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• Display Fees details from database In Table Format

  - by Suryakavitha

  Hi , I am using a website(C#) for inserting fees details for I std to V std into a database... next i want to display in that details in next page as a table format which is mentioned below..... ClassName Class I ClassII ClassIII ClassIV ClassV TutionFees 1000 1000 1100 1100 1100 ExamFees 500 500 500 550 600 Bookfees 200 200 300 300 300 How shall i Do like this format? can any one tell me the solution Of this? plz.. Thanks in advance..

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• Printing factorial at compile time in C++

  - by user519882

  template<unsigned int n> struct Factorial { enum { value = n * Factorial<n-1>::value}; }; template<> struct Factorial<0> { enum {value = 1}; }; int main() { std::cout << Factorial<5>::value; std::cout << Factorial<10>::value; } above program computes factorial value during compile time. I want to print factorial value at compile time rather than at runtime using cout. How can we achive printing the factorial value at compile time? I am using VS2009. Thanks!

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• How to I count key collisions when using boost::unordered_map?

  - by Nikhil

  I have a data structure with 15 unsigned longs, I have defined a hash function using hash_combine as follows: friend std::size_t hash_value(const TUPLE15& given) { std::size_t seed = 0; boost::hash_combine(seed, val1); boost::hash_combine(seed, val2); ... return seed; } I insert a large number of values into a boost::unordered_map but the performance is not good enough. Probably, I could do better with an alternative hashing function. To confirm this, I need to check how many collisions I am getting. How do I do this?

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• Call a C++ constructor from an Objective C class

  - by syvex

  How can I call a C++ constructor from inside an Objective C class? class CppClass { public: CppClass(int arg1, const std::string& arg2): _arg1(arg1), _arg2(arg2) { } // ... private: int _arg1; std::string _arg2; }; @interface ObjC: NSObject { CppClass _cppClass; } @end @implementation ObjC - (id)init { self = [super init]; if ( self ) { // what is the syntax to call CppClass::CppClass(5, "hello") on _cppClass? } return self; } @end

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• Are volatile data members trivially copyable?

  - by Lightness Races in Orbit

  Whilst writing this answer I realised that I'm not as confident about my conclusions as I usually would ensure before hitting Post Your Answer. I can find a couple of reasonably convincing citations for the argument that the trivial-copyability of volatile data members is either implementation defined or flat-out false: https://groups.google.com/forum/?fromgroups=#!topic/comp.std.c++/5cWxmw71ktI http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48118 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3159.html#496 But I haven't been able to back this up in the standard1 itself. Particularly "worrying" is that there's no sign of the proposed wording change from that n3159 issues list in the actual standard's final wording. So, what gives? Are volatile data members trivially copyable, or not? 1   C++11

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• Why won't this static_cast in C++ work?

  - by samoz

  When I try to use a static_cast to cast a double* to an int*, I get the following error: invalid static_cast from type ‘double*’ to type ‘int*’ Here is the code: #include <iostream> int main() { double* p = new double(2); int* r; r=static_cast<int*>(p); std::cout << *r << std::endl; } I understand that there would be problems converting between a double and an int, but why is there a problem converting between a double* and an int*?

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• Pointer to another classs as a property

  - by arjacsoh

  Why I receive an error when I try to create a property to another class through a pointer like that: #ifndef SQUARE_H #define SQUARE_H #include <string> //using namespace std; #include "Player.h" class Square { public: Square(int); void process(); protected: int ID; Player* PlayerOn; <--- }; #endif and the Player class is : #ifndef PLAYER_H #define PLAYER_H #include <string> //using namespace std; #include "Square.h" class Player { public: Player(int,int); // ~Player(void); int playDice(); private: int ID; int money; }; #endif I receive: syntax error missing ; before * (on the declaration of Player* PlayerOn;) and missing type specifier (on the same line...)

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• allocator with no template

  - by Merni

  Every stl container take an allocator as a second object, template < class T, class Allocator = allocator<T> > class vector; If you write your own class It is possible to use your own allocator. But is it possible to write your own allocator without using templates? For example, writing this function is not easy if you are not allowed to use templates pointer allocate(size_type n, const_pointer = 0) { void* p = std::malloc(n * sizeof(T)); if (!p) throw std::bad_alloc(); return static_cast<pointer>(p); } Because how could you know the size of T?

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• C++ how can I refactor this?

  - by ShaChris23

  I have the code below in my test code in many places: // // Make a function call while expecting an exception should be thrown // bool exceptionThrown = false; try { expectNotEqual(someData, anotherData, methodName); } catch(std::logic_error&) { exceptionThrown = true; } if(!exceptionThrown) throw std::logic_error(methodName+"exception not thrown"); It would be nice (more readable, concise) if I could encapsulate all that, and do something like: exceptionShouldBeThrown(expectNotEqual(someData, anotherData, methodName)); I dont want to use macro ...does anyone know how I could achieve the one-liner above with C++?

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• How do I insert format str and don't remove the matched regular expression in input string in boost:

  - by Yadollah

  I want to put space between punctuations and other words in a sentence. But boost::regex_replace() replaces the punctuation with space, and I want to keep a punctuation in the sentence! for example in this code the output should be "Hello . hi , " regex e1("[.,]"); std::basic_string<char> str = "Hello.hi,"; std::basic_string<char> fmt = " "; cout<<regex_replace(str, e1, fmt)<<endl; Can you help me?

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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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• toupper/tolower + locale (german)

  - by Oops

  Hi, how to convert a string (wstring) from lowercase to uppercase characters and vice versa? I searched the net and found there is a STL-function std::transform. But until now I hav'nt figured out how to give the right locale-object for example "Germany_german" to the function. Who can help please? my code looks like: wstring strin = L"ABCÄÖÜabcäöü"; wstring str = strin; locale loc( "Germany_german" ); // ??? how to apply this ??? std::transform( str.begin(), str.end(), str.begin(), (int(*)(int)tolower ); //result: "abcäöüabcäöü" The characters ÄÖÜ and äöü (it's like Ae, Oe, Ue) will not be converted correctly. P.S.: I don't prefer a big switch sweat and also I know BOOST is capable of everything, i would prefer a STL solution. thanks in advance Oops

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• how to get stl map to construct/destruct inserted object only once.

  - by Alberto Toglia

  I have found a very prejudicial fact about stl maps. For some reason I cant get objects being inserted in the map to get constructed/destructed only once. Example: struct MyObject{ MyObject(){ cout << "constructor" << endl; } ~MyObject(){ cout << "destructor" << endl; } }; int main() { std::map<int, MyObject> myObjectsMap; myObjectsMap[0] = MyObject(); return 0; } returns: constructor destructor destructor constructor destructor If I do: typedef std::pair<int, MyObject> MyObjectPair; myObjectsMap.insert( MyObjectPair(0,MyObject())); returns: constructor destructor destructor destructor I'm inserting Objects responsible for their own memory allocation, so when destructed they'll clean themselves up, being destructed several times is causing me some trouble.

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• Is there a 'catch' with FastFormat?

  - by Roddy

  I just read about the FastFormat C++ i/o formatting library, and it seems too good to be true: Faster even than printf, typesafe, and with what I consider a pleasing interface: // prints: "This formats the remaining arguments based on their order - in this case we put 1 before zero, followed by 1 again" fastformat::fmt(std::cout, "This formats the remaining arguments based on their order - in this case we put {1} before {0}, followed by {1} again", "zero", 1); // prints: "This writes each argument in the order, so first zero followed by 1" fastformat::write(std::cout, "This writes each argument in the order, so first ", "zero", " followed by ", 1); This looks almost too good to be true. Is there a catch? Have you had good, bad or indifferent experiences with it? CW on this question, as there's probably no right answer...

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• Overriding vs Virtual

  - by anonymous

  What is the purpose of using the reserved word virtual in front of functions? If I want a child class to override a parent function, I just declare the same function such as "void draw(){}". class Parent{ public: void say(){ std::cout << "1"; }}; class Child : public Parent{public:void say(){ std::cout << "2"; } }; int main() { Child* a = new Child(); a->say(); return 0; } The output is 2. So again, why would the reserved word "virtual" be necessary in the header of say() ? Thanks a bunch.

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• [C++] Boost test: catch user defined exceptions

  - by user231536

  If I have user defined exceptions in my code, I can't get Boost test to consider them as failures. For example, BOOST_AUTO_TEST_CASE_EXPECTED_FAILURES(MyTest,1) BOOST_AUTO_TEST_CASE(MyTest) { // code which throws user defined exception, not derived from std::exception. } I get a generic message: Caught exception: .... unknown location(0):.... It does not recognize this error as a failure since it is not a std::exception. So it does not honor the expected_failures clause. How do I enforce that the piece of code should always throw an exception? THis seems to be a useful thing to want. In case future code changes cause the code to pass and the exception is not thrown, I want to know that.

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• priority_queue with dynamic priorities

  - by Layne

  Hey, I have a server application which accepts incomming queries and executes them. If there are too many queries they should be queued and if some of the other queries got executed the queued queries should be executed as well. Since I want to pass queries with different priorities I think using a priority_queue would be the best choice. e.g. The amout of the axcepting queries (a) hit the limt and new queries will be stored in the queue. All queries have a priority of 1 (lowest) if some of the queries from (a) get executed the programm will pick the query with the highest priority out of the queue and execute it. Still no problem. Now someone is sending a query with a priority of 5 which gets added to the queue. Since this is the query with the highest priority the application will execute this query as soon as the running queries no longer hit the limit. There might be the worst case that 500 queries with a priority of 1 are queued but wont be executed since someone is always sending queries with a priority of 5 hence these 500 queries will be queued for a looooong time. In order to prevent that I want to increase the prioritiy of all queries which have a lower priority than the query with the higher priority, in this example which have a priority lower than 5. So if the query with a priority of 5 gets pulled out of the queue all other queries with a priority < 5 should be increased by 0.2. This way queries with a low priority wont be queued for ever even if there might be 100 queries with a higher priority. I really hope can help me to solve the problem with the priorities: Since my queries consist of an object I thought something like this might work: class Query { public: Query( std::string p_stQuery ) : stQuery( p_stQuery ) {}; std::string getQuery() const {return stQuery;}; void increasePriority( const float fIncrease ) {fPriority += fIncrease;}; friend bool operator < ( const Query& PriorityFirst, const Query& PriorityNext ) { if( PriorityFirst.fPriority < PriorityNext.fPriority ) { if( PriorityFirst.fStartPriority < PriorityNext.fStartPriority ) { Query qTemp = PriorityFirst; qTemp.increasePriority( INCREASE_RATE ); } return true; } else { return false; } }; private: static const float INCREASE_RATE = 0.2; float fPriority; // current priority float fStartPriority; // initialised priority std::string stQuery; };

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• How to check whether iterators form a contiguous memory zone?

  - by Vincent

  I currently have the following function to read an array or a vector of raw data (_readStream is a std::ifstream) : template<typename IteratorType> inline bool MyClass::readRawData( const IteratorType& first, const IteratorType& last, typename std::iterator_traits<IteratorType>::iterator_category* = nullptr ) { _readStream.read(reinterpret_cast<char*>(&*first), (last-first)*sizeof(*first)); return _readStream.good(); } First question : does this function seem ok for you ? As we read directly a block of memory, it will only work if the memory block from first to last is contiguous in memory. How to check that ?

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• Mixing C and C++, raw pointers and (boost) shared pointers

  - by oompahloompah

  I am working in C++ with some legacy C code. I have a data structure that (during initialisation), makes a copy of the structure pointed to a ptr passed to its initialisation pointer. Here is a simplification of what I am trying to do - hopefully, no important detail has been lost in the "simplification": /* C code */ typedef struct MyData { double * elems; unsigned int len; }; int NEW_mydata(MyData* data, unsigned int len) { // no error checking data->elems = (double *)calloc(len, sizeof(double)); return 0; } typedef struct Foo { MyData data data_; }; void InitFoo(Foo * foo, const MyData * the_data) { //alloc mem etc ... then assign the STRUCTURE foo.data_ = *thedata ; } C++ code ------------- typedef boost::shared_ptr<MyData> MyDataPtr; typedef std::map<std::string, MyDataPtr> Datamap; class FooWrapper { public: FooWrapper(const std::string& key) { MyDataPtr mdp = dmap[key]; InitFoo(&m_foo, const_cast<MyData*>((*mdp.get()))); } ~FooWrapper(); double get_element(unsigned int index ) const { return m_foo.elems[index]; } private: // non copyable, non-assignable FooWrapper(const FooWrapper&); FooWrapper& operator= (const FooWrapper&); Foo m_foo; }; int main(int argc, char *argv[]) { MyData data1, data2; Datamap dmap; NEW_mydata(&data1, 10); data1->elems[0] = static_cast<double>(22/7); NEW_mydata(&data2, 42); data2->elems[0] = static_cast<double>(13/21); boost::shared_ptr d1(&data1), d2(&data2); dmap["data1"] = d1; dmap["data2"] = d2; FooWrapper fw("data1"); //expect 22/7, get something else (random number?) double ret fw.get_element(0); } Essentially, what I want to know is this: Is there any reason why the data retrieved from the map is different from the one stored in the map?

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• How to pass parameters with spaces via cstdlib system

  - by buchtak

  Hi, I have this windows console app which takes a file, do some calculations, and then writes the output to a specified file. The input is specified in "app.exe -input fullfilename" format. I need to call this application from my C++ program, but I have a problem with spaces in paths to files. When I call the app directly from cmd.exe by typing (without specifying output file for clarity) "c:\first path\app.exe" -input "c:\second path\input.file" everything works as expected. But, when I try using cstdlib std::system() function, i.e. std::system(" \"c:\\first path\\app.exe\" -input \"c:\\second path\\input.file\" "); the console prints out that c:\first is not any valid command. It's probably common mistake and has simple solution, but I have been unable to find any. Thx for any help.

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• How to replace all occurrences of a character in string?

  - by zilgo

  What is the effective way to replace all occurrences of a character with another character in std::string?

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• Running for loop depending on size of string vector

  - by xbonez

  I have made a string vector vector actor_; and then added elements in it using push_back. I now want to display all of them, for which I need to run a loop according to the number of elements in the vector. For that, I need to run the following loop: for (int i = 0; i < (int)actor_.size; i++) { } but this returns the following error: error C2440: 'type cast' : cannot convert from 'unsigned int (__thiscall std::vector<_Ty::* )(void) const' to 'int' 1 with 1 [ 1 _Ty=std::string 1 ] 1 There is no context in which this conversion is possible

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• How to make a rectangle on screen invisible to screen capture ?

  - by Kesarion

  How can I create a rectangle on the screen that is invisible to any sort of screen capture(printscreen or aplications) ? By create a rectangle on screen I mean something like this: #include <Windows.h> #include <iostream> void drawRect(){ HDC screenDC = ::GetDC(0); ::Rectangle(screenDC, 200, 200, 300, 300); ::ReleaseDC(0, screenDC); } int main(void){ char c; std::cin >> c; if (c == 'd') drawRect(); std::cin >> c; return 0; } I'm using Visual Studio 2010 on Windows XP

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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++ - Error: expected unqualified-id before ‘using’

  - by Francisco P.

  Hello, everyone. I am having some trouble on a project I'm working on. Here's the header file for the calor class: #ifndef _CALOR_ #define _CALOR_ #include "gradiente.h" using namespace std; class Calor : public Gradiente { public: Calor(); Calor(int a); ~Calor(); int getTemp(); int getMinTemp(); void setTemp(int a); void setMinTemp(int a); void mostraSensor(); }; #endif When I try to compile it: calor.h|6|error: expected unqualified-id before ‘using’| Why does this happen? I've been searching online and learned this error occurs mostly due to corrupted included files. Makes no sense to me, though. This class inherits from gradiente: #ifndef _GRADIENTE_ #define _GRADIENTE_ #include "sensor.h" using namespace std; class Gradiente : public Sensor { protected: int vActual, vMin; public: Gradiente(); ~Gradiente(); } #endif Which in turn inherits from sensor #ifndef _SENSOR_ #define _SENSOR_ #include <iostream> #include <fstream> #include <string> #include "definicoes.h" using namespace std; class Sensor { protected: int tipo; int IDsensor; bool estadoAlerta; bool estadoActivo; static int numSensores; public: Sensor(/*PARAMETROS*/); Sensor(ifstream &); ~Sensor(); int getIDsensor(); bool getEstadoAlerta(); bool getEstadoActivo(); void setEstadoAlerta(int a); void setEstadoActivo(int a); virtual void guardaSensor(ofstream &); virtual void mostraSensor(); // FUNÇÃO COMUM /* virtual int funcaoComum() = 0; virtual int funcaoComum(){return 0;};*/ }; #endif For completeness' sake, here's definicoes.h #ifndef _DEFINICOES_ #define _DEFINICOES_ const unsigned int SENSOR_MOVIMENTO = 0; const unsigned int SENSOR_SOM = 1; const unsigned int SENSOR_PRESSAO = 2; const unsigned int SENSOR_CALOR = 3; const unsigned int SENSOR_CONTACTO = 4; const unsigned int MIN_MOVIMENTO = 10; const unsigned int MIN_SOM = 10; const unsigned int MIN_PRESSAO = 10; const unsigned int MIN_CALOR = 35; #endif Any help'd be much appreciated. Thank you for your time. Thanks for your time!

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