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• why is my 3n+1 problem solution wrong?

  - by nunos

  I have recently started reading "Programming Challenges" book by S. Skiena and believe or not I am kind of stuck in the very first problem. Here's a link to the problem: 3n+1 problem Here's my code: #include <iostream> #include <vector> #include <algorithm> using namespace std; unsigned long calc(unsigned long n); int main() { int i, j, a, b, m; vector<int> temp; while (true) { cin >> i >> j; if (cin.fail()) break; if (i < j) { a = i; b = j; } else { a = j; b = i; } temp.clear(); for (unsigned int k = a; k != b; k++) { temp.push_back(calc(k)); } m = *max_element(temp.begin(), temp.end()); cout << i << ' ' << j << ' ' << m << endl; } } unsigned long calc(unsigned long n) { unsigned long ret = 1; while (n != 1) { if (n % 2 == 0) n = n/2; else n = 3*n + 1; ret++; } return ret; } I know the code is inefficient and I should not be using vectors to store the data. Anyway, I still would like to know what it's wrong with this, since, for me, it makes perfect sense, even though I am getting WA (wrong answer at programming challenges judge and RE (Runtime Error) at UVa judge). Thanks.

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• Timestamp issue with localtime and mktime

  - by egiakoum1984

  Please see the code below: #include <iostream> #include <stdlib.h> #include <time.h> using namespace std; int main(void) { time_t current_time = 1270715952; cout << "Subscriber current timestamp:" << current_time << endl; tm* currentTm = localtime(&current_time); char tmp_str[256]; //2010-04-08T11:39:12 snprintf(tmp_str, sizeof(tmp_str), "%04d%02d%02d%02d%02d%02d.000", currentTm->tm_year+1900, currentTm->tm_mon+1, currentTm->tm_mday, currentTm->tm_hour, currentTm->tm_min, currentTm->tm_sec); cout << "Subscriber current date:" << tmp_str << endl; tm tmpDateScheduleFrom, tmpDateScheduleTo; memset(&tmpDateScheduleFrom, 0, sizeof(tm)); memset(&tmpDateScheduleTo, 0, sizeof(tm)); //2010-04-08T11:00 tmpDateScheduleFrom.tm_sec = 0; tmpDateScheduleFrom.tm_min = 0; tmpDateScheduleFrom.tm_hour = 11; tmpDateScheduleFrom.tm_mday = 8; tmpDateScheduleFrom.tm_mon = 3; tmpDateScheduleFrom.tm_year = 110; //2010-04-08T12:00 tmpDateScheduleTo.tm_sec = 0; tmpDateScheduleTo.tm_min = 0; tmpDateScheduleTo.tm_hour = 12; tmpDateScheduleTo.tm_mday = 8; tmpDateScheduleTo.tm_mon = 3; tmpDateScheduleTo.tm_year = 110; time_t localFrom = mktime(&tmpDateScheduleFrom); time_t localTo = mktime(&tmpDateScheduleTo); cout << "Subscriber current timestamp:" << current_time << endl; cout << "Subscriber localFrom:" << localFrom << endl; cout << "Subscriber localTo:" << localTo << endl; return 0; } The results are the following: Subscriber current timestamp:1270715952 Subscriber current date:20100408113912.000 Subscriber current timestamp:1270715952 Subscriber localFrom:1270717200 Subscriber localTo:1270720800 Why the current subscriber timestamp (subscriber date and time: 2010-04-08T11:39:12) is not between the range localFrom (timestamp of date/time: 2010-04-08T11:00:00) and LocalTo (timestamp of date/time: 2010-04-08T12:00:00)?

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• Finite State Machine Spellchecker

  - by Durell

  I would love to have a debugged copy of the finite state machine code below. I tried debugging but could not, all the machine has to do is to spell check the word "and",an equivalent program using case is welcomed. #include<cstdlib> #include<stdio.h> #include<string.h> #include<iostream> #include<string> using namespace std; char in_str; int n; void spell_check() { char data[256]; int i; FILE *in_file; in_file=fopen("C:\\Users\\mytorinna\\Desktop\\a.txt","r+"); while (!feof(in_file)) { for(i=0;i<256;i++) { fscanf(in_file,"%c",in_str); data[i]=in_str; } //n = strlen(in_str); //start(data); cout<<data; } } void start(char data) { // char next_char; //int i = 0; // for(i=0;i<256;i++) // if (n == 0) { if(data[i]="a") { state_A(); exit; } else { cout<<"I am comming"; } // cout<<"This is an empty string"; // exit();//do something here to terminate the program } } void state_A(int i) { if(in_str[i] == 'n') { i++; if(i<n) state_AN(i); else error(); } else error(); } void state_AN(int i) { if(in_str[i] == 'd') { if(i == n-1) cout<<" Your keyword spelling is correct"; else cout<<"Wrong keyword spelling"; } } int main() { spell_check(); system("pause"); return 0; }

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• About fork system call and global variables

  - by lurks

  I have this program in C++ that forks two new processes: #include <pthread.h> #include <iostream> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <cstdlib> using namespace std; int shared; void func(){ extern int shared; for (int i=0; i<10;i++) shared++; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } int main(){ extern int shared; pid_t p1,p2; int status; shared=0; if ((p1=fork())==0) {func();exit(0);}; if ((p2=fork())==0) {func();exit(0);}; for(int i=0;i<10;i++) shared++; waitpid(p1,&status,0); waitpid(p2,&status,0);; cout<<"shared variable is: "<<shared<<endl; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } The two forked processes make an increment on the shared variables and the parent process does the same. As the variable belongs to the data segment of each process, the final value is 10 because the increment is independent. However, the memory address of the shared variables is the same, you can try compiling and watching the output of the program. How can that be explained ? I cannot understand that, I thought I knew how the fork() works, but this seems very odd.. I need an explanation on why the address is the same, although they are separate variables.

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• C++: compute a number's complement and its number of possible mismatches

  - by Eagle

  I got a bit stuck with my algorithm and I need some help to solve my problem. I think an example would explain better my problem. Assuming: d = 4 (maximum number of allowed bits in a number, 2^4-1=15). m_max = 1 (maximum number of allowed bits mismatches). kappa = (maximum number of elements to find for a given d and m, where m in m_max) The main idea is for a given number, x, to compute its complement number (in binary base) and all the possible combinations for up to m_max mismatches from x complement's number. Now the program start to scan from i = 0 till 15. for i = 0 and m = 0, kappa = \binom{d}{0} = 1 (this called a perfect match) possible combinations in bits, is only 1111 (for 0: 0000). for i = 0 and m = 1, kappa = \binom{d}{1} = 4 (one mismatch) possible combinations in bits are: 1000, 0100, 0010 and 0001 My problem was to generalize it to general d and m. I wrote the following code: #include <stdlib.h> #include <iomanip> #include <boost/math/special_functions/binomial.hpp> #include <iostream> #include <stdint.h> #include <vector> namespace vec { typedef std::vector<unsigned int> uint_1d_vec_t; } int main( int argc, char* argv[] ) { int counter, d, m; unsigned num_combination, bits_mask, bit_mask, max_num_mismatch; uint_1d_vec_t kappa; d = 4; m = 2; bits_mask = 2^num_bits - 1; for ( unsigned i = 0 ; i < num_elemets ; i++ ) { counter = 0; for ( unsigned m = 0 ; m < max_num_mismatch ; m++ ) { // maximum number of allowed combinations num_combination = boost::math::binomial_coefficient<double>( static_cast<unsigned>( d ), static_cast<unsigned>(m) ); kappa.push_back( num_combination ); for ( unsigned j = 0 ; j < kappa.at(m) ; j++ ) { if ( m == 0 ) v[i][counter++] = i^bits_mask; // M_0 else { bit_mask = 1 << ( num_bits - j ); v[i][counter++] = v[i][0] ^ bits_mask } } } } return 0; } I got stuck in the line v[i][counter++] = v[i][0] ^ bits_mask since I was unable to generalize my algorithm to m_max1, since I needed for m_max mismatches m_max loops and in my original problem, m is unknown until runtime.

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• operator+ overload returning object causing memory leaks, C++

  - by lampshade

  The problem i think is with returing an object when i overload the + operator. I tried returning a reference to the object, but doing so does not fix the memory leak. I can comment out the two statements: dObj = dObj + dObj2; and cObj = cObj + cObj2; to free the program of memory leaks. Somehow, the problem is with returning an object after overloading the + operator. #include <iostream> #include <vld.h> using namespace std; class Animal { public : Animal() {}; virtual void eat() = 0 {}; virtual void walk() = 0 {}; }; class Dog : public Animal { public : Dog(const char * name, const char * gender, int age); Dog() : name(NULL), gender(NULL), age(0) {}; virtual ~Dog(); Dog operator+(const Dog &dObj); private : char * name; char * gender; int age; }; class MyClass { public : MyClass() : action(NULL) {}; void setInstance(Animal &newInstance); void doSomething(); private : Animal * action; }; Dog::Dog(const char * name, const char * gender, int age) : // allocating here, for data passed in ctor name(new char[strlen(name)+1]), gender(new char[strlen(gender)+1]), age(age) { if (name) { size_t length = strlen(name) +1; strcpy_s(this->name, length, name); } else name = NULL; if (gender) { size_t length = strlen(gender) +1; strcpy_s(this->gender, length, gender); } else gender = NULL; if (age) { this->age = age; } } Dog::~Dog() { delete name; delete gender; age = 0; } Dog Dog::operator+(const Dog &dObj) { Dog d; d.age = age + dObj.age; return d; } void MyClass::setInstance(Animal &newInstance) { action = &newInstance; } void MyClass::doSomething() { action->walk(); action->eat(); } int main() { MyClass mObj; Dog dObj("Scruffy", "Male", 4); // passing data into ctor Dog dObj2("Scooby", "Male", 6); mObj.setInstance(dObj); // set the instance specific to the object. mObj.doSomething(); // something happens based on which object is passed in dObj = dObj + dObj2; // invoke the operator+ return 0; }

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• How do I destruct data associated with an object after the object no longer exists?

  - by Phineas

  I'm creating a class (say, C) that associates data (say, D) with an object (say, O). When O is destructed, O will notify C that it soon will no longer exist :( ... Later, when C feels it is the right time, C will let go of what belonged to O, namely D. If D can be any type of object, what's the best way for C to be able to execute "delete D;"? And what if D is an array of objects? My solution is to have D derive from a base class that C has knowledge of. When the time comes, C calls delete on a pointer to the base class. I've also considered storing void pointers and calling delete, but I found out that's undefined behavior and doesn't call D's destructor. I considered that templates could be a novel solution, but I couldn't work that idea out. Here's what I have so far for C, minus some details: // This class is C in the above description. There may be many instances of C. class Context { public: // D will inherit from this class class Data { public: virtual ~Data() {} }; Context(); ~Context(); // Associates an owner (O) with its data (D) void add(const void* owner, Data* data); // O calls this when he knows its the end (O's destructor). // All instances of C are now aware that O is gone and its time to get rid // of all associated instances of D. static void purge (const void* owner); // This is called periodically in the application. It checks whether // O has called purge, and calls "delete D;" void refresh(); // Side note: sometimes O needs access to D Data *get (const void *owner); private: // Used for mapping owners (O) to data (D) std::map _data; }; // Here's an example of O class Mesh { public: ~Mesh() { Context::purge(this); } void init(Context& c) const { Data* data = new Data; // GL initialization here c.add(this, new Data); } void render(Context& c) const { Data* data = c.get(this); } private: // And here's an example of D struct Data : public Context::Data { ~Data() { glDeleteBuffers(1, &vbo); glDeleteTextures(1, &texture); } GLint vbo; GLint texture; }; }; P.S. If you're familiar with computer graphics and VR, I'm creating a class that separates an object's per-context data (e.g. OpenGL VBO IDs) from its per-application data (e.g. an array of vertices) and frees the per-context data at the appropriate time (when the matching rendering context is current).

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• compiling a program to run in DOS mode

  - by dygi

  I write a simple program, to run in DOS mode. Everything works under emulated console in Win XP / Vista / Seven, but not in DOS. The error says: this program caonnot be run in DOS mode. I wonder is that a problem with compiler flags or something bigger. For programming i use Code::Blocks v 8.02 with such settings for compilation: -Wall -W -pedantic -pedantic-errors in Project \ Build options \ Compiler settings I've tried a clean DOS mode, booting from cd, and also setting up DOS in Virtual Machine. The same error appears. Should i turn on some more compiler flags ? Some specific 386 / 486 optimizations ? UPDATE Ok, i've downloaded, installed and configured DJGPP. Even resolved some problems with libs and includes. Still have two questions. 1) i can't compile a code, which calls _strdate and _strtime, i've double checked the includes, as MSDN says it needs time.h, but still error says: _strdate was not declared in this scope, i even tried to add std::_strdate, but then i have 4, not 2 errors sazing the same 2) the 2nd code is about gotoxy, it looks like that: #include <windows.h> void gotoxy(int x, int y) { COORD position; position.X = x; position.Y = y; SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), position); } error says there is no windows.h, so i've put it in place, but then there are many more errors saying some is missing from windows.h, I SUPPOSE it won't work because this functions is strictly for windows right ? is there any way to write similar gotoxy for DOS ? UPDATE2 1) solved using time(); instead of _strdate(); and _strtime(); here's the code time_t rawtime; struct tm * timeinfo; char buffer [20]; time ( &rawtime ); timeinfo = localtime ( &rawtime ); strftime (buffer,80,"%Y.%m.%d %H:%M:%S\0",timeinfo); string myTime(buffer); It now compiles under DJGPP. UPDATE3 Still need to solve a code using gotoxy - replaced it with some other code that compiles (under DJGPP). Thank You all for help. Just learnt some new things about compiling (flags, old IDE's like DJGPP, OpenWatcom) and refreshed memories setting DOS to work :--)

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• An interesting case of delete and destructor (C++)

  - by Viet

  I have a piece of code where I can call destructor multiple times and access member functions even the destructor was called with member variables' values preserved. I was still able to access member functions after I called delete but the member variables were nullified (all to 0). And I can't double delete. Please kindly explain this. Thanks. #include <iostream> using namespace std; template <typename T> void destroy(T* ptr) { ptr->~T(); } class Testing { public: Testing() : test(20) { } ~Testing() { printf("Testing is being killed!\n"); } int getTest() const { return test; } private: int test; }; int main() { Testing *t = new Testing(); cout << "t->getTest() = " << t->getTest() << endl; destroy(t); cout << "t->getTest() = " << t->getTest() << endl; t->~Testing(); cout << "t->getTest() = " << t->getTest() << endl; delete t; cout << "t->getTest() = " << t->getTest() << endl; destroy(t); cout << "t->getTest() = " << t->getTest() << endl; t->~Testing(); cout << "t->getTest() = " << t->getTest() << endl; //delete t; // <======== Don't do it! Double free/delete! cout << "t->getTest() = " << t->getTest() << endl; return 0; }

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• Using a function with reference as a function with pointers?

  - by epatel

  Today I stumbled over a piece of code that looked horrifying to me. The pieces was chattered in different files, I have tried write the gist of it in a simple test case below. The code base is routinely scanned with FlexeLint on a daily basis, but this construct has been laying in the code since 2004. The thing is that a function implemented with a parameter passing using references is called as a function with a parameter passing using pointers...due to a function cast. The construct has worked since 2004 on Irix and now when porting it actually do work on Linux/gcc too. My question now. Is this a construct one can trust? I can understand if compiler constructors implement the reference passing as it was a pointer, but is it reliable? Are there hidden risks? Should I change the fref(..) to use pointers and risk braking anything in the process? What to you think? #include <iostream> using namespace std; // ---------------------------------------- // This will be passed as a reference in fref(..) struct string_struct { char str[256]; }; // ---------------------------------------- // Using pointer here! void fptr(const char *str) { cout << "fptr: " << str << endl; } // ---------------------------------------- // Using reference here! void fref(string_struct &str) { cout << "fref: " << str.str << endl; } // ---------------------------------------- // Cast to f(const char*) and call with pointer void ftest(void (*fin)()) { void (*fcall)(const char*) = (void(*)(const char*))fin; fcall("Hello!"); } // ---------------------------------------- // Let's go for a test int main() { ftest((void (*)())fptr); // test with fptr that's using pointer ftest((void (*)())fref); // test with fref that's using reference return 0; }

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• find window text and save txt to file named that wont work.

  - by blood

  hi, my code wont work and idk why. the point of my code is to find the top window and save a text file with the name the same as the text on the top menu bar (task bar i think?). then save some data to that text file. but everytime i try to use it the write fails if i set the name of the text file before hand so it wont change it will write the data to the file. but if i don't set it before hand it will make the text doc but not write anything to it. or sometimes it will just write numbers for the name (i think it's the handle number) then it will write the data. :\ it's odd can anyone help? #include <iostream> #include <windows.h> #include <fstream> #include <string> #include <sstream> #include <time.h> using namespace std; string header_str = ("NULL"); #define DTTMFMT "%Y-%m-%d %H:%M:%S " #define DTTMSZ 21 char buff[DTTMSZ]; fstream filestr; string ff = ("C:\\System logs\\txst.txt"); TCHAR buf[255]; int main() { GetWindowText(GetForegroundWindow(), buf, 255); stringstream header(stringstream::in | stringstream::out); header.flush(); header << ("C:\\System logs\\"); header << buf; header << (".txt"); header_str = header.str(); ff = header_str; cout << header_str << "\n"; filestr.open (ff.c_str(), fstream::in | fstream::out | fstream::app | ios_base::binary | ios_base::out); filestr << "dfg"; filestr.close(); Sleep(10000); return 0; }

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• Possible bug with tabified QDockWidget and setFloating()

  - by krunk

  I've run into some odd behavior with tabified QDockWidgets, below is an example program with comments that demonstrates the behavior. Is this a bug or is it expected behavior and I'm missing some nuance in QDockWidget that causes this? Directly, since this does not work, how would one properly "undock" a hidden QDockWidget then display it? #include <QApplication> #include <QMainWindow> #include <QAction> #include <QDockWidget> #include <QMenu> #include <QSize> #include <QMenuBar> using namespace std; int main (int argc, char* argv[]) { QApplication app(argc, argv); QMainWindow window; QDockWidget dock1(&window); QDockWidget dock2(&window); QMenu menu("View"); dock1.setAllowedAreas(Qt::LeftDockWidgetArea | Qt::RightDockWidgetArea); dock2.setAllowedAreas(Qt::LeftDockWidgetArea | Qt::RightDockWidgetArea); dock1.setWindowTitle("Dock One"); dock2.setWindowTitle("Dock Two"); window.addDockWidget(Qt::RightDockWidgetArea, &dock1); window.addDockWidget(Qt::RightDockWidgetArea, &dock2); window.menuBar()->addMenu(&menu); window.setMinimumSize(QSize(800, 600)); window.tabifyDockWidget(&dock1, &dock2); dock1.hide(); dock2.hide(); menu.addAction(dock1.toggleViewAction()); menu.addAction(dock2.toggleViewAction()); window.show(); // Below is where the oddness starts. It seems to only exhibit the // behavior if the dock widgets are tabified. // Odd behavior here // This does not work. the window never shows, though its menu action shows // checked. Not only does this window not show up, but all toggle actions // for all dock windows (e.g. dock1 and dock2) are broken for the duration // of the application loop. // dock1.setFloating(true); // dock1.show(); // This does work. . . of course only if you do _not_ run the above first. // however, you can often get a little lag or "blip" in the rendering as // the dock is shown docked before setFloating is set to true. dock1.show(); dock1.setFloating(true); return app.exec(); }

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• Problem compiling c++ in CodeGear

  - by Carlos

  I have written a C++ program for a University assignment. I used Netbeans 6.8 running on my Mac and the code runs smoothly, no warnings, errors or problems/bugs. However when compiling and running on a Windows computer using CodeGear RAD Studio 2009 (C++ Builder) am getting several errors. [BCC32 Error] main.cpp(51): E2094 'operator<<' not implemented in type 'ostream' for arguments of type 'string' [BCC32 Error] main.cpp(62): E2093 'operator==' not implemented in type 'string' for arguments of the same type [BCC32 Error] main.cpp(67): E2093 'operator==' not implemented in type 'string' for arguments of the same type [BCC32 Error] main.cpp(112): E2093 'operator==' not implemented in type 'string' for arguments of the same type [BCC32 Error] main.cpp(121): E2094 'operator<<' not implemented in type 'ostream' for arguments of type 'string' [BCC32 Error] main.cpp(130): E2093 'operator==' not implemented in type 'string' for arguments of the same type [BCC32 Error] main.cpp(133): E2094 'operator<<' not implemented in type 'ostream' for arguments of type 'string' [BCC32 Error] main.cpp(139): E2094 'operator<<' not implemented in type 'ostream' for arguments of type 'string' [BCC32 Error] main.cpp(153): E2094 'operator<<' not implemented in type 'fstream' for arguments of type 'string' [BCC32 Error] main.cpp(199): E2094 'operator>>' not implemented in type 'fstream' for arguments of type 'string' [BCC32 Error] main.cpp(219): E2094 'operator>>' not implemented in type 'istream' for arguments of type 'string' [BCC32 Error] main.cpp(231): E2094 'operator>>' not implemented in type 'istream' for arguments of type 'string' [BCC32 Error] main.cpp(240): E2094 'operator>>' not implemented in type 'istream' for arguments of type 'string' [BCC32 Error] main.cpp(262): E2094 'operator>>' not implemented in type 'istream' for arguments of type 'string' [BCC32 Error] main.cpp(264): E2094 'operator>>' not implemented in type 'istream' for arguments of type 'string' These are the header files am using #include <iostream> #include <fstream> #include <cmath> #include <stdio> #include <windows> //I added this one just to check and still does not work (I didnt have it on Netbeans/Mac) using namespace std; Any ideas what is producing the errors and how can I fix it?

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• QValidator for hex input

  - by Evan Teran

  I have a Qt widget which should only accept a hex string as input. It is very simple to restrict the input characters to [0-9A-Fa-f], but I would like to have it display with a delimiter between "bytes" so for example if the delimiter is a space, and the user types 0011223344 I would like the line edit to display 00 11 22 33 44 Now if the user presses the backspace key 3 times, then I want it to display 00 11 22 3. I almost have what i want, so far there is only one subtle bug involving using the delete key to remove a delimiter. Does anyone have a better way to implement this validator? Here's my code so far: class HexStringValidator : public QValidator { public: HexStringValidator(QObject * parent) : QValidator(parent) {} public: virtual void fixup(QString &input) const { QString temp; int index = 0; // every 2 digits insert a space if they didn't explicitly type one Q_FOREACH(QChar ch, input) { if(std::isxdigit(ch.toAscii())) { if(index != 0 && (index & 1) == 0) { temp += ' '; } temp += ch.toUpper(); ++index; } } input = temp; } virtual State validate(QString &input, int &pos) const { if(!input.isEmpty()) { // TODO: can we detect if the char which was JUST deleted // (if any was deleted) was a space? and special case this? // as to not have the bug in this case? const int char_pos = pos - input.left(pos).count(' '); int chars = 0; fixup(input); pos = 0; while(chars != char_pos) { if(input[pos] != ' ') { ++chars; } ++pos; } // favor the right side of a space if(input[pos] == ' ') { ++pos; } } return QValidator::Acceptable; } }; For now this code is functional enough, but I'd love to have it work 100% as expected. Obviously the ideal would be the just separate the display of the hex string from the actual characters stored in the QLineEdit's internal buffer but I have no idea where to start with that and I imagine is a non-trivial undertaking. In essence, I would like to have a Validator which conforms to this regex: "[0-9A-Fa-f]( [0-9A-Fa-f])*" but I don't want the user to ever have to type a space as delimiter. Likewise, when editing what they types, the spaces should be managed implicitly.

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• Cpp some basic problems

  - by DevAno1

  Hello. My task was as follows : Create class Person with char*name and int age. Implement contructor using dynamic allocation of memory for variables, destructor, function init and friend function show. Then transform this class to header and cpp file and implement in other program. Ok so I've almost finished my Person class, but I get error after destructor. First question is how to write this properly ? #include <iostream> using namespace std; class Person { char* name; int age; public: int * take_age(); Person(){ int size=0; cout << "Give length of char*" << endl; cin >> size; name = new char[size]; age = 0; } ~Person(){ cout << "Destroying resources" << endl; delete *[] name; delete * take_age(); } friend void(Person &p); int * Person::take_age(){ return age; } void init(char* n, int a) { name = n; age = a; } void show(Person &p){ cout << "Name: " << p.name << "," << "age: " << p.age << endl; } }; int main(void) { Person *p = new Person; p->init("Mary", 25); p.show(); system("PAUSE"); return 0; } And now with header/implementation part : - do I need to introduce constructor in header/implementation files ? If yes - how? - my show() function is a friendly function. Should I take it into account somehow ? I already failed to return this task on my exam, but still I'd like to know how to implement it.

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• Mocking a concrete class : templates and avoiding conditional compilation

  - by AshirusNW

  I'm trying to testing a concrete object with this sort of structure. class Database { public: Database(Server server) : server_(server) {} int Query(const char* expression) { server_.Connect(); return server_.ExecuteQuery(); } private: Server server_; }; i.e. it has no virtual functions, let alone a well-defined interface. I want to a fake database which calls mock services for testing. Even worse, I want the same code to be either built against the real version or the fake so that the same testing code can both: Test the real Database implementation - for integration tests Test the fake implementation, which calls mock services To solve this, I'm using a templated fake, like this: #ifndef INTEGRATION_TESTS class FakeDatabase { public: FakeDatabase() : realDb_(mockServer_) {} int Query(const char* expression) { MOCK_EXPECT_CALL(mockServer_, Query, 3); return realDb_.Query(); } private: // in non-INTEGRATION_TESTS builds, Server is a mock Server with // extra testing methods that allows mocking Server mockServer_; Database realDb_; }; #endif template <class T> class TestDatabaseContainer { public: int Query(const char* expression) { int result = database_.Query(expression); std::cout << "LOG: " << result << endl; return result; } private: T database_; }; Edit: Note the fake Database must call the real Database (but with a mock Server). Now to switch between them I'm planning the following test framework: class DatabaseTests { public: #ifdef INTEGRATION_TESTS typedef TestDatabaseContainer<Database> TestDatabase ; #else typedef TestDatabaseContainer<FakeDatabase> TestDatabase ; #endif TestDatabase& GetDb() { return _testDatabase; } private: TestDatabase _testDatabase; }; class QueryTestCase : public DatabaseTests { public: void TestStep1() { ASSERT(GetDb().Query(static_cast<const char *>("")) == 3); return; } }; I'm not a big fan of that compile-time switching between the real and the fake. So, my question is: Whether there's a better way of switching between Database and FakeDatabase? For instance, is it possible to do it at runtime in a clean fashion? I like to avoid #ifdefs. Also, if anyone has a better way of making a fake class that mimics a concrete class, I'd appreciate it. I don't want to have templated code all over the actual test code (QueryTestCase class). Feel free to critique the code style itself, too. You can see a compiled version of this code on codepad.

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• Using boost::iterator

  - by Neil G

  I wrote a sparse vector class (see #1, #2.) I would like to provide two kinds of iterators: The first set, the regular iterators, can point any element, whether set or unset. If they are read from, they return either the set value or value_type(), if they are written to, they create the element and return the lvalue reference. Thus, they are: Random Access Traversal Iterator and Readable and Writable Iterator The second set, the sparse iterators, iterate over only the set elements. Since they don't need to lazily create elements that are written to, they are: Random Access Traversal Iterator and Readable and Writable and Lvalue Iterator I also need const versions of both, which are not writable. I can fill in the blanks, but not sure how to use boost::iterator_adaptor to start out. Here's what I have so far: template<typename T> class sparse_vector { public: typedef size_t size_type; typedef T value_type; private: typedef T& true_reference; typedef const T* const_pointer; typedef sparse_vector<T> self_type; struct ElementType { ElementType(size_type i, T const& t): index(i), value(t) {} ElementType(size_type i, T&& t): index(i), value(t) {} ElementType(size_type i): index(i) {} ElementType(ElementType const&) = default; size_type index; value_type value; }; typedef vector<ElementType> array_type; public: typedef T* pointer; typedef T& reference; typedef const T& const_reference; private: size_type size_; mutable typename array_type::size_type sorted_filled_; mutable array_type data_; // lots of code for various algorithms... public: class sparse_iterator : public boost::iterator_adaptor< sparse_iterator // Derived , array_type::iterator // Base (the internal array) (this paramater does not compile! -- says expected a type, got 'std::vector::iterator'???) , boost::use_default // Value , boost::random_access_traversal_tag? // CategoryOrTraversal > class iterator_proxy { ??? }; class iterator : public boost::iterator_facade< iterator // Derived , ????? // Base , ????? // Value , boost::?????? // CategoryOrTraversal > { }; };

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• How do I get the next token in a Cstring if I want to use it as an int? (c++)

  - by Van

  My objective is to take directions from a user and eventually a text file to move a robot. The catch is that I must use Cstrings(such as char word[];) rather than the std::string and tokenize them for use. the code looks like this: void Navigator::manualDrive() { char uinput[1]; char delim[] = " "; char *token; cout << "Enter your directions below: \n"; cin.ignore(); cin.getline (uinput, 256); token=strtok(uinput, delim); if(token == "forward") { int inches; inches=token+1; travel(inches); } } I've never used Cstrings I've never tokenized anything before, and I don't know how to write this. Our T.A.'s expect us to google and find all the answers because they are aware we've never been taught these methods. Everyone in my lab is having much more trouble than usual. I don't know the code to write but I know what I want my program to do. I want it to execute like this: 1) Ask for directions. 2) cin.getline the users input 3) tokenize the inputed string 4) if the first word token == "forward" move to the next token and find out how many inches to move forward then move forward 5) else if the first token == "turn" move to the next token. if the next token == "left" move to the next token and find out how many degrees to turn left I will have to do this for forward x, backward x, turn left x, turn right x, and stop(where x is in inches or degrees). I already wrote functions that tell the robot how to move forward an inch and turn in degrees. I just need to know how to convert the inputted strings to all lowercase letters and move from token to token and convert or extract the numbers from the string to use them as integers. If all is not clear you can read my lab write up at this link: http://www.cs.utk.edu/~cs102/robot_labs/Lab9.html If anything is unclear please let me know, and I will clarify as best I can.

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• Idiomatic use of auto_ptr to transfer ownership to a container

  - by heycam

  I'm refreshing my C++ knowledge after not having used it in anger for a number of years. In writing some code to implement some data structure for practice, I wanted to make sure that my code was exception safe. So I've tried to use std::auto_ptrs in what I think is an appropriate way. Simplifying somewhat, this is what I have: class Tree { public: ~Tree() { /* delete all Node*s in the tree */ } void insert(const string& to_insert); ... private: struct Node { ... vector<Node*> m_children; }; Node* m_root; }; template<T> void push_back(vector<T*>& v, auto_ptr<T> x) { v.push_back(x.get()); x.release(); } void Tree::insert(const string& to_insert) { Node* n = ...; // find where to insert the new node ... push_back(n->m_children, auto_ptr<Node>(new Node(to_insert)); ... } So I'm wrapping the function that would put the pointer into the container, vector::push_back, and relying on the by-value auto_ptr argument to ensure that the Node* is deleted if the vector resize fails. Is this an idiomatic use of auto_ptr to save a bit of boilerplate in my Tree::insert? Any improvements you can suggest? Otherwise I'd have to have something like: Node* n = ...; // find where to insert the new node auto_ptr<Node> new_node(new Node(to_insert)); n->m_children.push_back(new_node.get()); new_node.release(); which kind of clutters up what would have been a single line of code if I wasn't worrying about exception safety and a memory leak. (Actually I was wondering if I could post my whole code sample (about 300 lines) and ask people to critique it for idiomatic C++ usage in general, but I'm not sure whether that kind of question is appropriate on stackoverflow.)

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• Using a map with set_intersection

  - by Robin Welch

  Not used set_intersection before, but I believe it will work with maps. I wrote the following example code but it doesn't give me what I'd expect: #include <map> #include <string> #include <iostream> #include <algorithm> using namespace std; struct Money { double amount; string currency; bool operator< ( const Money& rhs ) const { if ( amount != rhs.amount ) return ( amount < rhs.amount ); return ( currency < rhs.currency ); } }; int main( int argc, char* argv[] ) { Money mn[] = { { 2.32, "USD" }, { 2.76, "USD" }, { 4.30, "GBP" }, { 1.21, "GBP" }, { 1.37, "GBP" }, { 6.74, "GBP" }, { 2.55, "EUR" } }; typedef pair< int, Money > MoneyPair; typedef map< int, Money > MoneyMap; MoneyMap map1; map1.insert( MoneyPair( 1, mn[1] ) ); map1.insert( MoneyPair( 2, mn[2] ) ); map1.insert( MoneyPair( 3, mn[3] ) ); // (3) map1.insert( MoneyPair( 4, mn[4] ) ); // (4) MoneyMap map2; map1.insert( MoneyPair( 3, mn[3] ) ); // (3) map1.insert( MoneyPair( 4, mn[4] ) ); // (4) map1.insert( MoneyPair( 5, mn[5] ) ); map1.insert( MoneyPair( 6, mn[6] ) ); map1.insert( MoneyPair( 7, mn[7] ) ); MoneyMap out; MoneyMap::iterator out_itr( out.begin() ); set_intersection( map1.begin(), map1.end(), map2.begin(), map2.end(), inserter( out, out_itr ) ); cout << "intersection has " << out.size() << " elements." << endl; return 0; } Since the pair labelled (3) and (4) appear in both maps, I was expecting that I'd get 2 elements in the intersection, but no, I get: intersection has 0 elements. I'm sure this is something to do with the comparitor on the map / pair but can't figure it out.

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• Catch Multiple Custom Exceptions? - C++

  - by Alex

  Hi all, I'm a student in my first C++ programming class, and I'm working on a project where we have to create multiple custom exception classes, and then in one of our event handlers, use a try/catch block to handle them appropriately. My question is: How do I catch my multiple custom exceptions in my try/catch block? GetMessage() is a custom method in my exception classes that returns the exception explanation as a std::string. Below I've included all the relevant code from my project. Thanks for your help! try/catch block // This is in one of my event handlers, newEnd is a wxTextCtrl try { first.ValidateData(); newEndT = first.ComputeEndTime(); *newEnd << newEndT; } catch (// don't know what do to here) { wxMessageBox(_(e.GetMessage()), _("Something Went Wrong!"), wxOK | wxICON_INFORMATION, this);; } ValidateData() Method void Time::ValidateData() { int startHours, startMins, endHours, endMins; startHours = startTime / MINUTES_TO_HOURS; startMins = startTime % MINUTES_TO_HOURS; endHours = endTime / MINUTES_TO_HOURS; endMins = endTime % MINUTES_TO_HOURS; if (!(startHours <= HOURS_MAX && startHours >= HOURS_MIN)) throw new HourOutOfRangeException("Beginning Time Hour Out of Range!"); if (!(endHours <= HOURS_MAX && endHours >= HOURS_MIN)) throw new HourOutOfRangeException("Ending Time Hour Out of Range!"); if (!(startMins <= MINUTE_MAX && startMins >= MINUTE_MIN)) throw new MinuteOutOfRangeException("Starting Time Minute Out of Range!"); if (!(endMins <= MINUTE_MAX && endMins >= MINUTE_MIN)) throw new MinuteOutOfRangeException("Ending Time Minute Out of Range!"); if(!(timeDifference <= P_MAX && timeDifference >= P_MIN)) throw new PercentageOutOfRangeException("Percentage Change Out of Range!"); if (!(startTime < endTime)) throw new StartEndException("Start Time Cannot Be Less Than End Time!"); } Just one of my custom exception classes, the others have the same structure as this one class HourOutOfRangeException { public: // param constructor // initializes message to passed paramater // preconditions - param will be a string // postconditions - message will be initialized // params a string // no return type HourOutOfRangeException(string pMessage) : message(pMessage) {} // GetMessage is getter for var message // params none // preconditions - none // postconditions - none // returns string string GetMessage() { return message; } // destructor ~HourOutOfRangeException() {} private: string message; };

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• gcc, strict-aliasing, and casting through a union

  - by Joseph Quinsey

  About a year ago the following paragraph was added to the GCC Manual, version 4.3.4, regarding -fstrict-aliasing: Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior [emphasis added], even if the cast uses a union type, e.g.: union a_union { int i; double d; }; int f() { double d = 3.0; return ((union a_union *)&d)->i; } Does anyone have an example to illustrate this undefined behavior? Note this question is not about what the C99 standard says, or does not say. It is about the actual functioning of gcc, and other existing compilers, today. My simple, naive, attempt fails. For example: #include <stdio.h> union a_union { int i; double d; }; int f1(void) { union a_union t; t.d = 3333333.0; return t.i; // gcc manual: 'type-punning is allowed, provided ...' } int f2(void) { double d = 3333333.0; return ((union a_union *)&d)->i; // gcc manual: 'undefined behavior' } int main(void) { printf("%d\n", f1()); printf("%d\n", f2()); return 0; } works fine, giving on CYGWIN: -2147483648 -2147483648 Also note that taking addresses is obviously wrong (or right, if you are trying to illustrate undefined behavior). For example, just as we know this is wrong: extern void foo(int *, double *); union a_union t; t.d = 3.0; foo(&t.i, &t.d); // UD behavior so is this wrong: extern void foo(int *, double *); double d = 3.0; foo(&((union a_union *)&d)->i, &d); // UD behavior For background discussion about this, see for example: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1422.pdf http://gcc.gnu.org/ml/gcc/2010-01/msg00013.html http://davmac.wordpress.com/2010/02/26/c99-revisited/ http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html http://stackoverflow.com/questions/98650/what-is-the-strict-aliasing-rule http://stackoverflow.com/questions/2771023/c99-strict-aliasing-rules-in-c-gcc/2771041#2771041 The first link, draft minutes of an ISO meeting seven months ago, notes in section 4.16: Is there anybody that thinks the rules are clear enough? No one is really able to interpret tham.

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• How can I create a Base64-Encoded string from an GDI+ Image in C++?

  - by Schnapple

  I asked a question recently, How can I create an Image in GDI+ from a Base64-Encoded string in C++?, which got a response that led me to the answer. Now I need to do the opposite - I have an Image in GDI+ whose image data I need to turn into a Base64-Encoded string. Due to its nature, it's not straightforward. The crux of the issue is that an Image in GDI+ can save out its data to either a file or an IStream*. I don't want to save to a file, so I need to use the resulting stream. Problem is, this is where my knowledge breaks down. This first part is what I figured out in the other question // Initialize GDI+. GdiplusStartupInput gdiplusStartupInput; ULONG_PTR gdiplusToken; GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL); // I have this decode function from elsewhere std::string decodedImage = base64_decode(Base64EncodedImage); // Allocate the space for the stream DWORD imageSize = decodedImage.length(); HGLOBAL hMem = ::GlobalAlloc(GMEM_MOVEABLE, imageSize); LPVOID pImage = ::GlobalLock(hMem); memcpy(pImage, decodedImage.c_str(), imageSize); // Create the stream IStream* pStream = NULL; ::CreateStreamOnHGlobal(hMem, FALSE, &pStream); // Create the image from the stream Image image(pStream); // Cleanup pStream->Release(); GlobalUnlock(hMem); GlobalFree(hMem); (Base64 code) And now I'm going to perform an operation on the resulting image, in this case rotating it, and now I want the Base64-equivalent string when I'm done. // Perform operation (rotate) image.RotateFlip(Gdiplus::Rotate180FlipNone); IStream* oStream = NULL; CLSID tiffClsid; GetEncoderClsid(L"image/tiff", &tiffClsid); // Function defined elsewhere image.Save(oStream, &tiffClsid); // And here's where I'm stumped. (GetEncoderClsid) So what I wind up with at the end is an IStream* object. But here's where both my knowledge and Google break down for me. IStream shouldn't be an object itself, it's an interface for other types of streams. I'd go down the road from getting string-Image in reverse, but I don't know how to determine the size of the stream, which appears to be key to that route. How can I go from an IStream* to a string (which I will then Base64-Encode)? Or is there a much better way to go from a GDI+ Image to a string?

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• Reading and writing C++ vector to a file

  - by JB

  For some graphics work I need to read in a large amount of data as quickly as possible and would ideally like to directly read and write the data structures to disk. Basically I have a load of 3d models in various file formats which take too long to load so I want to write them out in their "prepared" format as a cache that will load much faster on subsequent runs of the program. Is it safe to do it like this? My worries are around directly reading into the data of the vector? I've removed error checking, hard coded 4 as the size of the int and so on so that i can give a short working example, I know it's bad code, my question really is if it is safe in c++ to read a whole array of structures directly into a vector like this? I believe it to be so, but c++ has so many traps and undefined behavour when you start going low level and dealing directly with raw memory like this. I realise that number formats and sizes may change across platforms and compilers but this will only even be read and written by the same compiler program to cache data that may be needed on a later run of the same program. #include <fstream> #include <vector> using namespace std; struct Vertex { float x, y, z; }; typedef vector<Vertex> VertexList; int main() { // Create a list for testing VertexList list; Vertex v1 = {1.0f, 2.0f, 3.0f}; list.push_back(v1); Vertex v2 = {2.0f, 100.0f, 3.0f}; list.push_back(v2); Vertex v3 = {3.0f, 200.0f, 3.0f}; list.push_back(v3); Vertex v4 = {4.0f, 300.0f, 3.0f}; list.push_back(v4); // Write out a list to a disk file ofstream os ("data.dat", ios::binary); int size1 = list.size(); os.write((const char*)&size1, 4); os.write((const char*)&list[0], size1 * sizeof(Vertex)); os.close(); // Read it back in VertexList list2; ifstream is("data.dat", ios::binary); int size2; is.read((char*)&size2, 4); list2.resize(size2); // Is it safe to read a whole array of structures directly into the vector? is.read((char*)&list2[0], size2 * sizeof(Vertex)); }

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• C++ program Telephone Directory from a file

  - by Stacy Doyle

  I am writing a program for a phone directory. The user inputs a name and the program searches the file and either outputs the number or an error because the persons name is not in the file. The program should also ask the user if they would like to continue using the program and look up another number. So far runs and asks for the name and then prints the error message that I put in place saying that the name is not in the database. I am guessing that I must not really be having my program look in the file but not sure what to do also don't know how to get the program to run again if the user chooses to continue. #include <iostream> #include <fstream> #include <string> #include <iomanip> using namespace std; char chr; int main() { string first; string last; string number; string firstfile; string lastfile; string numberfile; int cont; ifstream infile; infile.open("name and numbers.dat"); //opening the file infile>>firstfile>>lastfile>>numberfile; cout<<"Enter a first and last name."<<endl; //Asking user for the input cin>>first>>last; //input the data { if(first==firstfile && last==lastfile) //if the entered information matches the information in the file cout<<first<<" "<<last<<"'s number is "<<numberfile<<endl; //this is printed else cout<<"Sorry that is not in our database."<<endl; //if the information doesn't match this is printed } cout<<"Would you like to search for another name? Y or N"<<endl; //user is asked if they would like to continue cin>>cont; infile.close(); //close file cin>>chr; return 0; }

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