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• not working function with no errors

  - by aya

  hello.. I've implemented a function to display an avl tree after inserting nodes into it like this template void AVLtree::display() const { display(Proot); } template void AVLtree::display(Node * ptr) const { if(ptr==0) return ; cout<value<<" "; display(ptr-Pleft); display(ptr-Pright); } after compiling,there were no errors ,the program worked but nothing were printed on the screen help me please....!! thanks

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• I serialized a C++ object, how to allocate memory for it without knowing what type it is?

  - by Neo_b

  Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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• variadic constructors

  - by FredOverflow

  Are variadic constructors supposed to hide the implicitly generated ones, i.e. the default constructor and the copy constructor? struct Foo { template<typename... Args> Foo(Args&&... x) { std::cout << "inside the variadic constructor\n"; } }; int main() { Foo a; Foo b(a); } Somehow I was expecting this to print nothing after reading this answer, but it prints inside the variadic constructor twice on g++ 4.5.0 :( Is this behavior correct?

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• Using Boost statechart, how can I transition to a state unconditionally?

  - by nickb

  I have a state A that I would like to transition to its next state B unconditionally, once the constructor of A has completed. Is this possible? I tried posting an event from the constructor, which does not work, even though it compiles. Thanks. Edit: Here is what I've tried so far: struct A : sc::simple_state< A, Active > { public: typedef sc::custom_reaction< EventDoneA > reactions; A() { std::cout << "Inside of A()" << std::endl; post_event( EventDoneA() ); } sc::result react( const EventDoneA & ) { return transit< B >(); } }; This yields the following runtime assertion failure: Assertion failed: get_pointer( pContext_ ) != 0, file /includ e/boost/statechart/simple_state.hpp, line 459

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• [c++] does a const reference prolong the life of a temporary or not?

  - by Kyle

  Why is the output to this #include <string> #include <iostream> using namespace std; class Sandbox { public: Sandbox(const string& n) : member(n) {} const string& member; }; int main() { Sandbox sandbox(string("four")); cout << sandbox.member << endl; return 0; } this The answer is: and not The answer is: four ?

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• C++ inheritance question

  - by user233973

  Hi guys, I have a C++ inheritance related question. I have a set of classes like this (I have not given the complete class structure coz I am lazy :) ). I want to access chiComponent class public methods using com pointer. How should I go about it? Note that I am having to change the object which "com" is pointing to in a lot of places. So I do not think I can have another chiComponent *ccom = <some_cast> com; ccom.chiComponentMethod() How should I go about it? class Component{ }; class chiComponent : public Component { public: void chiComponentMethod() { cout << "Hi! Chi component function called!!"; } } class parent { protected: Component *com; }; class child : public parent{ public: child() { com = new chiComponent(); } } Regards Arun

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• Nested for_each with lambda not possible?

  - by Ela782

  The following code does not compile in VS2012, it gives error C2064: term does not evaluate to a function taking 1 arguments on the line of the second for_each (line 4 below). vector<string> v1; for_each(begin(v1), end(v1), [](string s1) { vector<string> v2; for_each(begin(v2), end(v2), [](string s2) { cout << "..."; }); }); I found some related stuff like http://connect.microsoft.com/VisualStudio/feedback/details/560907/capturing-variables-in-nested-lambdas which shows a bug (they are doing something different) but on the other hand that shows that what I print above should be possible. What's wrong with the above code?

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• Pointer to struct, containing pointer to an object, for which I want to call a function

  - by user1795609

  So I've created an ADT which is a singly linked list made up of nodes. These Nodes each have a pointer to an object in them called data. Class Structure { struct Node { Object *data; Node *next; }; }; Node *head; I am trying to call a function in the object, like this: head = new Node; head -> data = new Object(); head -> next = NULL; cout << head -> data.print(); I keep getting the following error at compile. error: request for member 'print' in 'head-Structure::Node::data', which is of non-class type 'Object'*

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• Measuring execution time of a call to system() in C++

  - by jm1234567890

  I have found some code on measuring execution time here http://www.dreamincode.net/forums/index.php?showtopic=24685 However, it does not seem to work for calls to system(). I imagine this is because the execution jumps out of the current process. clock_t begin=clock(); system(something); clock_t end=clock(); cout<<"Execution time: "<<diffclock(end,begin)<<" s."<<endl; Then double diffclock(clock_t clock1,clock_t clock2) { double diffticks=clock1-clock2; double diffms=(diffticks)/(CLOCKS_PER_SEC); return diffms; } However this always returns 0 seconds... Is there another method that will work? Also, this is in Linux. Thanks!

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• how do I check if a c++ string is an int?

  - by user342231

  when I use getline, I would input a bunch of strings or numbers, but I only want the while loop to output the "word" if it is not a number. so is there any way to check if "word" is a number or not, I know I could use atoi() for c-strings but how about for strings of the string class int main () { stringstream ss (stringstream::in | stringstream::out); string word; string str; getline(cin,str); ss<<str; while(ss>>word) { //if( ) cout<<word<<endl; } }

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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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• How to retrieve all keys (or values) from a std::map?

  - by Owen

  This is one of the possible ways I come out: struct RetrieveKey { template <typename T> typename T::first_type operator()(T keyValuePair) const { return keyValuePair.first; } }; map<int, int> m; vector<int> keys; // Retrieve all keys transform(m.begin(), m.end(), back_inserter(keys), RetrieveKey()); // Dump all keys copy(keys.begin(), keys.end(), ostream_iterator<int>(cout, "\n")); Of course, we can also retrieve all values from the map by defining another functor RetrieveValues. Is there any other way to achieve this easily? (I'm always wondering why std::map does not include a member function for us to do so.)

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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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• 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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• 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++ 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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• How do I find the speed of an in-progress file upload in cURL?

  - by cinek1lol

  I'd like to know how to check out the speed of a file being uploaded in real time using the cURL library in C++. This is what I have written: void progress_func(void* ptr, double TotalToDownload, double NowDownloaded, double TotalToUpload,double NowUploaded) { cout<<NowUploaded<<endl; } //... int main() { //... curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_func); } But the manual says that it shows average speed, but even this doesn't seem to work with me, because too mach fast is end. How to good write or A well-calculated?

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• XCode 5 says I got a duplicate, which I don't

  - by GoodMove

  The point is every time I try to run a C++ code in XCode 5 (the file s "File.cpp") xcode returns this: duplicate symbol _main ld: 1 duplicate symbol for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation) And it only returns the error, when I got the following function whatever it contains: int main() { } I checked the folder, which XCode points to (where it says the duplicates are placed), but didn't find anything though. What am I supposed to do??? #include "File.h" using namespace std; void func (void){ cout << "Hello World!" << endl; }

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• Reversing a for loop... want to print numbers in reverse

  - by user69514

  How would I change this loop to print prime number in reverse... starting from the biggest one first int main(){ bool prime; for( int i=3; i<=10000; i++){ prime = true; for(int n=2; n<=i-1; n++){ if( i%n == 0){ prime = false; } } if(prime){ cout << i << " "; } } return 0; }

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• Unit testing a functions whose purposes is side effects

  - by David

  How would you unit test do_int_to_string_conversion? #include <string> #include <iostream> void do_int_to_string_conversion(int i, std::string& s) { switch(i) { case 1: s="1"; break; case 2: s="2"; break; default: s ="Nix"; } std::cout << s << "\n"; } int main(int argc, char** argv){ std::string little_s; do_int_to_string_conversion(1, little_s); do_int_to_string_conversion(2, little_s); do_int_to_string_conversion(3, little_s); }

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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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• How To Parse String File Txt Into Array With C++

  - by Ibnu Syuhada

  I am trying to write a C++ program, but I am not familiar with C++. I have a .txt file, which contains values as follows: 0 0.0146484 0.0292969 0.0439453 0.0585938 0.0732422 0.0878906 What I have done in my C++ code is as follows: #include <iostream> #include <fstream> using namespace std; int main() { string line; ifstream myReadFile; myReadFile.open("Qi.txt"); if(myReadFile.is_open()) { while(myReadFile.good()) { getline(myReadFile,line); cout << line << endl; } myReadFile.close(); } return 0; } I would like to make the output of the program an array, i.e. line[0] = 0 line[1] = 0.0146484 line[2] = 0.0292969 line[3] = 0.0439453 line[4] = 0.0585938 line[5] = 0.0732422 line[6] = 0.0878906

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• When convert a void pointer to a specific type pointer, which casting symbol is better, static_cast or reinterpret_cast?

  - by BugCreater

  A beginner question with poor English: Here I got a void* param and want to cast(or change) it to a specific type. But I don't know which "casting symbol" to use. Either**static_cast** and reinterpret_cast works. I want to know which one is better? which one does the Standard C++ recommend? typedef struct { int a; }A, *PA; int foo(void* a) // the real type of a is A* { A* pA = static_cast<A*>(a); // or A* pA = reinterpret_cast<A*>(a);? cout<<pA->a<<endl; return 0; } Here I use A* pA = static_cast(a); or A* pA = reinterpret_cast(a); is more proper?

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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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• 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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