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  • returning reference to a vector from a method and using its public members

    - by memC
    dear experts, I have a vector t_vec that stores references to instances of class Too. The code is shown below. In the main , I have a vector t_vec_2 which has the same memory address as B::t_vec. But when I try to access t_vec_2[0].val1 it gives error val1 not declared. Could you please point out what is wrong? Also, if you know of a better way to return a vector from a method, please let me know! Thanks in advance. class Too { public: Too(); ~Too(){}; int val1; }; Too::Too(){ val1 = 10; }; class B { public: vector<Too*> t_vec; Too* t1; vector<Too*>& get_tvec(); B(){t1 = new Too();}; ~B(){delete t1;}; }; vector<Too*>& B::get_tvec(){ t_vec.push_back(t1); return t_vec; } int main(){ B b; b = B(); vector<Too*>& t_vec_2 = b.get_tvec(); // Getting error std::cout << "\n val1 = " << t_vec_2[0].val1; return 0; }

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  • c++ tables of unions and structures

    - by newbDeveloper
    I was told to write a program, that creates a union and structure, then creates two-element arrays of unions and structures and fills their fields. I have created a union and a structure, but how to fill their fields in arrays ? #include <iostream> #include <stdlib.h> #include <stdio.h> using namespace std; union complex; union complex{ int i1; long double ld1; } u; struct Person { char* name; int age; bool sex; void show(){ printf("name %s, age %2.0d, sex %1d\n", name , age, sex); }; } person; int main(void) { Person *o = new Person[2]; complex *un = new complex[2]; un[0]->i1=i; system("pause"); return 0; } I've tried un[0]-i1=i; but it's not the proper way to do this.

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  • Proper QUuid usage in Qt ? (7-Zip DLL usage problems (QLibrary, QUuid GUID conversion, interfaces))

    - by whipsnap
    Hi, I'm trying to write a program that would use 7-Zip DLL for reading files from inside archive files (7z, zip etc). Here's where I'm so far: #include QtCore/QCoreApplication #include QLibrary #include QUuid #include iostream using namespace std; #include "7z910/CPP/7zip/Archive/IArchive.h" #include "7z910/CPP/7zip/IStream.h" #include "MyCom.h" // {23170F69-40C1-278A-1000-000110070000} QUuid CLSID_CFormat7z(0x23170F69, 0x40C1, 0x278A, 0x10, 0x00, 0x00, 0x01, 0x10, 0x07, 0x00, 0x00); typedef int (*CreateObjectFunc)( const GUID *clsID, const GUID *interfaceID, void **outObject); void readFileInArchive() { QLibrary myLib("7z.dll"); CreateObjectFunc myFunction = (CreateObjectFunc)myLib.resolve("CreateObject"); if (myFunction == 0) { cout outArchive; myFunction(&CLSID_CFormat7z, &IID_IOutArchive, (void **)&outArchive); } int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); readFileInArchive(); return a.exec(); } Trying to build that in Qt Creator will lead to following error: cannot convert 'QUuid*' to 'const GUID*' in argument passing How should QUuid be correctly used in this context? Also, being a C++ and Qt newbie I haven't yet quite grasped templates or interfaces, so overall I'm having trouble getting through these first steps. If someone could give tips or even example code on how for example an image file could be extracted from ZIP file (to be shown in Qt GUI later on*), I would highly appreciate that. My main goal at the moment is to write a program with GUI for selecting archive files containing image files (PNG, JPG etc) and displaying those files one at a time in the GUI. A Qt based CDisplayEx in short.

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  • Ping broadcast on Win XP SP3

    - by PaulH
    I'm trying to ping the broadcast address 255.255.255.255 on WinXP SP3. If I use the command line, I get host error: C:\>ping 255.255.255.255 Ping request could not find host 255.255.255.255. Please check the name and try again. If I try a C++ program using the iphlpapi, IcmpSendEcho() fails and GetLastError returns 11010 IP_REQ_TIMED_OUT. HANDLE h = ::IcmpCreateFile(); IPAddr broadcast = inet_addr( "255.255.255.255" ); BYTE payload[ 32 ] = { 0 }; IP_OPTION_INFORMATION option = { 255, 0, 0, 0, 0 }; // a buffer with room for 32 replies each containing the full payload std::vector< BYTE > replies( 32 * ( sizeof( ICMP_ECHO_REPLY ) + 32 ) ); DWORD res = ::IcmpSendEcho( h, broadcast, payload, sizeof( payload ), &option, &replies[ 0 ], replies.size(), 1000 ); ::IcmpCloseHandle( h ); I can ping the local broadcast 192.168.0.255 with no problem. What do I need to do to ping the global broadcast? Thanks, PaulH

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  • Using stringstream instead of `sscanf` to parse a fixed-format string

    - by John Dibling
    I would like to use the facilities provided by stringstream to extract values from a fixed-format string as a type-safe alternative to sscanf. How can I do this? Consider the following specific use case. I have a std::string in the following fixed format: YYYYMMDDHHMMSSmmm Where: YYYY = 4 digits representing the year MM = 2 digits representing the month ('0' padded to 2 characters) DD = 2 digits representing the day ('0' padded to 2 characters) HH = 2 digits representing the hour ('0' padded to 2 characters) MM = 2 digits representing the minute ('0' padded to 2 characters) SS = 2 digits representing the second ('0' padded to 2 characters) mmm = 3 digits representing the milliseconds ('0' padded to 3 characters) Previously I was doing something along these lines: string s = "20101220110651184"; unsigned year = 0, month = 0, day = 0, hour = 0, minute = 0, second = 0, milli = 0; sscanf(s.c_str(), "%4u%2u%2u%2u%2u%2u%3u", &year, &month, &day, &hour, &minute, &second, &milli ); The width values are magic numbers, and that's ok. I'd like to use streams to extract these values and convert them to unsigneds in the interest of type safety. But when I try this: stringstream ss; ss << "20101220110651184"; ss >> setw(4) >> year; year retains the value 0. It should be 2010. How do I do what I'm trying to do? I can't use Boost or any other 3rd party library, nor can I use C++0x.

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  • Solved: Help with this compile error

    - by Scott
    I just picked up an old project and I'm not sure what the following error could mean. g++ -o BufferedReader.o -c -g -Wall -std=c++0x -I/usr/include/xmms2 -Ijsoncpp/include/json/ -fopenmp -I/usr/include/ImageMagick -I/usr/include/xmms2 -I/usr/include/libvisual-0.4 -D_GNU_SOURCE=1 -D_REENTRANT -I/usr/include/SDL -DQT_CORE_LIB -DQT_GUI_LIB -DQT_SCRIPT_LIB -DQT_SHARED -I/usr/include/QtCore -I/usr/include/QtGui -I/usr/include/QtScript BufferedReader.cpp In file included from BufferedReader.cpp:23: /usr/include/string.h:36:42: error: missing binary operator before token "(" In file included from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/cwchar:47, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/bits/postypes.h:42, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/iosfwd:42, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/ios:39, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/istream:40, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/sstream:39, from BufferedReader.cpp:24: At line 24 of BufferedReader.cpp is #include <string.h>. I've tried it with just <string> but get the same thing. Any clue? Here's the snippet of code from string.h /* Tell the caller that we provide correct C++ prototypes. */ #if defined __cplusplus && __GNUC_PREREQ (4, 4) //line 36 # define __CORRECT_ISO_CPP_STRING_H_PROTO #endif Does that mean __GNUC_PREREQ isn't defined? Edit: Changing -Ijsoncpp/include/json/ to Ijsoncpp/include stopped the errors. I noticed I was including <json/json.h>. I'm about to switch to JsonGlib though, which is the reason I pulled the project up again. So it's all good. :)

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  • Suggestions on error handling of Win32 C++ code: AtlThrow vs. STL exceptions

    - by EmbeddedProg
    In writing Win32 C++ code, I'd appreciate some hints on how to handle errors of Win32 APIs. In particular, in case of a failure of a Win32 function call (e.g. MapViewOfFile), is it better to: use AtlThrowLastWin32 define a Win32Exception class derived from std::exception, with an added HRESULT data member to store the HRESULT corresponding to value returned by GetLastError? In this latter case, I could use the what() method to return a detailed error string (e.g. "MapViewOfFile call failed in MyClass::DoSomething() method."). What are the pros and cons of 1 vs. 2? Is there any other better option that I am missing? As a side note, if I'd like to localize the component I'm developing, how could I localize the exception what() string? I was thinking of building a table mapping the original English string returned by what() into a Unicode localized error string. Could anyone suggest a better approach? Thanks much for your insights and suggestions.

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  • Segmentation fault on instationation of more than 1 object

    - by ECE
    I have a class called "Vertex.hpp" which is as follows: #include <iostream> #include "Edge.hpp" #include <vector> using namespace std; /** A class, instances of which are nodes in an HCTree. */ class Vertex { public: Vertex(char * str){ *name=*str; } vector<Vertex*> adjecency_list; vector<Edge*> edge_weights; char *name; }; #endif When I instantiate an object of type Vector as follows: Vertex *first_read; Vertex *second_read; in.getline(input,256); str=strtok(input," "); first_read->name=str; str=strtok(NULL, " "); second_read->name=str; A segmentation fault occurs when more than 1 object of type Vector is instantiated. Why would this occur if more than 1 object is instantiated, and how can i allow multiple objects to be instantiated?

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  • Can redirection of screen output to file 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 redirecting the screen output to a file (reproducible in cygwin and linux). I mean, if I get the same executable and run it like ./run or run it like ./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? UPDATE: I have hard-coded the input data, so 'ifstream' is not used, and problem persists. UPDATE 2: That's getting interesting. I have probed three variables that are computed initially, and that's what I get when using with and without redirecting the output to file redirected to file: 0 -0.02 0 direct to screen: 0 -0.02 1.04083e-17 So there's a round-off difference in the code variables with and without redirecting the output! Now, why redirecting would interefere with an internal computation of the code? UPDATE 3: If I redirect to /dev/null, I get the sam behaviour as outputing direct to screen, instead of redirecting to file.

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  • The program fails to display `cout` when it is run

    - by Jeff - FL
    Hello, I justed started a C++ course & I wrote, compiled, debugged & ran my first program: // This program calculates how much a little league team spent last year to purchase new baseballs. #include <iostream> using namespace std; int baseballs; int cost; int total; int main() { baseballs, cost, total; // Get the number of baseballs were purchased. cout << "How many baseballs were purchased? "; cin >> baseballs; // Get the cost of baseballs purchased. cout << "What was the cost of each baseball purchased? "; cin >> cost; // Calculate the total. total = baseballs * cost; // Display the total. cout << "The total amount spent $" << total << endl; return 0; } The only probelm that I encountered was that when I ran the program it failed to display the total amount spent (cout). Could someone please explain why? Thanks Jeff H - Sarasota, FL

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  • Creating a C++ DLL and then using it in C#

    - by Major
    Ok I'm trying to make a C++ DLL that I can then call and reference in a c# App. I've already made a simple dll using the numberous guides out there, however when I try to reference it in the C# app I get the error Unable to load DLL 'SDES.dll': The specified module could not be found. The code for the program is as follows (bear with me I'm going to include all the files) //These are the DLL Files. ifndef TestDLL_H define TestDLL_H extern "C" { // Returns a + b __declspec(dllexport) double Add(double a, double b); // Returns a - b __declspec(dllexport) double Subtract(double a, double b); // Returns a * b __declspec(dllexport) double Multiply(double a, double b); // Returns a / b // Throws DivideByZeroException if b is 0 __declspec(dllexport) double Divide(double a, double b); } endif //.cpp include "test.h" include using namespace std; extern double __cdecl Add(double a, double b) { return a + b; } extern double __cdecl Subtract(double a, double b) { return a - b; } extern double __cdecl Multiply(double a, double b) { return a * b; } extern double __cdecl Divide(double a, double b) { if (b == 0) { throw new invalid_argument("b cannot be zero!"); } return a / b; } //C# Program using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Runtime.InteropServices; namespace ConsoleApplication1 { class Program { [DllImport("SDES.dll")] public static extern void SimulateGameDLL(int a, int b); static void Main(string[] args) { SimulateGameDLL(1, 2); //Error here... } } } Anyone have any idea's what I may be missing in my program? Let me know if I missed some code or if you have any questions.

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  • give feedback on this pointer program

    - by JohnWong
    This is relatively simple program. But I want to get some feedback about how I can improve this program (if any), for example, unnecessary statements? #include<iostream> #include<fstream> using namespace std; double Average(double*,int); int main() { ifstream inFile("data2.txt"); const int SIZE = 4; double *array = new double(SIZE); double *temp; temp = array; for (int i = 0; i < SIZE; i++) { inFile >> *array++; } cout << "Average is: " << Average(temp, SIZE) << endl; } double Average(double *pointer, int x) { double sum = 0; for (int i = 0; i < x; i++) { sum += *pointer++; } return (sum/x); } The codes are valid and the program is working fine. But I just want to hear what you guys think, since most of you have more experience than I do (well I am only a freshman ... lol) Thanks.

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  • Why does double dispatch not work in C++?

    - by Bruce
    #include<iostream.h> #include<conio.h> using namespace std; class SpaceShip {}; class GiantSpaceShip : public SpaceShip {}; class Asteroid { public: virtual void CollideWith(SpaceShip *) { cout << "Asteroid hit a SpaceShip" << endl; } virtual void CollideWith(GiantSpaceShip *) { cout << "Asteroid hit a GiantSpaceShip" << endl; } }; class ExplodingAsteroid : public Asteroid { public: virtual void CollideWith(SpaceShip *) { cout << "ExplodingAsteroid hit a SpaceShip" << endl; } virtual void CollideWith(GiantSpaceShip *) { cout << "ExplodingAsteroid hit a GiantSpaceShip" << endl; } }; int main() { SpaceShip * s = new GiantSpaceShip(); Asteroid * a = new ExplodingAsteroid(); a->CollideWith(s); getch(); return 0; } How can I enable double dispatch in C++?

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  • creating a QT gui using a thread in c++?

    - by rashid
    I am trying to create this QT gui using a thread but no luck. Below is my code. Problem is gui never shows up. But if i put QApplication app(m.s_argc,m.s_argv); //object instantiation guiClass *gui = new guiClass(); //show gui gui-show(); app.exec(); in main() then it works. /*INCLUDES HERE... .... */ using namespace std; struct mainStruct { int s_argc; char ** s_argv; }; typedef struct mainStruct mas; void *guifunc(void * arg); int main(int argc, char * argv[]) { mas m; m.s_argc = argc; m.s_argv = argv; pthread_t threadGUI; //start a new thread for gui int result = pthread_create(&threadGUI, NULL, guifunc, (void *) &m); if (result) { printf("Error creating gui thread"); exit(0); } return 0; } void *guifunc(void * arg) { mas m = *(mas *)arg; QApplication app(m.s_argc,m.s_argv); //object instantiation guiClass *gui = new guiClass(); //show gui gui-show(); app.exec(); }

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  • Strange compilation error on reference passing argument to function

    - by Grewdrewgoo Goobergabbsoen
    Here's the code: #include <iostream> using namespace std; void mysize(int &size, int size2); int main() { int *p; int val; p = &val; cout << p; mysize(&val, 20); // Error is pointed here! } void mysize(int &size, int size2) { cout << sizeof(size); size2 = size2 + 6000; cout << size2; } Here's the error output from GCC: In function 'int main()': Line 10: error: invalid initialization of non-const reference of type 'int&' from a temporary of type 'int*' compilation terminated due to -Wfatal-errors. What does that imply? I do not understand the error message ... invalid initialization of a non-constant? I declared the prototype function above with two parameters to take, one a reference of an integer and one just an integer value itself. I passed the reference of the int (see line 10), yet this error keeps being thrown at me. What is the issue?

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  • How does object of sub-class record information about its super-class the in a Virtual Inheritance

    - by Summer_More_More_Tea
    Hi there: I encounter this problem when tackling with virtual inheritance. I remember that in a non-virtual inheritance hierarchy, object of sub-class hold an object of its direct super-class. What about virtual inheritance? In this situation, does object of sub-class hold an object of its super-class directly or just hold a pointer pointing to an object of its super-class? By the way, why the output of the following code is: sizeof(A): 8 sizeof(B): 20 sizeof(C): 32 Code: #include <iostream> using namespace std; class A{ char k[ 3 ]; public: virtual void a(){}; }; class B : public virtual A{ char j[ 3 ]; public: virtual void b(){}; }; class C : public virtual B{ char i[ 3 ]; public: virtual void c(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; return 0; } Thanks in advance. Kind regards.

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  • Creating a new object destroys an older object with different name in C++

    - by Mikael
    First question here! So, I am having some problems with pointers in Visual C++ 2008. I'm writing a program which will control six cameras and do some processing on them so to clean things up I have created a Camera Manager class. This class handles all operations which will be carried out on all the cameras. Below this is a Camera class which interacts with each individual camera driver and does some basic image processing. Now, the idea is that when the manager is initialised it creates two cameras and adds them to a vector so that I can access them later. The catch here is that when I create the second camera (camera2) the first camera's destructor is called for some reason, which then disconnects the camera. Normally I'd assume that the problem is somewhere in the Camera class, but in this case everything works perfectly as long as I don't create the camera2 object. What's gone wrong? CameraManager.h: #include "stdafx.h" #include <vector> #include "Camera.h" class CameraManager{ std::vector<Camera> cameras; public: CameraManager(); ~CameraManager(); void CaptureAll(); void ShowAll(); }; CameraManager.cpp: #include "stdafx.h" #include "CameraManager.h" CameraManager::CameraManager() { printf("Camera Manager: Initializing\n"); [...] Camera *camera1 = new Camera(NodeInfo,1, -44,0,0); cameras.push_back(*camera1); // Adding the following two lines causes camera1's destructor to be called. Why? Camera *camera2 = new Camera(NodeInfo,0, 44,0,0); cameras.push_back(*camera2); printf("Camera Manager: Ready\n"); }

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  • Why is it that an int in C++ that isnt initialized (then used) doesn't return an error?

    - by omizzle
    I am new to C++ (just starting). I come from a Java background and I was trying out the following piece of code that would sum the numbers between 1 and 10 (inclusive) and then print out the sum: /* * File: main.cpp * Author: omarestrella * * Created on June 7, 2010, 8:02 PM */ #include <cstdlib> #include <iostream> using namespace std; int main() { int sum; for(int x = 1; x <= 10; x++) { sum += x; } cout << "The sum is: " << sum << endl; return 0; } When I ran it it kept printing 32822 for the sum. I knew the answer was supposed to be 55 and realized that its print the max value for a short (32767) plus 55. Changing int sum; to int sum = 0; would work (as it should, since the variable needs to be initialized!). Why does this behavior happen, though? Why doesnt the compiler warn you about something like this? I know Java screams at you when something isnt initialized. Thank you.

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  • C++ design related question

    - by Kotti
    Hi! Here is the question's plot: suppose I have some abstract classes for objects, let's call it Object. It's definition would include 2D position and dimensions. Let it also have some virtual void Render(Backend& backend) const = 0 method used for rendering. Now I specialize my inheritance tree and add Rectangle and Ellipse class. Guess they won't have their own properties, but they will have their own virtual void Render method. Let's say I implemented these methods, so that Render for Rectangle actually draws some rectangle, and the same for ellipse. Now, I add some object called Plane, which is defined as class Plane : public Rectangle and has a private member of std::vector<Object*> plane_objects; Right after that I add a method to add some object to my plane. And here comes the question. If I design this method as void AddObject(Object& object) I would face trouble like I won't be able to call virtual functions, because I would have to do something like plane_objects.push_back(new Object(object)); and this should be push_back(new Rectangle(object)) for rectangles and new Circle(...) for circles. If I implement this method as void AddObject(Object* object), it looks good, but then somewhere else this means making call like plane.AddObject(new Rectangle(params)); and this is generally a mess because then it's not clear which part of my program should free the allocated memory. ["when destroying the plane? why? are we sure that calls to AddObject were only done as AddObject(new something).] I guess the problems caused by using the second approach could be solved using smart pointers, but I am sure there have to be something better. Any ideas?

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  • Are C++ exceptions sufficient to implement thread-local storage?

    - by Potatoswatter
    I was commenting on an answer that thread-local storage is nice and recalled another informative discussion about exceptions where I supposed The only special thing about the execution environment within the throw block is that the exception object is referenced by rethrow. Putting two and two together, wouldn't executing an entire thread inside a function-catch-block of its main function imbue it with thread-local storage? It seems to work fine: #include <iostream> #include <pthread.h> using namespace std; struct thlocal { string name; thlocal( string const &n ) : name(n) {} }; thlocal &get_thread() { try { throw; } catch( thlocal &local ) { return local; } } void print_thread() { cerr << get_thread().name << endl; } void *kid( void *local_v ) try { thlocal &local = * static_cast< thlocal * >( local_v ); throw local; } catch( thlocal & ) { print_thread(); return NULL; } int main() try { thlocal local( "main" ); throw local; } catch( thlocal & ) { print_thread(); pthread_t th; thlocal kid_local( "kid" ); pthread_create( &th, NULL, &kid, &kid_local ); pthread_join( th, NULL ); print_thread(); return 0; } Is this novel or well-characterized? Was my initial premise correct? What kind of overhead does get_thread incur in, say, GCC and VC++? It would require throwing only exceptions derived from struct thlocal, but altogether this doesn't feel like an unproductive insomnia-ridden Sunday morning…

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  • sum of square of each elements in the vector using for_each

    - by pierr
    Hi, As the function accepted by for_each take only one parameter (the element of the vector), I have to define a static int sum = 0 somewhere so that It can be accessed after calling the for_each . I think this is awkward. Any better way to do this (still use for_each) ? #include <algorithm> #include <vector> #include <iostream> using namespace std; static int sum = 0; void add_f(int i ) { sum += i * i; } void test_using_for_each() { int arr[] = {1,2,3,4}; vector<int> a (arr ,arr + sizeof(arr)/sizeof(arr[0])); for_each( a.begin(),a.end(), add_f); cout << "sum of the square of the element is " << sum << endl; } In Ruby, We can do it this way: sum = 0 [1,2,3,4].each { |i| sum += i*i} #local variable can be used in the callback function puts sum #=> 30 Would you please show more examples how for_each is typically used in practical programming (not just print out each element)? Is it possible use for_each simulate 'programming pattern' like map and inject in Ruby (or map /fold in Haskell). #map in ruby >> [1,2,3,4].map {|i| i*i} => [1, 4, 9, 16] #inject in ruby [1, 4, 9, 16].inject(0) {|aac ,i| aac +=i} #=> 30 EDIT: Thank you all. I have learned so much from your replies. We have so many ways to do the same single thing in C++ , which makes it a little bit difficult to learn. But it's interesting :)

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  • iterators to range of elements in a vector whose attributes have specific value

    - by user1801173
    I have a vector of objects and I want to return the range of elements whose attribute have a specific value. This is the structure: class A { public: std::vector<B*> vec_; pair<vector<B*>::iterator, vector<B*>::iterator> getElements(unsigned int attr_val); unsigned int name() { return name_; } private: unsigned int name_; }; class B { public: unsigned int attr() { return attr_; } A* source() { return source_; } B* dest() { return dest_; } private: A* source_; B* dest_; unsigned int attr_; }; The vector vec_; is already sorted by attr_ and dest_-name() (in that order). Now I want to return all elements, whose attr_ is equal to attr_val. What is the appropriate stl algorithm (or is there even a vector member function?) to implement getElements(unsigned int attr_val) ? Thanks for help.

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  • How is the C++ synthesized move constructor affected by volatile and virtual members?

    - by user1827766
    Look at the following code: struct node { node(); //node(const node&); //#1 //node(node&&); //#2 virtual //#3 ~node (); node* volatile //#4 next; }; main() { node m(node()); //#5 node n=node(); //#6 } When compiled with gcc-4.6.1 it produces the following error: g++ -g --std=c++0x -c -o node.o node.cc node.cc: In constructor node::node(node&&): node.cc:3:8: error: expression node::next has side-effects node.cc: In function int main(): node.cc:18:14: note: synthesized method node::node(node&&) first required here As I understand the compiler fails to create default move or copy constructor on line #6, if I uncomment either line #1 or #2 it compiles fine, that is clear. The code compiles fine without c++0x option, so the error is related to default move constructor. However, what in the node class prevents default move constructor to be created? If I comment any of the lines #3 or #4 (i.e. make the destructor non-virtual or make data member non-volatile) it compiles again, so is it the combination of these two makes it not to compile? Another puzzle, line #5 does not cause an compilation error, what is different from line #6? Is it all specific for gcc? or gcc-4.6.1?

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  • Reverse String Error?

    - by R41nB0w M47r1z
    I am creating this revese string App but i get a error if i include a space in the string ! #include <iostream> #include <string> using namespace std; int main() { int inputa; cout<<"%%%%%%%%%%%%%%%%%%String Reversing App%%%%%%%%%%%%%%%%%%%%%%%%"<<endl<<endl; cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl; cin>>inputa; if(inputa!=0) { do { string a,c=""; cout<<"\nEnter the string you want to Reverse : "; cin>>a; for(int x=a.length()-1; x>=0; x--) { c=c+a.substr(x,1); } cout<<"\nThe Reverse String is : "<<c<<endl; cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl; cin>>inputa; } while(inputa!=0); } //not my home work } If I type the following string like "abc def" there i get an error . But otherwise it works perfectly ! Is there some mistake with the codes ! I am new to CPP so it would be helpful if you could help me !

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  • Cannot compute equation, always gives zero

    - by user1738391
    Did i miss something? The variable percentage_ always equals 0. I've checked nTimes and winnings, they give the correct values as what is being input. Even when I test out a simple equation like, percentage_=1+1, percentage_ will give 0. Can someone help? #pragma once #include <iostream> #include <string> #include <cstdlib> #include <iomanip> using namespace std; class GuessMachine { private: int nTimes; int winnings; string nM[6]; public: GuessMachine(); void displayPrizes(); void displayMenu(); int getInput(); void checkNumber(); void checkPrize(); }; void GuessMachine::checkPrize() { MagicNumber mn; int prize_=mn.generateNumber(); float percentage_; percentage_ = float (winnings/nTimes*100); //<--On this line percentage is always 0 no matter what winnings and nTimes are cout<<"Percentage is "<<percentage_<<endl; if(percentage_ >= 50) { cout<<"You have scored "<<percentage_<<"% and won "<<nM[prize_]; } else { cout<<"You have scored "<<percentage_<<"%. You lose!!"; } cin.ignore(); cin.ignore(); }

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