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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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  • Getting a unix timestamp as a string in C++

    - by wyatt
    I'm using the function time() in order to get a timestamp in C++, but, after doing so, I need to convert it to a string. I can't use ctime, as I need the timestamp itself (in its 10 character format). Trouble is, I have no idea what form a time_t variable takes, so I don't know what I'm converting it from. cout handles it, so it must be a string of some description, but I have no idea what. If anyone could help me with this it'd be much appreciated, I'm completely stumped. Alternately, can you provide the output of ctime to a MySQL datetime field and have it interpreted correctly? I'd still appreciate an answer to the first part of my question for understanding's sake, but this would solve my problem.

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  • C++ Detecting ENTER key pressed by user

    - by user69514
    I have a loop where I ask the user to enter a name. I need to stop when the user presses the ENTER key..... or when 20 names have been entered. However my method doesn't stop when the user presses the ENTER key //loop until ENTER key is entered or 20 elements have been added bool stop = false; int ind = 0; while( !stop || ind >= 20 ){ cout << "Enter name #" << (ind+1) << ":"; string temp; getline(cin, temp); int enterKey = atoi(temp.c_str()); if(enterKey == '\n'){ stop = true; } else{ names[ind] = temp; } ind++; }

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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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  • array, I/O file and standard deviation (c++)

    - by JohnWong
    double s_deviation(double data[],int cnt, double mean) { int i; double sum= 0; double sdeviation; double x; //x = mean(billy,a_size); for(i=0; i<cnt; i++) { sum += ((data[i]) - (mean)); } sdeviation = sqrt(sum/((double)cnt)); return sdeviation; } When I cout the result from this function, it gave me NaN. I tested the value of (mean) and data[i] using return data[i] and return mean they are valid. when i replaced mean with an actual number, the operation returned a finite number. but with mean as a variable, it produced NaH. I can't see anything wrong with my code at the moment. Again, I am sure mean, data are getting the right number based on those tests. Thank you

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  • How do I output an individual character when using char *[] = "something"

    - by Matt
    I've been playing with pointers to better understand them and I came across something I think I should be able to do, but can't sort out how. The code below works fine - I can output "a", "dog", "socks", and "pants" - but what if I wanted to just output the 'o' from "socks"? How would I do that? char *mars[4] = { "a", "dog", "sock", "pants" }; for ( int counter = 0; counter < 4; counter++ ) { cout << mars[ counter ]; } Please forgive me if the question is answered somewhere - there are 30+ pages of C++ pointer related question, and I spent about 90 minutes looking through them, as well as reading various (very informative) articles, before deciding to ask.

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  • C++ - defining static const integer members in class definition

    - by HighCommander4
    My understanding is that C++ allows static const members to be defined inside a class so long as it's an integer type. Why, then, does the following code give me a linker error? #include <algorithm> #include <iostream> class test { public: static const int N = 10; }; int main() { std::cout << test::N << "\n"; std::min(9, test::N); } The error I get is: test.cpp:(.text+0x130): undefined reference to `test::N' collect2: ld returned 1 exit status Interestingly, if I comment out the call to std::min, the code compiles and links just fine (even though test::N is also referenced on the previous line). Any idea as to what's going on? My compiler is gcc 4.4 on Linux.

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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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  • 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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  • 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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  • C++ Interpreter: How to emit error messages?

    - by Rawr
    I want to emit dynamic error messages like all interpreters do nowadays, for example: Name error: Undefined variable would be constant, however what I want to reach is: Name error: Undefined variable 'X', in line 1 Okay. The line number was really no problem: Every error message must have a line number, so I added it to the error emitter function: Error( ErrType type, string msg, int line ); So where is my problem? How do I get the 'X' into Undefined variable *? I can't use sprintf as it doesn't support strings yet I use them everywhere I can't simply use cout and connect everything as I want error messages to be supressable I'd like to get everything into one function like above, Error() How do I put together dynamic error messages? For example: Error( Name, sprintf("Undefined variable %s", myVariableName ), lineNum ); (But myVariableName is a string and sprintf will mess things up)

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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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  • 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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  • MPI Barrier C++

    - by aryan
    Dear all, I want to use MPI (MPICH2) on windows. I write this command: MPI_Barrier(MPI_COMM_WORLD); And I expect it blocks all Processors until all group members have called it. But it is not happen. I add a schematic of my code: int a; if(myrank == RootProc) a = 4; MPI_Barrier(MPI_COMM_WORLD); cout << "My Rank = " << myrank << "\ta = " << a << endl; (With 2 processor:) Root processor (0) acts correctly, but processor with rank 1 doesn't know the a variable, so it display -858993460 instead of 4. Can any one help me? Regards

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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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  • 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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  • Strange error that I've never encounter in c++ before, anyone know what it means?

    - by Silmaril89
    Hi, I won't post any code, because there is too much that could be relevant. But When I run my program it prints Internal Bad Op Name! : Success Anybody even know what that means? I'm using g++ to compile my code and nowhere in my code do I cout anything even remotely close to something like that. I don't know where it's coming from. Also, any suggestions as to figure out where in the code it's coming from, maybe using gdb somehow to do that? Thanks!

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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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  • 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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  • Problem with basic program using Boost Threads in c++

    - by Eternal Learner
    I have a simple program which creates and executes as thread using boost threads in c++. #include<boost/thread/thread.hpp> #include<iostream> void hello() { std::cout<<"Hello, i am a thread"<<std::endl; } int main() { boost::thread th1(&hello); th1.join(); } The compiler throws an error against the th1.join() line. It says " Multiple markers at this line - undefined reference to `boost::thread::join()' - undefined reference to `boost::thread::~thread()' "

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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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  • How to declare a variable that spans multiple lines

    - by Chris Wilson
    I'm attempting to initialise a string variable in C++, and the value is so long that it's going to exceed the 80 character per line limit I'm working to, so I'd like to split it to the next line, but I'm not sure how to do that. I know that when splitting the contents of a stream across multiple lines, the syntax goes like cout << "This is a string" << "This is another string"; Is there an equivalent for variable assignment, or do I have to declare multiple variables and concatenate them? Edit: I misspoke when I wrote the initial question. When I say 'next line', I'm just meaning the next line of the script. When it is printed upon execution, I would like it to be on the same line.

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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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