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• const member functions can call const member functions only?

  - by Abhi

  Hi all. Do const member functions call only const member functions? class Transmitter{ const static string msg; mutable int size; public: void xmit() const{ size = compute(); cout<<msg; } private: int compute() const{return 5;} }; string const Transmitter::msg = "beep"; int main(){ Transmitter t; t.xmit(); return EXIT_SUCCESS; } If i dont make compute() a const, then the compiler complains. Is it because since a const member function is not allowed to modify members, it wont allow any calls to non-consts since it would mean that the const member function would be 'indirectly' modifying the data members?

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• Modify input stream data on the fly

  - by Frizi

  I would like to implement a std::stream modifier/parser, that is doing data manipulation on the fly. Is it possible to create it in form of stream manipulator? For example, i want to strip all the line comments (from any // to the end of line) out of the stdin and pass it to stdout. string str; istream strippingCin = cin >> stripcomments; while(strippingCin.good()) { strippingCin >> str; cout << str; } There may be also a large file input instead of cin, so i don't want to load full stream data into memory at once. Is it possible without writing my own stream class? Maybe is there another route i should take instead?

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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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• How to call a function from a shared library?

  - by Frank

  What is the easiest and safest way to call a function from a shared library / dll? I am mostly interested in doing this on linux, but it would be better if there were a platform-independent way. Could someone provide example code to show how to make the following work, where the user has compiled his own version of foo into a shared library? // function prototype, implementation loaded at runtime: std::string foo(const std::string); int main(int argc, char** argv) { LoadLibrary(argv[1]); // loads library implementing foo std::cout << "Result: " << foo("test"); return 0; } BTW, I know how to compile the shared lib (foo.so), I just need to know an easy way to load it at runtime.

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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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• 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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• 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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• 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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• 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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• C++: Declare a global class and access it from other classes?

  - by Regof

  I have a class which should be declared globally from main() and accessed from other declared classes in the program, how do I do that? class A{ int i; int value(){ return i;} }; class B{ global A a; //or extern?? int calc(){ return a.value()+10; } } main(){ global A a; B b; cout<<b.calc(); }

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• Shuffle array variables in a pre-specified order, without using extra memory of "size of input array"

  - by Eternal Learner

  Input : A[4] = {0,4,-1,1000} - Actual Array P[4] = {1,0,3,2} - Order to be reshuffled Output: A[4] = {4,0,1000,-1} Condition : Don't use an additional array as memory. Can use an extra variable or two. Problem : I have the below program in C++, but this fails for certain inputs of array P. #include<iostream> using namespace std; void swap(int *a_r,int *r) { int temp = *r; *r = *a_r; *a_r = temp; } int main() { int A[4] = {0,4,-1,1000}; int P[4] = {3,0,1,2}; int value = A[0] , dest = P[0]; for(int i=0; i<4;i++) { swap(&A[dest],&value); dest = P[dest]; } for(int i=0;i<4;i++) cout<<A[i]<<" "; }

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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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• 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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• trying to sort a simple string in c++

  - by every_answer_gets_a_point

  #include "stdio.h" #include "conio.h" #include <iostream> using namespace std; int main (void) { char my_char[] = "happy birthday"; int i; bool j=false; char my_char_temp[1]; do { for (i=0;i<sizeof(my_char)-2;i++) { j=false; if (my_char[i+1] < my_char[i]) { my_char_temp[0]=my_char[i+1]; my_char[i+1] = my_char[i]; my_char[i] = my_char_temp[0]; j=true; } } }while (j); cout << my_char; } what am i doing wrong? im just trying to sort the letters within the char the output i get is completely wrong

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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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• Programmatically find maximum static array size in C++

  - by GuyGreer

  I am curious whether it is possible to determine the maximum size that an array can have in C++. #include <iostream> using namespace std; #define MAX 2000000 int main() { long array[MAX]; cout << "Message" << endl; return 0; } This compiles just fine, but then segfaults as soon as I run it (even though array isn't actually referenced). I know it's the array size too because if I change it to 1000000 it runs just fine. So, is there some define somewhere or some way of having #define MAX MAX_ALLOWED_ARRAY_SIZE_FOR_MY_MACHINE_DEFINED_SOMEWHERE_FOR_ME? I don't actually need this for anything, this question is for curiosity's sake.

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• Why does this C++ char array seem to be able to hold more than its size?

  - by Phenom

  #include <iostream> using namespace std; typedef struct { char streetName[5]; } RECORD; int main() { RECORD r; cin >> r.streetName; cout << r.streetName << endl; } When I run this program, if I enter in more than 5 characters, the output will show the whole string I entered. It does not truncate at 5 characters. Why is that? How can I get this to work correctly?

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• How does the stream manipulators work?

  - by Narek

  It is well known that the user can define stream manipulators like this: ostream& tab(ostream & output) { return output<< '\t'; } And this can be used in main() like this: cout<<'a'<<tab<<'b'<<'c'<<endl; Please explain me how does this all work? If operator<< assumes as a second parameter a pointer to the function that takes and returns ostream &, then please explain my why it is necessary? What would be wrong if the function does not take and return ostream & but it was void instead of ostream &? Also it is interesting why “dec”, “hex” manipulators take effect until I don’t change between them, but user defined manipulators should be always used in order to take effect for each streaming?

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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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• How to get path to current exe file on Linux?

  - by user1519221

  The code below gives current path to exe file on Linux: #include <iostream> std::string getExePath() { char result[ PATH_MAX ]; ssize_t count = readlink( "/proc/self/exe", result, PATH_MAX ); return std::string( result, (count > 0) ? count : 0 ); } int main() { std::cout << getExePath() << std::endl; return 0; } The problem is that when I run it gives me current path to exe and name of the exe, e.g.: /home/.../Test/main.exe I would like to get only /home/.../Test/ I know that I can parse it, but is there any nicer way to do that?

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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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• 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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• 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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