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• Error in qsort function in Programming Pearls?

  - by Dervin Thunk

  Hello, is it just me or this code in Programming Pearls is wrong (quicksort wants 2 const voids, no?) If so, is my solution right? Apologies, just learning... int wordncmp(char *p, char* q) { int n = k; for ( ; *p == *q; p++, q++) if (*p == 0 && --n == 0) return 0; return *p - *q; } int sortcmp(char **p, char **q) { return wordncmp(*p, *q); } ... qsort(word, nword, sizeof(word[0]), sortcmp); Is this a solution? int sortcmp(const void *p, const void *q) { return wordncmp(* (char * const *) p, * (char * const *) q); }

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• Passing a template func. as a func. ptr to an overloaded func. - is there a way to compile this code

  - by LoudNPossiblyRight

  Just a general c++ curiosity: This code below shouldn't compile because it's impossible to know which to instantiate: temp(const int&) or temp(const string&) when calling func(temp) - this part i know. What i would like to know is if there is anything i can do to the line marked PASSINGLINE to get the compiler to deduce that i want FPTR1 called and not FPTR2 ? #include<iostream> using std::cout; using std::endl; /*FPTR1*/ void func(void(*fptr)(const int&)){ fptr(1001001);} /*FPTR2*/ void func(void(*fptr)(const string&)){ fptr("1001001"); } template <typename T> void temp(const T &t){ cout << t << endl; } int main(){ /*PASSINGLINE*/ func(temp); return 0; } Thank you.

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• How to make an ambiguous call distinct in C++?

  - by jcyang

  void outputString(const string &ss) { cout << "outputString(const string& ) " + ss << endl; } void outputString(const string ss) { cout << "outputString(const string ) " + ss << endl; } int main(void) { //! outputString("ambigiousmethod"); const string constStr = "ambigiousmethod2"; //! outputString(constStr); } ///:~ How to make distinct call? EDIT: This piece of code could be compiled with g++ and msvc. thanks.

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• C++ Passing `this` into method by reference

  - by David

  I have a class constructor that expects a reference to another class object to be passed in as an argument. I understand that references are preferable to pointers when no pointer arithmetic will be performed or when a null value will not exist. This is the header declaration of the constructor: class MixerLine { private: MIXERLINE _mixerLine; public: MixerLine(const MixerDevice& const parentMixer, DWORD destinationIndex); ~MixerLine(); } This is the code that calls the constructor (MixerDevice.cpp): void MixerDevice::enumerateLines() { DWORD numLines = getDestinationCount(); for(DWORD i=0;i<numLines;i++) { MixerLine mixerLine( this, i ); // other code here removed } } Compilation of MixerDevice.cpp fails with this error: Error 3 error C2664: 'MixerLine::MixerLine(const MixerDevice &,DWORD)' : cannot convert parameter 1 from 'MixerDevice *const ' to 'const MixerDevice &' But I thought pointer values could be assigned to pointers, e.g. Foo* foo = new Foo(); Foo& bar = foo;

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• Do I need multiple template specializations if I want to specialize for several kinds of strings?

  - by romkyns

  For example: template<typename T> void write(T value) { mystream << value; } template<> void write<const char*>(const char* value) { write_escaped(mystream, value); } template<> void write<char*>(char* value) { write_escaped(mystream, value); } template<> void write<std::string>(std::string value) { write_escaped(mystream.c_str(), value); } This looks like I'm doing it wrong, especially the two variants for const and non-const char*. However I checked that if I only specialize for const char * then passing a char * variable will invoke the non-specialized version, when called like this in VC++10: char something[25]; strcpy(something, "blah"); write(something); What would be the proper way of doing this?

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• Why can't we have an immutable version of operator[] for map

  - by Yan Cheng CHEOK

  The following code works fine : std::map<int, int>& m = std::map<int, int>(); int i = m[0]; But not the following code : // error C2678: binary '[' : no operator... const std::map<int, int>& m = std::map<int, int>(); int i = m[0]; Most of the time, I prefer to make most of my stuff to become immutable, due to reason : http://www.javapractices.com/topic/TopicAction.do?Id=29 I look at map source code. It has mapped_type& operator[](const key_type& _Keyval) Is there any reason, why std::map unable to provide const mapped_type& operator[](const key_type& _Keyval) const

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• C++ function object terminology functor, deltor, comparitor, etc..

  - by Robert S. Barnes

  Is there a commonly accepted terminology for various types for common functors? For instance I found myself naturally using comparitor for comparison functors like this: struct ciLessLibC : public std::binary_function<std::string, std::string, bool> { bool operator()(const std::string &lhs, const std::string &rhs) const { return strcasecmp(lhs.c_str(), rhs.c_str()) < 0 ? 1 : 0; } }; Or using the term deltor for something like this: struct DeleteAddrInfo { void operator()(const addr_map_t::value_type &pr) const { freeaddrinfo(pr.second); } }; If using these kinds of shorthand terms is common, it there some dictionary of them all someplace?

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• What is the best signature for overloaded arithmetic operators in C++?

  - by JohnMcG

  I had assumed that the canonical form for operator+, assuming the existence of an overloaded operator+= member function, was like this: const T operator+(const T& lhs, const T& rhs) { return T(lhs) +=rhs; } But it was pointed out to me that this would also work: const T operator+ (T lhs, const T& rhs) { return lhs+=rhs; } In essence, this form transfers creation of the temporary from the body of the implementation to the function call. It seems a little awkward to have different types for the two parameters, but is there anything wrong with the second form? Is there a reason to prefer one over the other?

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• Scheme - What is wrong with my attempt to extend this declaration?

  - by CppLearner

  This is a homework question. Question My attempt (the whole file): http://pastebin.com/vt3Q3dqs If you search let var = exp1 in body, that's the function I need to extend according to the question. When I test the sample code above, I get an error apply-env: No binding for y (eval "let x = 30 in let x = -(x,1) y = -(x,2) in -(x,y)") ; The following is execution log The-next-two-lines-shows-var-and-exp1 (x) (#(struct:const-exp 30)) diff-exp #(struct:var-exp x) #(struct:const-exp 1) diff-exp #(struct:var-exp x) #(struct:const-exp 2) The-next-two-lines-shows-var-and-exp1 (x y) (#(struct:diff-exp #(struct:var-exp x) #(struct:const-exp 1)) #(struct:diff-exp #(struct:var-exp x) #(struct:const-exp 2))) diff-exp #(struct:var-exp x) #(struct:var-exp y) As you can see, when the interperter reads the last line -(x,y) it complains because there is no binding. What did I do wrong? I know this is really long language, but if anyone can kindly lead me to the right direction would be really really nice. Thank you!

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• C++: How to make comparison function for char arrays?

  - by Newbie

  Is this possible? i get weird error message when i put char as the type: inline bool operator==(const char *str1, const char *str2){ // ... } Error message: error C2803: 'operator ==' must have at least one formal parameter of class type ... which i dont understand at all. I was thinking if i could directly compare stuff like: const char *str1 = "something"; const char *str2 = "something else"; const char str3[] = "lol"; // not sure if this is same as above and then compare: if(str1 == str2){ // ... } etc. But i also want it to work with: char *str = new char[100]; and: char *str = (char *)malloc(100); I am assuming every char array i use this way would end in NULL character, so the checking should be possible, but i understand it can be unsafe etc. I just want to know if this is possible to do, and how.

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• conversions in C++

  - by lego69

  I have this snippet of the code: header class A { private: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); ~A(); void foo() const; friend A& operator=(A& i, const A& member); }; operator= A& operator=(A& i, const A& member){ i(member.player); return i; } and I have row in my code: i = *pa1; A *pa1 = new A(a2); at the beginning i was int how can I fix it, thanks in advance I have an error must be non-static function

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• What C++ coding standard do you use?

  - by gablin

  For some time now, I've been unable to settle on a coding standard and use it concistently between projects. When starting a new project, I tend to change some things around (add a space there, remove a space there, add a line break there, an extra indent there, change naming conventions, etc.). So I figured that I might provide a piece of sample code, in C++, and ask you to rewrite it to fit your standard of coding. Inspiration is always good, I say. ^^ So here goes: #ifndef _DERIVED_CLASS_H__ #define _DERIVED_CLASS_H__ /** * This is an example file used for sampling code layout. * * @author Firstname Surname */ #include <stdio> #include <string> #include <list> #include "BaseClass.h" #include "Stuff.h" /** * The DerivedClass is completely useless. It represents uselessness in all its * entirety. */ class DerivedClass : public BaseClass { //////////////////////////////////////////////////////////// // CONSTRUCTORS / DESTRUCTORS //////////////////////////////////////////////////////////// public: /** * Constructs a useless object with default settings. * * @param value * Is never used. * @throws Exception * If something goes awry. */ DerivedClass (const int value) : uselessSize_ (0) {} /** * Constructs a copy of a given useless object. * * @param object * Object to copy. * @throws OutOfMemoryException * If necessary data cannot be allocated. */ ItemList (const DerivedClass& object) {} /** * Destroys this useless object. */ ~ItemList (); //////////////////////////////////////////////////////////// // PUBLIC METHODS //////////////////////////////////////////////////////////// public: /** * Clones a given useless object. * * @param object * Object to copy. * @return This useless object. */ DerivedClass& operator= (const DerivedClass& object) { stuff_ = object.stuff_; uselessSize_ = object.uselessSize_; } /** * Does absolutely nothing. * * @param useless * Pointer to useless data. */ void doNothing (const int* useless) { if (useless == NULL) { return; } else { int womba = *useless; switch (womba) { case 0: cout << "This is output 0"; break; case 1: cout << "This is output 1"; break; case 2: cout << "This is output 2"; break; default: cout << "This is default output"; break; } } } /** * Does even less. */ void doEvenLess () { int mySecret = getSecret (); int gather = 0; for (int i = 0; i < mySecret; i++) { gather += 2; } } //////////////////////////////////////////////////////////// // PRIVATE METHODS //////////////////////////////////////////////////////////// private: /** * Gets the secret value of this useless object. * * @return A secret value. */ int getSecret () const { if ((RANDOM == 42) && (stuff_.size() > 0) || (1000000000000000000 > 0) && true) { return 420; } else if (RANDOM == -1) { return ((5 * 2) + (4 - 1)) / 2; } int timer = 100; bool stopThisMadness = false; while (!stopThisMadness) { do { timer--; } while (timer > 0); stopThisMadness = true; } } //////////////////////////////////////////////////////////// // FIELDS //////////////////////////////////////////////////////////// private: /** * Don't know what this is used for. */ static const int RANDOM = 42; /** * List of lists of stuff. */ std::list <Stuff> stuff_; /** * Specifies the size of this object's uselessness. */ size_t uselessSize_; }; #endif

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• Is it bad practice to make an iterator that is aware of its own end

  - by aaronman

  For some background of why I am asking this question here is an example. In python the method chain chains an arbitrary number of ranges together and makes them into one without making copies. Here is a link in case you don't understand it. I decided I would implement chain in c++ using variadic templates. As far as I can tell the only way to make an iterator for chain that will successfully go to the next container is for each iterator to to know about the end of the container (I thought of a sort of hack in where when != is called against the end it will know to go to the next container, but the first way seemed easier and safer and more versatile). My question is if there is anything inherently wrong with an iterator knowing about its own end, my code is in c++ but this can be language agnostic since many languages have iterators. #ifndef CHAIN_HPP #define CHAIN_HPP #include "iterator_range.hpp" namespace iter { template <typename ... Containers> struct chain_iter; template <typename Container> struct chain_iter<Container> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end;//never really used but kept it for consistency public: chain_iter(Container & container, bool is_end=false) : begin(container.begin()),end(container.end()) { if(is_end) begin = container.end(); } chain_iter & operator++() { ++begin; return *this; } auto operator*()->decltype(*begin) { return *begin; } bool operator!=(const chain_iter & rhs) const{ return this->begin != rhs.begin; } }; template <typename Container, typename ... Containers> struct chain_iter<Container,Containers...> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end; bool end_reached = false; chain_iter<Containers...> next_iter; public: chain_iter(Container & container, Containers& ... rest, bool is_end=false) : begin(container.begin()), end(container.end()), next_iter(rest...,is_end) { if(is_end) begin = container.end(); } chain_iter & operator++() { if (begin == end) { ++next_iter; } else { ++begin; } return *this; } auto operator*()->decltype(*begin) { if (begin == end) { return *next_iter; } else { return *begin; } } bool operator !=(const chain_iter & rhs) const { if (begin == end) { return this->next_iter != rhs.next_iter; } else return this->begin != rhs.begin; } }; template <typename ... Containers> iterator_range<chain_iter<Containers...>> chain(Containers& ... containers) { auto begin = chain_iter<Containers...>(containers...); auto end = chain_iter<Containers...>(containers...,true); return iterator_range<chain_iter<Containers...>>(begin,end); } } #endif //CHAIN_HPP

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• C++ scoping error

  - by Pat Murray

  I have the following code: #include "Student.h" #include "SortedList.h" using namespace std; int main() { // points to the sorted list object SortedList *list = new SortedList; //This is line 17 // array to hold 100 student objects Student create[100]; int num = 100000; // holds different ID numbers // fills an array with 100 students of various ID numbers for (Student &x : create) { x = new Student(num); num += 100; } // insert all students into the sorted list for (Student &x : create) list->insert(&x); delete list; return 0; } And I keep getting the compile time error: main.cpp: In function ‘int main()’: main.cpp:17: error: ‘SortedList’ was not declared in this scope main.cpp:17: error: ‘list’ was not declared in this scope main.cpp:17: error: expected type-specifier before ‘SortedList’ main.cpp:17: error: expected `;' before ‘SortedList’ main.cpp:20: error: ‘Student’ was not declared in this scope main.cpp:20: error: expected primary-expression before ‘]’ token main.cpp:20: error: expected `;' before ‘create’ main.cpp:25: error: expected `;' before ‘x’ main.cpp:31: error: expected primary-expression before ‘for’ main.cpp:31: error: expected `;' before ‘for’ main.cpp:31: error: expected primary-expression before ‘for’ main.cpp:31: error: expected `)' before ‘for’ main.cpp:31: error: expected `;' before ‘x’ main.cpp:34: error: type ‘<type error>’ argument given to ‘delete’, expected pointer main.cpp:35: error: expected primary-expression before ‘return’ main.cpp:35: error: expected `)' before ‘return’ My Student.cpp and SortedList.cpp files compile just fine. They both also include .h files. I just do not understand why I get an error on that line. It seems to be a small issue though. Any insight would be appreciated. UPDATE1: I originally had .h files included, but i changed it when trying to figure out the cause of the error. The error remains with the .h files included though. UPDATE2: SortedList.h #ifndef SORTEDLIST_H #define SORTEDLIST_H #include "Student.h" /* * SortedList class * * A SortedList is an ordered collection of Students. The Students are ordered * from lowest numbered student ID to highest numbered student ID. */ class SortedList { public: SortedList(); // Constructs an empty list. SortedList(const SortedList & l); // Constructs a copy of the given student object ~SortedList(); // Destructs the sorted list object const SortedList & operator=(const SortedList & l); // Defines the assignment operator between two sorted list objects bool insert(Student *s); // If a student with the same ID is not already in the list, inserts // the given student into the list in the appropriate place and returns // true. If there is already a student in the list with the same ID // then the list is not changed and false is returned. Student *find(int studentID); // Searches the list for a student with the given student ID. If the // student is found, it is returned; if it is not found, NULL is returned. Student *remove(int studentID); // Searches the list for a student with the given student ID. If the // student is found, the student is removed from the list and returned; // if no student is found with the given ID, NULL is returned. // Note that the Student is NOT deleted - it is returned - however, // the removed list node should be deleted. void print() const; // Prints out the list of students to standard output. The students are // printed in order of student ID (from smallest to largest), one per line private: // Since Listnodes will only be used within the SortedList class, // we make it private. struct Listnode { Student *student; Listnode *next; }; Listnode *head; // pointer to first node in the list static void freeList(Listnode *L); // Traverses throught the linked list and deallocates each node static Listnode *copyList(Listnode *L); // Returns a pointer to the first node within a particular list }; #endif #ifndef STUDENT_H #define STUDENT_H Student.h #ifndef STUDENT_H #define STUDENT_H /* * Student class * * A Student object contains a student ID, the number of credits, and an * overall GPA. */ class Student { public: Student(); // Constructs a default student with an ID of 0, 0 credits, and 0.0 GPA. Student(int ID); // Constructs a student with the given ID, 0 credits, and 0.0 GPA. Student(int ID, int cr, double grPtAv); // Constructs a student with the given ID, number of credits, and GPA.\ Student(const Student & s); // Constructs a copy of another student object ~Student(); // Destructs a student object const Student & operator=(const Student & rhs); // Defines the assignment operator between two student objects // Accessors int getID() const; // returns the student ID int getCredits() const; // returns the number of credits double getGPA() const; // returns the GPA // Other methods void update(char grade, int cr); // Updates the total credits and overall GPA to take into account the // additions of the given letter grade in a course with the given number // of credits. The update is done by first converting the letter grade // into a numeric value (A = 4.0, B = 3.0, etc.). The new GPA is // calculated using the formula: // // (oldGPA * old_total_credits) + (numeric_grade * cr) // newGPA = --------------------------------------------------- // old_total_credits + cr // // Finally, the total credits is updated (to old_total_credits + cr) void print() const; // Prints out the student to standard output in the format: // ID,credits,GPA // Note: the end-of-line is NOT printed after the student information private: int studentID; int credits; double GPA; }; #endif

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• How do I implement AABB ray cast hit checking for opengl es on the iPhone

  - by Big Fizzy

  Basically, I draw a 3D cube, I can spin it around but I want to be able to touch it and know where on my cube's surface the user touched. I'm using for setting up, generating and spinning. Its based on the Molecules code and NeHe tutorial #5. Any help, links, tutorials and code would be greatly appreciated. I have lots of development experience but nothing much in the way of openGL and 3d. // // GLViewController.h // NeHe Lesson 05 // // Created by Jeff LaMarche on 12/12/08. // Copyright Jeff LaMarche Consulting 2008. All rights reserved. // #import "GLViewController.h" #import "GLView.h" @implementation GLViewController - (void)drawBox { static const GLfloat cubeVertices[] = { -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,-1.0f, 1.0f, -1.0f,-1.0f, 1.0f, -1.0f, 1.0f,-1.0f, 1.0f, 1.0f,-1.0f, 1.0f,-1.0f,-1.0f, -1.0f,-1.0f,-1.0f }; static const GLubyte cubeNumberOfIndices = 36; const GLubyte cubeVertexFaces[] = { 0, 1, 5, // Half of top face 0, 5, 4, // Other half of top face 4, 6, 5, // Half of front face 4, 6, 7, // Other half of front face 0, 1, 2, // Half of back face 0, 3, 2, // Other half of back face 1, 2, 5, // Half of right face 2, 5, 6, // Other half of right face 0, 3, 4, // Half of left face 7, 4, 3, // Other half of left face 3, 6, 2, // Half of bottom face 6, 7, 3, // Other half of bottom face }; const GLubyte cubeFaceColors[] = { 0, 255, 0, 255, 255, 125, 0, 255, 255, 0, 0, 255, 255, 255, 0, 255, 0, 0, 255, 255, 255, 0, 255, 255 }; glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer(3, GL_FLOAT, 0, cubeVertices); int colorIndex = 0; for(int i = 0; i < cubeNumberOfIndices; i += 3) { glColor4ub(cubeFaceColors[colorIndex], cubeFaceColors[colorIndex+1], cubeFaceColors[colorIndex+2], cubeFaceColors[colorIndex+3]); int face = (i / 3.0); if (face%2 != 0.0) colorIndex+=4; glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_BYTE, &cubeVertexFaces[i]); } glDisableClientState(GL_VERTEX_ARRAY); } //move this to a data model later! - (GLfixed)floatToFixed:(GLfloat)aValue; { return (GLfixed) (aValue * 65536.0f); } - (void)drawViewByRotatingAroundX:(float)xRotation rotatingAroundY:(float)yRotation scaling:(float)scaleFactor translationInX:(float)xTranslation translationInY:(float)yTranslation view:(GLView*)view; { glMatrixMode(GL_MODELVIEW); GLfixed currentModelViewMatrix[16] = { 45146, 47441, 2485, 0, -25149, 26775,-54274, 0, -40303, 36435, 36650, 0, 0, 0, 0, 65536 }; /* GLfixed currentModelViewMatrix[16] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 65536 }; */ //glLoadIdentity(); //glOrthof(-1.0f, 1.0f, -1.5f, 1.5f, -10.0f, 4.0f); // Reset rotation system if (isFirstDrawing) { //glLoadIdentity(); glMultMatrixx(currentModelViewMatrix); [self configureLighting]; isFirstDrawing = NO; } // Scale the view to fit current multitouch scaling GLfixed fixedPointScaleFactor = [self floatToFixed:scaleFactor]; glScalex(fixedPointScaleFactor, fixedPointScaleFactor, fixedPointScaleFactor); // Perform incremental rotation based on current angles in X and Y glGetFixedv(GL_MODELVIEW_MATRIX, currentModelViewMatrix); GLfloat totalRotation = sqrt(xRotation*xRotation + yRotation*yRotation); glRotatex([self floatToFixed:totalRotation], (GLfixed)((xRotation/totalRotation) * (GLfloat)currentModelViewMatrix[1] + (yRotation/totalRotation) * (GLfloat)currentModelViewMatrix[0]), (GLfixed)((xRotation/totalRotation) * (GLfloat)currentModelViewMatrix[5] + (yRotation/totalRotation) * (GLfloat)currentModelViewMatrix[4]), (GLfixed)((xRotation/totalRotation) * (GLfloat)currentModelViewMatrix[9] + (yRotation/totalRotation) * (GLfloat)currentModelViewMatrix[8]) ); // Translate the model by the accumulated amount glGetFixedv(GL_MODELVIEW_MATRIX, currentModelViewMatrix); float currentScaleFactor = sqrt(pow((GLfloat)currentModelViewMatrix[0] / 65536.0f, 2.0f) + pow((GLfloat)currentModelViewMatrix[1] / 65536.0f, 2.0f) + pow((GLfloat)currentModelViewMatrix[2] / 65536.0f, 2.0f)); xTranslation = xTranslation / (currentScaleFactor * currentScaleFactor); yTranslation = yTranslation / (currentScaleFactor * currentScaleFactor); // Grab the current model matrix, and use the (0,4,8) components to figure the eye's X axis in the model coordinate system, translate along that glTranslatef(xTranslation * (GLfloat)currentModelViewMatrix[0] / 65536.0f, xTranslation * (GLfloat)currentModelViewMatrix[4] / 65536.0f, xTranslation * (GLfloat)currentModelViewMatrix[8] / 65536.0f); // Grab the current model matrix, and use the (1,5,9) components to figure the eye's Y axis in the model coordinate system, translate along that glTranslatef(yTranslation * (GLfloat)currentModelViewMatrix[1] / 65536.0f, yTranslation * (GLfloat)currentModelViewMatrix[5] / 65536.0f, yTranslation * (GLfloat)currentModelViewMatrix[9] / 65536.0f); // Black background, with depth buffer enabled glClearColor(0.0f, 0.0f, 0.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); [self drawBox]; } - (void)configureLighting; { const GLfixed lightAmbient[] = {13107, 13107, 13107, 65535}; const GLfixed lightDiffuse[] = {65535, 65535, 65535, 65535}; const GLfixed matAmbient[] = {65535, 65535, 65535, 65535}; const GLfixed matDiffuse[] = {65535, 65535, 65535, 65535}; const GLfixed lightPosition[] = {30535, -30535, 0, 0}; const GLfixed lightShininess = 20; glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glEnable(GL_COLOR_MATERIAL); glMaterialxv(GL_FRONT_AND_BACK, GL_AMBIENT, matAmbient); glMaterialxv(GL_FRONT_AND_BACK, GL_DIFFUSE, matDiffuse); glMaterialx(GL_FRONT_AND_BACK, GL_SHININESS, lightShininess); glLightxv(GL_LIGHT0, GL_AMBIENT, lightAmbient); glLightxv(GL_LIGHT0, GL_DIFFUSE, lightDiffuse); glLightxv(GL_LIGHT0, GL_POSITION, lightPosition); glEnable(GL_DEPTH_TEST); glShadeModel(GL_SMOOTH); glEnable(GL_NORMALIZE); } -(void)setupView:(GLView*)view { const GLfloat zNear = 0.1, zFar = 1000.0, fieldOfView = 60.0; GLfloat size; glMatrixMode(GL_PROJECTION); glEnable(GL_DEPTH_TEST); size = zNear * tanf(DEGREES_TO_RADIANS(fieldOfView) / 2.0); CGRect rect = view.bounds; glFrustumf(-size, size, -size / (rect.size.width / rect.size.height), size / (rect.size.width / rect.size.height), zNear, zFar); glViewport(0, 0, rect.size.width, rect.size.height); glScissor(0, 0, rect.size.width, rect.size.height); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glClearColor(0.0f, 0.0f, 0.0f, 1.0f); glTranslatef(0.0f, 0.0f, -6.0f); isFirstDrawing = YES; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; } - (void)dealloc { [super dealloc]; } @end

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• Suggestions for duplicate file finder algorithm (using C)

  - by Andrei Ciobanu

  Hello, I wanted to write a program that test if two files are duplicates (have exactly the same content). First I test if the files have the same sizes, and if they have i start to compare their contents. My first idea, was to "split" the files into fixed size blocks, then start a thread for every block, fseek to startup character of every block and continue the comparisons in parallel. When a comparison from a thread fails, the other working threads are canceled, and the program exits out of the thread spawning loop. The code looks like this: dupf.h #ifndef __NM__DUPF__H__ #define __NM__DUPF__H__ #define NUM_THREADS 15 #define BLOCK_SIZE 8192 /* Thread argument structure */ struct thread_arg_s { const char *name_f1; /* First file name */ const char *name_f2; /* Second file name */ int cursor; /* Where to seek in the file */ }; typedef struct thread_arg_s thread_arg; /** * 'arg' is of type thread_arg. * Checks if the specified file blocks are * duplicates. */ void *check_block_dup(void *arg); /** * Checks if two files are duplicates */ int check_dup(const char *name_f1, const char *name_f2); /** * Returns a valid pointer to a file. * If the file (given by the path/name 'fname') cannot be opened * in 'mode', the program is interrupted an error message is shown. **/ FILE *safe_fopen(const char *name, const char *mode); #endif dupf.c #include <errno.h> #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <unistd.h> #include "dupf.h" FILE *safe_fopen(const char *fname, const char *mode) { FILE *f = NULL; f = fopen(fname, mode); if (f == NULL) { char emsg[255]; sprintf(emsg, "FOPEN() %s\t", fname); perror(emsg); exit(-1); } return (f); } void *check_block_dup(void *arg) { const char *name_f1 = NULL, *name_f2 = NULL; /* File names */ FILE *f1 = NULL, *f2 = NULL; /* Streams */ int cursor = 0; /* Reading cursor */ char buff_f1[BLOCK_SIZE], buff_f2[BLOCK_SIZE]; /* Character buffers */ int rchars_1, rchars_2; /* Readed characters */ /* Initializing variables from 'arg' */ name_f1 = ((thread_arg*)arg)->name_f1; name_f2 = ((thread_arg*)arg)->name_f2; cursor = ((thread_arg*)arg)->cursor; /* Opening files */ f1 = safe_fopen(name_f1, "r"); f2 = safe_fopen(name_f2, "r"); /* Setup cursor in files */ fseek(f1, cursor, SEEK_SET); fseek(f2, cursor, SEEK_SET); /* Initialize buffers */ rchars_1 = fread(buff_f1, 1, BLOCK_SIZE, f1); rchars_2 = fread(buff_f2, 1, BLOCK_SIZE, f2); if (rchars_1 != rchars_2) { /* fread failed to read the same portion. * program cannot continue */ perror("ERROR WHEN READING BLOCK"); exit(-1); } while (rchars_1-->0) { if (buff_f1[rchars_1] != buff_f2[rchars_1]) { /* Different characters */ fclose(f1); fclose(f2); pthread_exit("notdup"); } } /* Close streams */ fclose(f1); fclose(f2); pthread_exit("dup"); } int check_dup(const char *name_f1, const char *name_f2) { int num_blocks = 0; /* Number of 'blocks' to check */ int num_tsp = 0; /* Number of threads spawns */ int tsp_iter = 0; /* Iterator for threads spawns */ pthread_t *tsp_threads = NULL; thread_arg *tsp_threads_args = NULL; int tsp_threads_iter = 0; int thread_c_res = 0; /* Thread creation result */ int thread_j_res = 0; /* Thread join res */ int loop_res = 0; /* Function result */ int cursor; struct stat buf_f1; struct stat buf_f2; if (name_f1 == NULL || name_f2 == NULL) { /* Invalid input parameters */ perror("INVALID FNAMES\t"); return (-1); } if (stat(name_f1, &buf_f1) != 0 || stat(name_f2, &buf_f2) != 0) { /* Stat fails */ char emsg[255]; sprintf(emsg, "STAT() ERROR: %s %s\t", name_f1, name_f2); perror(emsg); return (-1); } if (buf_f1.st_size != buf_f2.st_size) { /* File have different sizes */ return (1); } /* Files have the same size, function exec. is continued */ num_blocks = (buf_f1.st_size / BLOCK_SIZE) + 1; num_tsp = (num_blocks / NUM_THREADS) + 1; cursor = 0; for (tsp_iter = 0; tsp_iter < num_tsp; tsp_iter++) { loop_res = 0; /* Create threads array for this spawn */ tsp_threads = malloc(NUM_THREADS * sizeof(*tsp_threads)); if (tsp_threads == NULL) { perror("TSP_THREADS ALLOC FAILURE\t"); return (-1); } /* Create arguments for every thread in the current spawn */ tsp_threads_args = malloc(NUM_THREADS * sizeof(*tsp_threads_args)); if (tsp_threads_args == NULL) { perror("TSP THREADS ARGS ALLOCA FAILURE\t"); return (-1); } /* Initialize arguments and create threads */ for (tsp_threads_iter = 0; tsp_threads_iter < NUM_THREADS; tsp_threads_iter++) { if (cursor >= buf_f1.st_size) { break; } tsp_threads_args[tsp_threads_iter].name_f1 = name_f1; tsp_threads_args[tsp_threads_iter].name_f2 = name_f2; tsp_threads_args[tsp_threads_iter].cursor = cursor; thread_c_res = pthread_create( &tsp_threads[tsp_threads_iter], NULL, check_block_dup, (void*)&tsp_threads_args[tsp_threads_iter]); if (thread_c_res != 0) { perror("THREAD CREATION FAILURE"); return (-1); } cursor+=BLOCK_SIZE; } /* Join last threads and get their status */ while (tsp_threads_iter-->0) { void *thread_res = NULL; thread_j_res = pthread_join(tsp_threads[tsp_threads_iter], &thread_res); if (thread_j_res != 0) { perror("THREAD JOIN FAILURE"); return (-1); } if (strcmp((char*)thread_res, "notdup")==0) { loop_res++; /* Closing other threads and exiting by condition * from loop. */ while (tsp_threads_iter-->0) { pthread_cancel(tsp_threads[tsp_threads_iter]); } } } free(tsp_threads); free(tsp_threads_args); if (loop_res > 0) { break; } } return (loop_res > 0) ? 1 : 0; } The function works fine (at least for what I've tested). Still, some guys from #C (freenode) suggested that the solution is overly complicated, and it may perform poorly because of parallel reading on hddisk. What I want to know: Is the threaded approach flawed by default ? Is fseek() so slow ? Is there a way to somehow map the files to memory and then compare them ?

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• OO Design - polymorphism - how to design for handing streams of different file types

  - by Kache4

  I've little experience with advanced OO practices, and I want to design this properly as an exercise. I'm thinking of implementing the following, and I'm asking if I'm going about this the right way. I have a class PImage that holds the raw data and some information I need for an image file. Its header is currently something like this: #include <boost/filesytem.hpp> #include <vector> namespace fs = boost::filesystem; class PImage { public: PImage(const fs::path& path, const unsigned char* buffer, int bufferLen); const vector<char> data() const { return data_; } const char* rawData() const { return &data_[0]; } /*** other assorted accessors ***/ private: fs::path path_; int width_; int height_; int filesize_; vector<char> data_; } I want to fill the width_ and height_ by looking through the file's header. The trivial/inelegant solution would be to have a lot of messy control flow that identifies the type of image file (.gif, .jpg, .png, etc) and then parse the header accordingly. Instead of using vector<char> data_, I was thinking of having PImage use a class, RawImageStream data_ that inherits from vector<char>. Each type of file I plan to support would then inherit from RawImageStream, e.g. RawGifStream, RawPngStream. Each RawXYZStream would encapsulate the respective header-parsing functions, and PImage would only have to do something like height_ = data_.getHeight();. Am I thinking this through correctly? How would I create the proper RawImageStream subclass for data_ to be in the PImage ctor? Is this where I could use an object factory? Anything I'm forgetting?

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• qsort on an array of pointers to Objective-C objects

  - by ElBueno

  I have an array of pointers to Objective-C objects. These objects have a sort key associated with them. I'm trying to use qsort to sort the array of pointers to these objects. However, the first time my comparator is called, the first argument points to the first element in my array, but the second argument points to garbage, giving me an EXC_BAD_ACCESS when I try to access its sort key. Here is my code (paraphrased): - (void)foo:(int)numThingies { Thingie **array; array = malloc(sizeof(deck[0])*numThingies); for(int i = 0; i < numThingies; i++) { array[i] = [[Thingie alloc] initWithSortKey:(float)random()/RAND_MAX]; } qsort(array[0], numThingies, sizeof(array[0]), thingieCmp); } int thingieCmp(const void *a, const void *b) { const Thingie *ia = (const Thingie *)a; const Thingie *ib = (const Thingie *)b; if (ia.sortKey > ib.sortKey) return 1; //ib point to garbage, so ib.sortKey produces the EXC_BAD_ACCESS else return -1; } Any ideas why this is happening?

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• EXC_BREAKPOINT when starting iPhone app

  - by pgb

  A user of our app sent me the following crash log: Incident Identifier: 59D4D5E7-570A-4047-A679-3016B2A226C4 CrashReporter Key: d8284d671ee22ad17511360ce73409ebfa8b84bb Process: .... [63] Path: /var/mobile/Applications/.... Identifier: ... Version: ??? (???) Code Type: ARM (Native) Parent Process: launchd [1] Date/Time: 2010-03-08 17:00:15.437 -0800 OS Version: iPhone OS 2.2.1 (5H11a) Report Version: 103 Exception Type: EXC_BREAKPOINT (SIGTRAP) Exception Codes: 0x00000001, 0xe7ffdefe Crashed Thread: 0 Thread 0 Crashed: 0 dyld 0x2fe01060 dyld_fatal_error + 0 1 dyld 0x2fe088d4 dyld::_main(mach_header const*, unsigned long, int, char const**, char const**, char const**) + 3064 2 dyld 0x2fe0196c dyldbootstrap::start(mach_header const*, int, char const**, long) + 884 3 dyld 0x2fe01048 _dyld_start + 32 Thread 0 crashed with ARM Thread State: r0: 0x2fe23ca0 r1: 0x00000000 r2: 0x2fe23ca0 r3: 0x00000000 r4: 0x2ffff4e0 r5: 0x2ffff4bc r6: 0x2fe005c0 r7: 0x2ffffb00 r8: 0x00000004 r9: 0x2fe57cf0 r10: 0x2fe236c8 r11: 0x00000009 ip: 0x0000018d sp: 0x2ffff5b8 lr: 0x2fe088dc pc: 0x2fe01060 cpsr: 0x00000010 Binary Images: 0x2fe00000 - 0x2fe22fff dyld ??? (???) <f6a50d5f57a676b54276d0ecef46d5f0> /usr/lib/dyld My app uses OpenFeint and PinchMedia analytics. For PinchMedia, I'm linking using their provided .a file, and for OpenFeint, I'm compiling their code (as per their guidelines). The frameworks / libs I'm linking are: UIKit.framework (Weak) MapKit.framework (Weak) Foundation.framework CoreGraphics.framework OpenAL.framework AudioToolbox.framework libsqlite3 SystemConfiguration.framework CoreLocation.framework PinchMedia analytics Security.framework QuartzCore.framework CFNetwork.framework My base SDK is iPhone 3.0, and my Base OS Deployment Target is 2.2.1. There are two things I find weird: The app crashes even before the main method is invoked. The crash log looks exactly like the one posted here: http://stackoverflow.com/questions/2368689/objective-c-iphone-app-exc-breakpoint-sigtrap The user that sent me this crash is using a 2nd gen iPod Touch with OS 2.2.1. I wasn't able to reproduce the issue, but based on the comments in iTunes, it seems that more people is having the same issue.

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• Help with Boost Spirit ASTs

  - by Decmac04

  I am writing a small tool for analyzing simple B Machine substitutions as part of a college research work. The code successfully parse test inputs of the form mySubst := var1 + var2. However, I get a pop-up error message saying "This application has requested the Runtime to terminate it in an unusual way. " In the command prompt window, I get an "Assertion failed message". The main program is given below: // BMachineTree.cpp : Defines the entry point for the console application. // /*============================================================================= Copyright (c) 2010 Temitope Onunkun =============================================================================*/ /////////////////////////////////////////////////////////////////////////////// // // UUsing Boost Spririt Trees (AST) to parse B Machine Substitutions. // /////////////////////////////////////////////////////////////////////////////// #define BOOST_SPIRIT_DUMP_PARSETREE_AS_XML #include <boost/spirit/core.hpp> #include <boost/spirit/tree/ast.hpp> #include <boost/spirit/tree/tree_to_xml.hpp> #include "BMachineTreeGrammar.hpp" #include <iostream> #include <stack> #include <functional> #include <string> #include <cassert> #include <vector> #if defined(BOOST_SPIRIT_DUMP_PARSETREE_AS_XML) #include <map> #endif // Using AST to parse B Machine substitutions //////////////////////////////////////////////////////////////////////////// using namespace std; using namespace boost::spirit; typedef char const* iterator_t; typedef tree_match<iterator_t> parse_tree_match_t; typedef parse_tree_match_t::tree_iterator iter_t; //////////////////////////////////////////////////////////////////////////// string evaluate(parse_tree_match_t hit); string eval_machine(iter_t const& i); vector<string> dx; string evaluate(tree_parse_info<> info) { return eval_machine(info.trees.begin()); } string eval_machine(iter_t const& i) { cout << "In eval_machine. i->value = " << string(i->value.begin(), i->value.end()) << " i->children.size() = " << i->children.size() << endl; if (i->value.id() == substitution::leafValueID) { assert(i->children.size() == 0); // extract string tokens string leafValue(i->value.begin(), i->value.end()); dx.push_back(leafValue.c_str()); return leafValue.c_str(); } // else if (i->value.id() == substitution::termID) { if ( (*i->value.begin() == '*') || (*i->value.begin() == '/') ) { assert(i->children.size() == 2); dx.push_back( eval_machine(i->children.begin()) ); dx.push_back( eval_machine(i->children.begin()+1) ); return eval_machine(i->children.begin()) + " " + eval_machine(i->children.begin()+1); } // else assert(0); } else if (i->value.id() == substitution::expressionID) { if ( (*i->value.begin() == '+') || (*i->value.begin() == '-') ) { assert(i->children.size() == 2); dx.push_back( eval_machine(i->children.begin()) ); dx.push_back( eval_machine(i->children.begin()+1) ); return eval_machine(i->children.begin()) + " " + eval_machine(i->children.begin()+1); } else assert(0); } // else if (i->value.id() == substitution::simple_substID) { if (*i->value.begin() == (':' >> '=') ) { assert(i->children.size() == 2); dx.push_back( eval_machine(i->children.begin()) ); dx.push_back( eval_machine(i->children.begin()+1) ); return eval_machine(i->children.begin()) + "|->" + eval_machine(i->children.begin()+1); } else assert(0); } else { assert(0); // error } return 0; } //////////////////////////////////////////////////////////////////////////// int main() { // look in BMachineTreeGrammar for the definition of BMachine substitution BMach_subst; cout << "/////////////////////////////////////////////////////////\n\n"; cout << "\t\tB Machine Substitution...\n\n"; cout << "/////////////////////////////////////////////////////////\n\n"; cout << "Type an expression...or [q or Q] to quit\n\n"; string str; while (getline(cin, str)) { if (str.empty() || str[0] == 'q' || str[0] == 'Q') break; tree_parse_info<> info = ast_parse(str.c_str(), BMach_subst, space_p); if (info.full) { #if defined(BOOST_SPIRIT_DUMP_PARSETREE_AS_XML) // dump parse tree as XML std::map<parser_id, std::string> rule_names; rule_names[substitution::identifierID] = "identifier"; rule_names[substitution::leafValueID] = "leafValue"; rule_names[substitution::factorID] = "factor"; rule_names[substitution::termID] = "term"; rule_names[substitution::expressionID] = "expression"; rule_names[substitution::simple_substID] = "simple_subst"; tree_to_xml(cout, info.trees, str.c_str(), rule_names); #endif // print the result cout << "Variables in Vector dx: " << endl; for(vector<string>::iterator idx = dx.begin(); idx < dx.end(); ++idx) cout << *idx << endl; cout << "parsing succeeded\n"; cout << "result = " << evaluate(info) << "\n\n"; } else { cout << "parsing failed\n"; } } cout << "Bye... :-) \n\n"; return 0; } The grammar, defined in BMachineTreeGrammar.hpp file is given below: /*============================================================================= Copyright (c) 2010 Temitope Onunkun http://www.dcs.kcl.ac.uk/pg/onun Use, modification and distribution is subject to the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) =============================================================================*/ #ifndef BOOST_SPIRIT_BMachineTreeGrammar_HPP_ #define BOOST_SPIRIT_BMachineTreeGrammar_HPP_ using namespace boost::spirit; /////////////////////////////////////////////////////////////////////////////// // // Using Boost Spririt Trees (AST) to parse B Machine Substitutions. // /////////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// // // B Machine Grammar // //////////////////////////////////////////////////////////////////////////// struct substitution : public grammar<substitution> { static const int identifierID = 1; static const int leafValueID = 2; static const int factorID = 3; static const int termID = 4; static const int expressionID = 5; static const int simple_substID = 6; template <typename ScannerT> struct definition { definition(substitution const& ) { // Start grammar definition identifier = alpha_p >> (+alnum_p | ch_p('_') ) ; leafValue = leaf_node_d[ lexeme_d[ identifier | +digit_p ] ] ; factor = leafValue | inner_node_d[ ch_p( '(' ) >> expression >> ch_p(')' ) ] ; term = factor >> *( (root_node_d[ch_p('*') ] >> factor ) | (root_node_d[ch_p('/') ] >> factor ) ); expression = term >> *( (root_node_d[ch_p('+') ] >> term ) | (root_node_d[ch_p('-') ] >> term ) ); simple_subst= leaf_node_d[ lexeme_d[ identifier ] ] >> root_node_d[str_p(":=")] >> expression ; // End grammar definition // turn on the debugging info. BOOST_SPIRIT_DEBUG_RULE(identifier); BOOST_SPIRIT_DEBUG_RULE(leafValue); BOOST_SPIRIT_DEBUG_RULE(factor); BOOST_SPIRIT_DEBUG_RULE(term); BOOST_SPIRIT_DEBUG_RULE(expression); BOOST_SPIRIT_DEBUG_RULE(simple_subst); } rule<ScannerT, parser_context<>, parser_tag<simple_substID> > simple_subst; rule<ScannerT, parser_context<>, parser_tag<expressionID> > expression; rule<ScannerT, parser_context<>, parser_tag<termID> > term; rule<ScannerT, parser_context<>, parser_tag<factorID> > factor; rule<ScannerT, parser_context<>, parser_tag<leafValueID> > leafValue; rule<ScannerT, parser_context<>, parser_tag<identifierID> > identifier; rule<ScannerT, parser_context<>, parser_tag<simple_substID> > const& start() const { return simple_subst; } }; }; #endif The output I get on running the program is: ///////////////////////////////////////////////////////// B Machine Substitution... ///////////////////////////////////////////////////////// Type an expression...or [q or Q] to quit mySubst := var1 - var2 parsing succeeded In eval_machine. i->value = := i->children.size() = 2 Assertion failed: 0, file c:\redmound\bmachinetree\bmachinetree\bmachinetree.cpp , line 114 I will appreciate any help in resolving this problem.

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• correct fisheye distortion

  - by Will

  I have some points that describe positions in a picture taken with a fisheye lens. I've found this description of how to generate a fisheye effect, but not how to reverse it. How do you calculate the radial distance from the centre to go from fisheye to rectilinear? My function stub looks like this: Point correct_fisheye(const Point& p,const Size& img) { // to polar const Point centre = {img.width/2,img.height/2}; const Point rel = {p.x-centre.x,p.y-centre.y}; const double theta = atan2(rel.y,rel.x); double R = sqrt((rel.x*rel.x)+(rel.y*rel.y)); // fisheye undistortion in here please //... change R ... // back to rectangular const Point ret = Point(centre.x+R*cos(theta),centre.y+R*sin(theta)); fprintf(stderr,"(%d,%d) in (%d,%d) = %f,%f = (%d,%d)\n",p.x,p.y,img.width,img.height,theta,R,ret.x,ret.y); return ret; }

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• Reference-type conversion operators: asking for trouble?

  - by Ben

  When I compile the following code using g++ class A {}; void foo(A&) {} int main() { foo(A()); return 0; } I get the following error messages: > g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:10: error: invalid initialization of non-const reference of type ‘A&’ from a temporary of type ‘A’ test.cpp:6: error: in passing argument 1 of ‘void foo(A&)’ After some reflection, these errors make plenty of sense to me. A() is just a temporary value, not an assignable location on the stack, so it wouldn't seem to have an address. If it doesn't have an address, then I can't hold a reference to it. Okay, fine. But wait! If I add the following conversion operator to the class A class A { public: operator A&() { return *this; } }; then all is well! My question is whether this even remotely safe. What exactly does this point to when A() is constructed as a temporary value? I am given some confidence by the fact that void foo(const A&) {} can accept temporary values according to g++ and all other compilers I've used. The const keyword can always be cast away, so it would surprise me if there were any actual semantic differences between a const A& parameter and an A& parameter. So I guess that's another way of asking my question: why is a const reference to a temporary value considered safe by the compiler whereas a non-const reference is not?

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• Declaring functors for comparison ??

  - by Mr.Gando

  Hello, I have seen other people questions but found none that applied to what I'm trying to achieve here. I'm trying to sort Entities via my EntityManager class using std::sort and a std::vector<Entity *> /*Entity.h*/ class Entity { public: float x,y; }; struct compareByX{ bool operator()(const GameEntity &a, const GameEntity &b) { return (a.x < b.x); } }; /*Class EntityManager that uses Entitiy*/ typedef std::vector<Entity *> ENTITY_VECTOR; //Entity reference vector class EntityManager: public Entity { private: ENTITY_VECTOR managedEntities; public: void sortEntitiesX(); }; void EntityManager::sortEntitiesX() { /*perform sorting of the entitiesList by their X value*/ compareByX comparer; std::sort(entityList.begin(), entityList.end(), comparer); } I'm getting a dozen of errors like : error: no match for call to '(compareByX) (GameEntity* const&, GameEntity* const&)' : note: candidates are: bool compareByX::operator()(const GameEntity&, const GameEntity&) I'm not sure but ENTITY_VECTOR is std::vector<Entity *> , and I don't know if that could be the problem when using the compareByX functor ? I'm pretty new to C++, so any kind of help is welcome.

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• Why does this cast to Base class in virtual function give a segmentation fault?

  - by dehmann

  I want to print out a derived class using the operator<<. When I print the derived class, I want to first print its base and then its own content. But I ran into some trouble (see segfault below): class Base { public: friend std::ostream& operator<<(std::ostream&, const Base&); virtual void Print(std::ostream& out) const { out << "BASE!"; } }; std::ostream& operator<<(std::ostream& out, const Base& b) { b.Print(out); return out; } class Derived : public Base { public: virtual void Print(std::ostream& out) const { out << "My base: "; //((const Base*)this)->Print(out); // infinite, calls this fct recursively //((Base*)this)->Print(out); // segfault (from infinite loop?) ((Base)*this).Print(out); // OK out << " ... and myself."; } }; int main(int argc, char** argv){ Derived d; std::cout << d; return 0; } Why can't I cast in one of these ways? ((const Base*)this)->Print(out); // infinite, calls this fct recursively ((Base*)this)->Print(out); // segfault (from infinite loop?)

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• Linking the Linker script file to source code

  - by user304097

  Hello , I am new to GNU compiler. I have a C source code file which contains some structures and variables in which I need to place certain variables at a particular locations. So, I have written a linker script file and used the __ attribute__("SECTION") at variable declaration, in C source code. I am using a GNU compiler (cygwin) to compile the source code and creating a .hex file using -objcopy option, but I am not getting how to link my linker script file at compilation to relocate the variables accordingly. I am attaching the linker script file and the C source file for the reference. Please help me link the linker script file to my source code, while creating the .hex file using GNU. /*linker script file*/ /*defining memory regions*/ MEMORY { base_table_ram : org = 0x00700000, len = 0x00000100 /*base table area for BASE table*/ mem2 : org =0x00800200, len = 0x00000300 /* other structure variables*/ } /*Sections directive definitions*/ SECTIONS { BASE_TABLE : { } > base_table_ram GROUP : { .text : { } { *(SEG_HEADER) } .data : { } { *(SEG_HEADER) } .bss : { } { *(SEG_HEADER) } } > mem2 } C source code: const UINT8 un8_Offset_1 __attribute__((section("BASE_TABLE"))) = 0x1A; const UINT8 un8_Offset_2 __attribute__((section("BASE_TABLE"))) = 0x2A; const UINT8 un8_Offset_3 __attribute__((section("BASE_TABLE"))) = 0x3A; const UINT8 un8_Offset_4 __attribute__((section("BASE_TABLE"))) = 0x4A; const UINT8 un8_Offset_5 __attribute__((section("BASE_TABLE"))) = 0x5A; const UINT8 un8_Offset_6 __attribute__((section("SEG_HEADER"))) = 0x6A; My intention is to place the variables of section "BASE_TABLE" at the address defined i the linker script file and the remaining variables at the "SEG_HEADER" defined in the linker script file above. But after compilation when I look in to the .hex file the different section variables are located in different hex records, located at an address of 0x00, not the one given in linker script file . Please help me in linking the linker script file to source code. Are there any command line options to link the linker script file, if any plese provide me with the info how to use the options. Thanks in advance, SureshDN.

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