What I need to know is how I can pass an argument to the Book constructor so I can change the const data member Category (with cascading capacity if possible. I also posted some of my set functions for further comprehension.
class Book
{
friend void CompPrice(Book &,Book&); //friend function that has access to the member functions of this class
//The arguments sent to it are by address, and of type the class Book, so that it can have access to its member functions
private: //private data members
I have a class that defines a window (a popup dialog of sorts), and I want the name of that window to be constant. The only problem is that the name of the popup needs to match the title of the parent window, and I get the name of the parent in the constructor. So how do I go about defining this member variable to be constant and initializing it with a value in the constructor?
I want to do something like this, but I know this isn't allowed:
/* class.h */ class foo { public: foo(*parentWindowPtr);
[Code] .....
I should mention that yes the name of the parent window is const char *, and I would like to keep it this way.
The problem with that is that string.data isn't considered const during the initialization of the String struct so the compiler throws an error. It doesn't feel very elegant to do it like this either way.
Is there an elegant solution to this problem? I would like to avoid making a copy of the string literal.
The problem occurs in here, I get access violations, is there a way to this while keeping Display const or is this code valid and my problem is somewhere else and not being caught in the debugger? I tried to make the return types const - but that didn't work .....
//Getters need const twice for this to work? const char* Player::GetName() const {return m_name;} const int Player::GetGrade() const {return m_grade;} const double Player::GetGPA() const {return m_gpa;}
i am trying to describe the unusual situation where you declare a class member function with this format:
bool class::function_name(void) const
Specifically where the 'const' follows the parameter list. It is my understanding this is a very useful way of ensuring that whatever code you put in the function definition cannot change any data members of its class.
However I have recently read that this form of declaration should not be used as it leads to less optimized and slower code. Is this correct?
When I try to compile functionB in Visual C++ it gives me this error:-
glibmm/refptr.h(199) : error C2440: 'initializing' : cannot convert from 'const Gdk::Window *' to 'Gdk::Window *' Conversion loses qualifiers
And this is the code from glibmm/refptr.h
Code: // The templated ctor allows copy construction from any object that's castable. Thus, it does downcasts: // base_ref = derived_ref template <class T_CppObject> template <class T_CastFrom>
[Code] .....
I don't actually want to change anything in the member variable canvas_event_box. I just want to be able to call one of its functions from my 'const' member function. Is there any syntax I can use to tell VC++ that I'm not actually changing the variable - just using it.
enum Country {India, China, France, NumCountries}; // plus many other countries struct School {}; struct Mall {}; struct HockeyArena {};
[Code] ....
Output:
PersonFactory::initializeEthnicNames() called Carrying out the initialization... PersonFactory::initializeEthnicNames() called PersonFactory::initializeEthnicNames() called PersonFactory::initializeEthnicNames() called PersonFactory::initializeEthnicNames() called numberOfTimesInitialized = 1
As you can see, even though five PersonFactory objects were constructed, the ethnicNames initialization only occurred once, as desired. However, there are some issues with my method. First of all, the use of the comma operator is ugly in my opinion. But fashion statements aside, PersonFactory::initializeEthnicNames() is still called multiple times, which is not good, even though it correctly avoids reinitializing ethnicNames after the first call. Also, I now forever get the annoying compiler warnings that the bool namesInitialized is never used, which is true, thus wasting a small bit of memory. And finally, I cannot declare ethnicNames const now, and it is supposed to be const. Any better way to accomplish what I'm trying to do?
By the way, the reason why I don't initialize ethnic names outside the class as is normally done for static data members (and that would indeed allow me to declare it const) is because it would get messed up if I later change the order of the elements in enum Country. Hence actual lines of initializations I think are needed. And I do want ethnicSurnames inside PersonFactory, because I feel it really does belong there. Also, PersonFactory is not to be Singleton, because it has data members that depend on some parameters in its constructor (e.g. geographic location).
This does not allow me to initialize _listRef as something like NULL when it is not applicable.Also, i must change all my constructors and its child class to include an initialization of _listRef!!
What is the alternative? Is pointer the nearest? which of the following should be used?
Code: const QList<QSharedPointer<Data>> * _listRef; or const QList<QSharedPointer<Data>> *const _listRef; or const QSharedPointer<QList<QSharedPointer<Data>>> _listRef; ????
Are there other ways of calling a const/non-const override? I want to defined some functions in terms of others, particularly accessors which might or might not require constness- in order to not copy & paste code. This is my current solution:
difference between const and static const, more effectively. I know the basic concept of const and static but I need clear explanation of declaring "const" and "static const"
Is there any way to cast a non-const variable to const one?
I want to read variable n from file and then use it to declare array "int arr[n]", but because n is non-const, the compiler doesn't allow me to do that.
I am getting this error invalid use of non static data member.my code looks something like this: i have a main.cpp and 2 class files with respective .h files, say one class file is named human (so i have human.cpp and human.h) and stats (so i have stats.cpp and stats.h) in my stats.h file, i have a double array: double HumanF[10][12] with everything filled in.then in my human.h file i just have a bunch of integers. human.cpp has formulas in it that use numbers from the double array i mentioned. for example
Human::Human() { constant (this is a double i made in human.h) = (1+Stats::HumanF[0][0]); i (another double) = pow(constant, ylvl); (ylvl is also an int I made in my header file) yhp = i*137; }
Here's a part of my program. What I need to know is how I can pass an argument to the Book constructor so I can change the const data member Category (with cascading capacity if possible. I also posted some of my set functions for further comprehension.
class Book {
friend void CompPrice(Book &,Book&); //friend function that has access to the member functions of this class //The arguments sent to it are by address, and of type the class Book, so that it can have access to its member functions private: //private data members
Programe #1 // file.h class File { public: static const int var = 9; };
[Code]....
Program#1 is running fine, but program#2 gives linker error:
error LNK2005: "int GlobalVar" (?x@@3HA) already defined in file.obj
I know the header files are never compiled. Then in the above case, how the compiler knows the definition of variable var, but not able to find the definition of GlobalVar? What is the difference between this two programs?
So, I've got this class in SDL Player that has, among other things, an SDL_Texture* to hold an image that represents the player on the screen. I'd assume it's good practice to do get() and set() functions for the class; but because textures are handled via pointers, when I write a get() function I end up returning a pointer to an internal resource; which isn't good practice I hear as it "breaks" encapsulation.
Find my code below:
#ifndef PLAYER_H #define PLAYER_H #include "SDL.h" #include "SDL_image.h" #include "CTexture.h" class Player {
I recently discovered the new - new to me anyway! - feature of modern C++ that allows you to set the initial value of a data member when you declare it:
class CINTWrapper{ private: int m_iData=0; };
This even extends to calling member functions that work with initialization I believe:
class CStringWrapper{ private: wchar_t* Allocate_Array(const int iBufferSize); wchar_t* m_pString=Allocate_Array(1); };
At first, this seemed an extremely useful piece of functionality that C++ had been lacking all along. However, the more I thought about it the more it struck me this feature actually undermines one of the principle design elements of the language - that being the Constructor.
As I understand it the primary purpose of the Constructor is specifically to give the programmer a place where it is guaranteed he can always initialize his data members before anything else is done with the class. However, given the new initialization rules this is no longer necessary. So it largely seems to me that Constructors as a whole are no longer necessary either! Copy-Constructors are a special and vital case. Admittedly when I was using them for their intended purpose I hated either the redundancy you had to introduce across multiple Constructors; those with and without arguments and so on, or alternately the fine tuning of helper-functions to do common initialization between these variants. Now however I sort of regret this cast-iron rule has been taken away.
As a last point, I am trying to change the way I think about programming. I am trying to employ more objects than pure C-style ('int' or 'double', etc) data types and especially to move into templates (although absolutely NOT the Hewlett Packard template library!). Given my current understanding of inheritance in particular it seems to me that using pre-initialized data members rather than Constructor-initialization makes object derivation even more complicated, not less so.
