a constant defined in the program. The program works for every value up to 376, then after 376 it stops working. Any thoughts?

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• Does C++ have a proper implementation of interface that does not use vtable?

  - by gilbertc

  Does C++ have a proper implementation of interface that does not use vtable? for example class BaseInterface{ public: virtual void func() const = 0; } class BaseInterfaceImpl:public BaseInterface{ public: void func(){ std::cout<<"called."<<endl; } } BaseInterface* obj = new BaseInterfaceImpl(); obj->func(); the call to func at the last line goes to vtable to find the func ptr of BaseInterfaceImpl::func, but is there any C++ way to do that directly as the BaseInterfaceImpl is not subclassed from any other class besides the pure interface class BaseInterface? Thanks. Gil.

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• findNode in binary search tree

  - by Weadadada Awda

  Does this look right? I mean I am trying to implement the delete function. Node* BST::findNode(int tofind) { Node* node = new Node; node = root; while (node != NULL) { if (node->val == tofind) { return node; } else if (tofind < node->val) { node = node->left; } else { node = node->right; } } } Here is the delete, it's not even close to done but, void BST::Delete(int todelete) { // bool found = false; Node* toDelete = new Node(); toDelete=findNode(todelete); if(toDelete->val!=NULL) { cout << toDelete->val << endl; } } This causes a segmentation fault just running that, any ideas?

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• printing double in binary

  - by Happy Mittal

  In Thinking in C++ by Bruce eckel, there is a program given to print a double value in binary.(Chapter 3, page no. 189) int main(int argc, char* argv[]) { if(argc != 2) { cout << "Must provide a number" << endl; exit(1); } double d = atof(argv[1]); unsigned char* cp = reinterpret_cast<unsigned char*>(&d); for(int i = sizeof(double); i > 0 ; i -= 2) { printBinary(cp[i-1]); printBinary(cp[i]); } } Here while printing cp[i] when i=8(assuming double is of 8 bytes), wouldn't it be undefined behaviour? I mean this code doesn't work as it doesn't print cp[0].

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• problem in reading output of dd command using pipe

  - by Ummar

  I am developing an application, in which I want to redirect the output (progress information) of dd command to my C++ program, but it is not actually getting the output, here is the code FILE * progressInfo = popen("gzip -dc backup/backup.img.gz | pv -ptrbe -i 2 -s 2339876653 | dd of=/dev/sdb","r"); if(!progressInfo) { return -1; } char buf[1024]; while(fgets(buff, sizeof(buff),progressInfo)!=NULL) { std::cout << buff << endl; } but the problem is the progress information is not received in buff, and the output is continuously printed on terminal, and above program halts on while(fgets(buff, sizeof(buff),progressInfo)!=NULL), and as soon as the dd operation is completed, the very next line to loop block is executed. if anyone has any idea why the output is not returned to buff, and its continuously retuned on terminal?

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• Using scanf() in C++ programs is faster than using cin ?

  - by zeroDivisible

  Hello, I don't know if this is true, but when I was reading FAQ on one of the problem providing sites, I found something, that poke my attention: Check your input/output methods. In C++, using cin and cout is too slow. Use these, and you will guarantee not being able to solve any problem with a decent amount of input or output. Use printf and scanf instead. Can someone please clarify this? Is really using scanf() in C++ programs faster than using cin something ? If yes, that is it a good practice to use it in C++ programs? I thought that it was C specific, though I am just learning C++...

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• Doesnt the Visual Studio 2008 compiler autocast to double with sqrt in C++?

  - by Chris_45

  Shouldn't the compiler automatically cast to a double in this case at least according to Walter Savitch: #include <iostream> #include <cmath> using namespace std; int main(){ int k; for(k = 1; k <= 10; k++) cout << "The square root of i is: " << sqrt(k) << endl; return 0; }//error C2668: 'sqrt' : ambiguous call to overloaded function //Visual Studio 2008 on Win Vista

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• encryption problem for wlan profile

  - by Jassi

  i am trying to encrypt keyMaterial element from wireless profile. so I want to convert byte array into OLECHAR but it is giving me wrong output not key sea the below code you may know the solution... DATA_BLOB in; DATA_BLOB out; BYTE pin=(BYTE)"FIPL2"; DWORD din=strlen((char*)pin)+1; in.pbData = pin; in.cbData = din; if(CryptProtectData(&in,L"what is it",NULL,NULL,NULL,0,&out)) { BYTE *b=out.pbData; USES_CONVERSION; bstr=SysAllocString(W2BSTR((const WCHAR *)b)); HRCALL(peSubS222->put_text(bstr), ""); SysFreeString(bstr); bstr=NULL; } else { cout<<"NOOOOOOOOOOOOOOOO :("; } what is missing please help me out

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• How do I convert a single char in string to an int

  - by Guest

  Keep in mind, if you choose to answer the question, I am a beginner in the field of programming and may need a bit more explanation than others as to how the solutions work. Thank you for your help. My problem is that I am trying to do computations with parts of a string (consisting only of numbers), but I do not know how to convert an individual char to an int. The string is named "message". for (int place = 0; place < message.size(); place++) { if (secondPlace == 0) { cout << (message[place]) * 100 << endl; } } Thank you.

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• How to write Cyrillic text in C++ console?

  - by VextoR

  For example, if I write: cout << "??????!" << endl; //it's hello in Russian in console it would be something like "-?????!" ok, I know that we can use: setlocale(LC_ALL, "Russian"); but after that not working command line arguments in russian (if I start my program through BAT file): StartProgram.bat chcp 1251 MyProgram.exe -user=???? -password=?????? so, after setlocale program can't read russian arguments properly. This happens because BAT file in CP1251, but console is in CP866 So, there is a question: How to write in C++ console russian text and same time russian command line arguments have to be read properly thanks

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• Question about char input

  - by DomX23

  This is what I'm trying to do... char input[4]; cin >> input; cout << "Input[0]: " << input[0] << "Input[1]: " << input[1] << "Input[2]: " << input[2] << "Input[3] " << input[3]<< "Input[4] " << input[4] <<endl; However, when I enter "P F" I get an out of this: Input[0]:P Input[1]: Input[2]: Input[3] Input[4] Why do I get that weird character instead of F?

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• why this signal handler is called infinitely

  - by lz_prgmr

  I am using Mac OS 10.6.5, g++ 4.2.1. And meet problem with following code: #include <iostream> #include <sys/signal.h> using namespace std; void segfault_handler(int signum) { cout << "segfault caught!!!\n"; } int main() { signal(SIGSEGV, segfault_handler); int* p = 0; *p = 100; return 1; } It seems the segfault_handler is called infinitely and keep on print: segfault caught!!! segfault caught!!! segfault caught!!! ... I am new to Mac development, do you have any idea on what happened?

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