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  • Is it a good practice to pass struct object as parameter to a function in c++?

    - by tsubasa
    I tried an example live below: typedef struct point { int x; int y; } point; void cp(point p) { cout<<p.x<<endl; cout<<p.y<<endl; } int main() { point p1; p1.x=1; p1.y=2; cp(p1); } The result thats printed out is: 1 2 which is what I expected. My question is: Does parameter p get the full copy of object p1? If so, I wonder if this is a good practice? (I assumed when the struct gets big in size, this will create a lot of copy overhead).

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  • Link List Implementation Help - Visual C++

    - by Greenhouse Gases
    Hi there I'm trying to implement a link list which stores the city name (though you will see this commented out as I need to resolve the issue of not being able to use string and needing to use a primitive data type instead during the declaration), longitude, latitude and of course a pointer to the next node in the chain. I am new to the Visual C++ environment and my brain is somewhat scrambled after coding for several straight hours today so I wondered if anyone could help resolve the 2 errors I am getting (ignore the #include syntax as I had to change them to avoid the browser interpreting html!): 1U08221.obj : error LNK2028: unresolved token (0A000298) "public: __thiscall Locations::Locations(void)" (??0Locations@@$$FQAE@XZ) referenced in function "int __clrcall main(cli::array^)" (?main@@$$HYMHP$01AP$AAVString@System@@@Z) 1U08221.obj : error LNK2019: unresolved external symbol "public: __thiscall Locations::Locations(void)" (??0Locations@@$$FQAE@XZ) referenced in function "int __clrcall main(cli::array^)" (?main@@$$HYMHP$01AP$AAVString@System@@@Z) The code for my header file is here: include string struct locationNode { //char[10] nodeCityName; double nodeLati; double nodeLongi; locationNode* Next; }; class Locations { private: int size; public: Locations(); // constructor for the class locationNode* Head; int Add(locationNode* Item); }; and here is the code for the file containing the main method: // U08221.cpp : main project file. include "stdafx.h" include "Locations.h" include iostream include string using namespace std; int n = 0; int x; string cityNameInput; bool acceptedInput = false; int Locations::Add(locationNode *NewItem) { locationNode *Sample = new locationNode; Sample = NewItem; Sample-Next = Head; Head = Sample; return size++; } void CorrectCase(string name) // Correct upper and lower case letters of input { x = name.size(); int firstLetVal = name[0], letVal; n = 1; // variable for name index from second letter onwards if((name[0] 90) && (name[0] < 123)) // First letter is lower case { firstLetVal = firstLetVal - 32; // Capitalise first letter name[0] = firstLetVal; } while(n <= x - 1) { if((name[n] = 65) && (name[n] <= 90)) { letVal = name[n] + 32; name[n] = letVal; } n++; } cityNameInput = name; } void nameValidation(string name) { n = 0; // start from first letter x = name.size(); while(!acceptedInput) { if((name[n] = 65) && (name[n] <= 122)) // is in the range of letters { while(n <= x - 1) { while((name[n] =91) && (name[n] <=97)) // ERROR!! { cout << "Please enter a valid city name" << endl; cin name; } n++; } } else { cout << "Please enter a valid city name" << endl; cin name; } if(n <= x - 1) { acceptedInput = true; } } cityNameInput = name; } int main(array ^args) { cout << "Enter a city name" << endl; cin cityNameInput; nameValidation(cityNameInput); // check is made up of valid characters CorrectCase(cityNameInput); // corrects name to standard format of capitalised first letter, and lower case subsequent letters cout << cityNameInput; cin cityNameInput; Locations::Locations(); Locations *Parts = new Locations(); locationNode *Part; Part = new locationNode; //Part-nodeCityName = "London"; Part-nodeLati = 87; Part-nodeLongi = 80; Parts-Add(Part); } I am familiar with the concepts but somewhat inexperienced with OOP so am making some silly errors that you can never find when you've stared at something too long. Any help you can offer will be appreciated! Thanks

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  • [C++] std::string manipulation: whitespace, "newline escapes '\'" and comments #

    - by rubenvb
    Kind of looking for affirmation here. I have some hand-written code, which I'm not shy to say I'm proud of, which reads a file, removes leading whitespace, processes newline escapes '\' and removes comments starting with #. It also removes all empty lines (also whitespace-only ones). Any thoughts/recommendations? I could probably replace some std::cout's with std::runtime_errors... but that's not a priority here :) const int RecipeReader::readRecipe() { ifstream is_recipe(s_buffer.c_str()); if (!is_recipe) cout << "unable to open file" << endl; while (getline(is_recipe, s_buffer)) { // whitespace+comment removeLeadingWhitespace(s_buffer); processComment(s_buffer); // newline escapes + append all subsequent lines with '\' processNewlineEscapes(s_buffer, is_recipe); // store the real text line if (!s_buffer.empty()) v_s_recipe.push_back(s_buffer); s_buffer.clear(); } is_recipe.close(); return 0; } void RecipeReader::processNewlineEscapes(string &s_string, ifstream &is_stream) { string s_temp; size_t sz_index = s_string.find_first_of("\\"); while (sz_index <= s_string.length()) { if (getline(is_stream,s_temp)) { removeLeadingWhitespace(s_temp); processComment(s_temp); s_string = s_string.substr(0,sz_index-1) + " " + s_temp; } else cout << "Error: newline escape '\' found at EOF" << endl; sz_index = s_string.find_first_of("\\"); } } void RecipeReader::processComment(string &s_string) { size_t sz_index = s_string.find_first_of("#"); s_string = s_string.substr(0,sz_index); } void RecipeReader::removeLeadingWhitespace(string &s_string) { const size_t sz_length = s_string.size(); size_t sz_index = s_string.find_first_not_of(" \t"); if (sz_index <= sz_length) s_string = s_string.substr(sz_index); else if ((sz_index > sz_length) && (sz_length != 0)) // "empty" lines with only whitespace s_string.clear(); } Some extra info: the first s_buffer passed to the ifstream contains the filename, std::string s_buffer is a class data member, so is std::vector v_s_recipe. Any comment is welcome :)

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  • Sprite not moving when using a function from another class SFML c++

    - by user2892932
    I have a Game.cpp, and I am calling a update function in my Player class. In my player update Function I have it to check for keyboard input, and it seems to work, but whenever I try to call the .move() function, it seems to not work. I get no errors either. I am new to sfml, and decent with c++. Help is appreciated! #include "Player.h" Player::Player(void): vel(0), maxvel(100) { Load("Assets/sss.png",true); } void Player::Update(sf::Sprite& p) { if (sf::Keyboard::isKeyPressed(sf::Keyboard::A)) { moveObject(-3,0, p); } if(sf::Keyboard::isKeyPressed(sf::Keyboard::D)) { moveObject(-3,0, p); } } Player::~Player(void) { } This is the GameObject cpp #include "GameObject.h" #include <iostream> GameObject::GameObject(void) { isLoaded = false; } void GameObject::Load(std::string flname, bool isPlayer) { if(!tex.loadFromFile(flname)) { EXIT_FAILURE; } else { if(isPlayer) { if(!tex.loadFromFile(flname, sf::IntRect(0,0,33,33))) { EXIT_FAILURE; } else { std::cout << "Loading image" << "\n"; filename = flname; spr.setTexture(tex); isLoaded = true; } } else { std::cout << "Loading image" << "\n"; filename = flname; spr.setTexture(tex); isLoaded = true; } } } void GameObject::Draw(sf::RenderWindow & window) { if(isLoaded) { window.draw(spr); window.display(); std::cout << "Sprite drew" << "\n"; } } void GameObject::setPos(float x, float y) { if(isLoaded) { spr.setPosition(x,y); } } sf::Vector2f GameObject::GetObjPos() { return spr.getPosition(); } sf::Sprite& GameObject::getSprite() { return spr; } void GameObject::moveObject(float x, float y, sf::Sprite& sp) { sp.move(x, y); } GameObject::~GameObject(void) { }

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  • C++ enumeration

    - by asli
    Hi,my question is about enumeration,my codes are : #include<iostream> using namespace std; int main() { enum bolumler {programcilik,donanim,muhasebe,motor,buro} bolum; bolum = donanim; cout << bolum << endl; bolum += 2; // bolum=motor cout << bolum; return 0; } The output should be 1 3 but according to these codes the error is: error C2676: binary '+=' : 'enum main::bolumler' does not define this operator or a conversion to a type acceptable to the predefined operator Error executing cl.exe. 111.obj - 1 error(s), 0 warning(s) Can you help me ?The other question is what can I do if I want to see the output like that "muhasebe"?

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  • error in encryption program

    - by Raja
    #include<iostream> #include<math.h> #include<string> using namespace std; int gcd(int n,int m) { if(m<=n && n%m ==0) return m; if(n<m) return gcd(m,n); else return gcd(m,n%m); } int REncryptText(char m) { int p = 11, q = 3; int e = 3; int n = p * q; int phi = (p - 1) * (q - 1); int check1 = gcd(e, p - 1); int check2 = gcd(e, q - 1); int check3 = gcd(e, phi); // // Compute d such that ed = 1 (mod phi) //i.e. compute d = e-1 mod phi = 3-1 mod 20 //i.e. find a value for d such that phi divides (ed-1) //i.e. find d such that 20 divides 3d-1. //Simple testing (d = 1, 2, ...) gives d = 7 // double d = Math.Pow(e, -1) % phi; int d = 7; // public key = (n,e) // (33,3) //private key = (n,d) //(33 ,7) double g = pow(m,e); int ciphertext = g %n; // Now say we want to encrypt the message m = 7, c = me mod n = 73 mod 33 = 343 mod 33 = 13. Hence the ciphertext c = 13. //double decrypt = Math.Pow(ciphertext, d) % n; return ciphertext; } int main() { char plaintext[80],str[80]; cout<<" enter the text you want to encrpt"; cin.get(plaintext,79); int l =strlen(plaintext); for ( int i =0 ; i<l ; i++) { char s = plaintext[i]; str[i]=REncryptText(s); } for ( int i =0 ; i<l ; i++) { cout<<"the encryption of string"<<endl; cout<<str[i]; } return 0; }

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  • Passing array to function with pointer loses array size information!

    - by Narek
    If I write int main() { int a[100] = {1,2,3,4,}; cout<<sizeof(a)/sizeof(a[0])<<endl; return 0; } I get 400! If I write void func(int *a); int main() { int a[100] = {1,2,3,4,}; func(a); return 0; } void func(int *a) { cout<<sizeof(a)/sizeof(a[0])<<endl; } Then I get 400! So why passing array to function with pointer loses array size information?

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  • Turing's Craft exercise stumped me... seems too easy.

    - by Chris
    "Write a for loop that prints the integers 1 through 40, separated by spaces or new lines. You may use only one variable, count which has already been declared as an integer." So I use... for(count = 1; count <= 40; count++) { cout << " " << count; } but they are using stdio.h as the only header and cout is not recognized. It hints that the output format should be (" ",count), but I can't figure out what print function to use. stdio.h can use fprintf or fwrite, but I don't have enough parameters for either function. Any ideas?

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  • c++ polymorphism and other function question

    - by aharont
    i have got this code: class father{ public: virtual void f() { cout<<1;} }; class son:public father{ public: void f() {cout<<2;} }; void test (father x){x.f();} int main(){ son s; test(s); } the question says: the output is '1', what is the rule about polymorphism that the programmer forgot and how can i fix it so the output would be '2'? there is another rule that the programmer forgot when he wrote the father class, and he need to add an empty function to avoid problems from other sons of the father class. what is the rule and what is the missing function? another question write the g function so the next code would run with no crashes int x=11; g(x)=22;

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  • Segmentation fault before return

    - by donalmg
    Hi, Why does the following code seg fault before returning: int main() { char iD[20]; memset (iD, 0, 20); char* prefix; srand (time(NULL) ); int iPrefix = rand()%1000000; sprintf(prefix, "%i", iPrefix); int len = strlen(prefix); char* staticChar = "123456789"; //set prefix into ID memcpy(iD, prefix, len); // append static value memcpy(iD+len, staticChar, 20-len); cout << "END " << endl; return 0; } At the minute, the cout will display, but I get a segmentation fault.

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  • OpenCv not initializing usb camera

    - by brainbarshan
    I am trying to capture video from usb camera using OpenCv. #include <highgui.h> #include <iostream> using namespace std; using namespace cv ; int main() { VideoCapture cap (-1); if(!cap.isOpened()) cout << "Cam initialize failed" ; else cout << "Cam initialized" ; return 0; } It is failing to initialize the camera. cap.isOpened() is returning zero. The same program, with same version of OpenCv and same usb camera, is correctly running in my friend's machine. I am running fedora 16. I did some searching in Google and Stack Overflow. But no useful help. Any idea ?

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  • testing directory S_ISDIR acts inconsistently

    - by coubeatczech
    hi, I'm doing simple tests on all files in directory. But from some reason, sometimes, they behave wrongly? What's bad with my code? using namespace std; int main() { string s = "/home/"; struct dirent * file; DIR * dir = opendir(s.c_str()); while ((file = readdir(dir)) != NULL){ struct stat * file_info = new (struct stat); stat(file-d_name,file_info); if ((file_info-st_mode & S_IFMT) == S_IFDIR) cout << "dir" << endl; else cout << "other" << endl; } closedir(dir); }

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  • How to raise an error, if the parsed number of a C++ stdlib stream is immediatly followed by a non whitespace character?

    - by Micha Wiedenmann
    In the following example, I didn't expect, that 1.2345foo would be parsed. Since I am reading data files, it is probably better to raise an error and notify the user. Is peek() the correct thing to do here? #include <iostream> #include <sstream> int main() { std::stringstream in("1.2345foo"); double x; in >> x; if (in) { std::cout << "good\n"; } else { std::cout << "bad\n"; } } Output good

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  • How is inheritance implemented at the memory level?

    - by cambr
    Suppose I have class A { public: void print(){cout<<"A"; }}; class B: public A { public: void print(){cout<<"B"; }}; class C: public C { }; How is inheritance implemented at the memory level? Does C copy print() code to itself or does it have a pointer to the it that points somewhere in A part of the code? How does the same thing happen when we override the previous definition, for example in B (at the memory level)?

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  • What is wrong with this C++ Code ?

    - by mr.bio
    Hi .. i am a beginner and i have a problem : this code doesnt compile : main.cpp: #include <stdlib.h> #include "readdir.h" #include "mysql.h" #include "readimage.h" int main(int argc, char** argv) { if (argc>1){ readdir(argv[1]); // test(); return (EXIT_SUCCESS); } std::cout << "Bitte Pfad angeben !" << std::endl ; return (EXIT_FAILURE); } readimage.cpp #include <Magick++.h> #include <iostream> #include <vector> using namespace Magick; using namespace std; void readImage(std::vector<string> &filenames) { for (unsigned int i = 0; i < filenames.size(); ++i) { try { Image img("binary/" + filenames.at(i)); for (unsigned int y = 1; y < img.rows(); y++) { for (unsigned int x = 1; x < img.columns(); x++) { ColorRGB rgb(img.pixelColor(x, y)); // cout << "x: " << x << " y: " << y << " : " << rgb.red() << endl; } } cout << "done " << i << endl; } catch (Magick::Exception & error) { cerr << "Caught Magick++ exception: " << error.what() << endl; } } } readimage.h #ifndef _READIMAGE_H #define _READIMAGE_H #include <Magick++.h> #include <iostream> #include <vector> #include <string> using namespace Magick; using namespace std; void readImage(vector<string> &filenames) #endif /* _READIMAGE_H */ If want to compile it with this code : g++ main.cpp Magick++-config --cflags --cppflags --ldflags --libs readimage.cpp i get this error message : main.cpp:5: error: expected initializer before ‘int’ i have no clue , why ? :( Can somebody help me ? :)

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  • C++ cin returns 0 for integer no matter what the user inputs

    - by kevin dappah
    No matter the cin it continues to to output 0 for score. Why is that? I tried returning the "return 0;" but still no go :/ #include "stdafx.h" #include <iostream> using namespace std; // Variables int enemiesKilled; const int KILLS = 150; int score = enemiesKilled * KILLS; int main() { cout << "How many enemies did you kill?" << endl; cin >> enemiesKilled; cout << "Your score: " << score << endl; return 0; }

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  • C++ enumaration

    - by asli
    Hi,my question is about enumaration,my codes are : #include<iostream> using namespace std; int main() { enum bolumler{programcilik,donanim,muhasebe,motor,buro} bolum; bolum = donanim; cout<<bolum<<endl; bolum+=2; /* bolum=motor */ cout<<bolum; return 0; } The output should be 1 3 but according to these codes the error is: error C2676: binary '+=' : 'enum main::bolumler' does not define this operator or a conversion to a type acceptable to the predefined operator Error executing cl.exe. 111.obj - 1 error(s), 0 warning(s) Can you help me ?The other question is what can I do if I want to see the output like that "muhasebe"?

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  • Dynamic Object Not Creating for Privately Inherited Class.

    - by mahesh
    Hi, What is the reason for the following code that does not let me to create object. class base { public: void foo() { cout << "base::foo()"; } }; class derived : private base { public: void foo() { cout << "deived::foo()"; } }; void main() { base *d = new derived(); d->foo(); } It Gives me error : " 'type cast' : conversion from 'derived *' to 'base *' exists, but is inaccessible" Thanks in advance :)

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  • Please see following code and answer

    - by user323422
    template <class T> class _cExplicitInstation { public: void show1(T c) { double d =10.02 ; std::cout<<c; } void show2(T d) { std::cout<<d; } }; template _cExplicitInstation<char>; template void _cExplicitInstation<int>::show1(int c); int main() { _cExplicitInstation<char> abc; _cExplicitInstation<int>().show2(10);// it should show error as i have // explicitly declare for show1() function but its working // can u tell why? }

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  • Constant template parameter class manages to link externally

    - by the_drow
    I have a class foo with an enum template parameter and for some reason it links to two versions of the ctor in the cpp file. enum Enum { bar, baz }; template <Enum version = bar> class foo { public: foo(); }; // CPP File #include "foo.hpp" foo<bar>::foo() { cout << "bar"; } foo<baz>::foo() { cout << "baz"; } I'm using msvc 2008, is this the standard behavior? Are only type template parameters cannot be linked to cpp files?

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  • C++ Template const char array to int

    - by Levi Schuck
    So, I'm wishing to be able to have a static const compile time struct that holds some value based on a string by using templates. I only desire up to four characters. I know that the type of 'abcd' is int, and so is 'ab','abc', and although 'a' is of type char, it works out for a template<int v> struct What I wish to do is take sizes of 2,3,4,5 of some const char, "abcd" and have the same functionality as if they used 'abcd'. Note that I do not mean 1,2,3, or 4 because I expect the null terminator. cout << typeid("abcd").name() << endl; tells me that the type for this hard coded string is char const [5], which includes the null terminator on the end. I understand that I will need to twiddle the values as characters, so they are represented as an integer. I cannot use constexpr since VS10 does not support it (VS11 doesn't either..) So, for example with somewhere this template defined, and later the last line template <int v> struct something { static const int value = v; }; //Eventually in some method cout << typeid(something<'abcd'>::value).name() << endl; works just fine. I've tried template<char v[5]> struct something2 { static const int value = v[0]; } template<char const v[5]> struct something2 { static const int value = v[0]; } template<const char v[5]> struct something2 { static const int value = v[0]; } All of them build individually, though when I throw in my test, cout << typeid(something2<"abcd">::value).name() << endl; I get 'something2' : invalid expression as a template argument for 'v' 'something2' : use of class template requires template argument list Is this not feasible or am I misunderstanding something?

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  • Looking at the C++ new[] cookie. How portable is this code?

    - by carleeto
    I came up with this as a quick solution to a debugging problem - I have the pointer variable and its type, I know it points to an array of objects allocated on the heap, but I don't know how many. So I wrote this function to look at the cookie that stores the number of bytes when memory is allocated on the heap. template< typename T > int num_allocated_items( T *p ) { return *((int*)p-4)/sizeof(T); } //test #include <iostream> int main( int argc, char *argv[] ) { using std::cout; using std::endl; typedef long double testtype; testtype *p = new testtype[ 45 ]; //prints 45 std::cout<<"num allocated = "<<num_allocated_items<testtype>(p)<<std::endl; delete[] p; return 0; } I'd like to know just how portable this code is.

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  • C++ WIN32: Short multitasking example

    - by Con Current
    I searched for examples on how to create a simple multithreaded app that does something similar to this: #include <iostream> using namespace std; int myConcurrentFunction( ) { while( 1 ) { cout << "b" << endl; } } int main( ) { // Start a new thread for myConcurrentFunction while( 1 ) { cout << "a" << endl; } } How can I get the above to output a and b "randomly" by starting a new thread instead of just calling myConcurrentFunction normally? I mean: What is the minimal code for it? Is it really only one function I have to call? What files do I need to include? I use MSVC 2010, Win32

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  • C++ cin problems. not capturing input from user

    - by user69514
    I have the following method which is not capturing anything from the user.If I input New Band for the artist name, it only captures "New" and it lefts out "Band". If I use cin.getline() instead nothing is captured. Any ideas how to fix this? char* artist = new char [256]; char * getArtist() { cout << "Enter Artist of CD: " << endl; cin >> artist; cin.ignore(1000, '\n'); cout << "artist is " << artist << endl; return artist; }

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  • C++ arrays select square number and make new vector

    - by John Smith
    I have to see which of the following from a vector is a square number then make another vector with only the square numbers For example: (4,15,6,25,7,81) the second will be (4,25,81) 4,25,81 because 2x2=4 5x5=25 and 9x9=81 I started like this: { int A[100],n,r,i; cout<<"Number of elements="; cin>>n; for(i=1;i<=n;i++) { cout<<"A["<<i<<"]="; cin>>A[i]; } for(i=1;i<=n;i++) { r=sqrt(A[i]); if(r*r==A[i]) } return 0; } but I am not really sure how to continue

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