C++ :: Can't Initialize Static Data Member In The Class Definition
Apr 17, 2013
"You cannot initialize the static data member in the class definition — that’s simply a blueprint for an object and initializing values for members are not allowed. You don’t want to initialize it in a constructor, because you want to increment it every time the constructor is called so the count of the number of objects created is accumulated."
Why don't you want to initialize it in a constructor?
Edit: Because every time it is called it will set it back to 0 or whatever the initializing value.
For example, in a header file A.h, I define an abstract class,
Code:
// A.h class A { public: virtual void foo() = 0; private: static int _x; };
How'd I initialize static member data _x?Normally, we initialize a static member data in a cpp file. However, there is not cpp file for A.h. If I intialize _x in header file, there will be linker errors like mulitple defined symbols. What is appropriate way to do that?
Basically I want to create a base class which defines a static data member so that its automatically redeclared as the same static data member in the derived class.
class A{ protected: static derivable int val; // A::val }
class B : public A{ // static derivable int val is already here // A::val AND B::val }
This seems impossible to me but I'm wondering if perhaps there's a way to add modifiers to the compiler to do this (or preferably something MUCH simpler)...
#include "stdafx.h" #include <iostream> #include <math.h> using namespace std; class Calc {
[Code] ....
when i built it, it showed the following errors:
1>------ Build started: Project: rough, Configuration: Debug Win32 ------ 1> rough.cpp 1>e:c programs ough ough ough.cpp(17): error C3872: '0xa0': this character is not allowed in an identifier 1>e:c programs
A static function can be called in relation to a particular object by a statement such as the following:
aBox.Afunction(10);
The function has no access to the non-static members of aBox. The same function could also be called without reference to an object. In this case, the statement would be:
CBox::Afunction(10);
where CBox is the class name. Using the class name and the scope resolution operator tells the compiler to which class Afunction() belongs."
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; }
I have a class having static member.I have get and set methods which will Get and Set Values to this variable. In a multithreaded application does it have any thread safety issues.
Class a { static int b; void Set (int c); int Get(); };
I am writing my program on C++ language. I have one promblem. I need to set signal handler for my process. As the signal is related with the process on system level I have faced the problem.
My program consists several classes. They are connected together. But it doesn't metter in this case. The problem is that I need to access to member and methods of the class from my signal handler. For instance , I have class named Foo at it has some members and methods.
So from my handler I need to call its function and change members.
I understand that compiler should know that this class instances will exist during all program execution.
I have tried to set static member class Foo instance in another class , but this didn't solve the problem.
What is correct approach to do this. How to correctly implement signal handling in such case.
Here is example of my code
Code: class MyContainer{ private: std::vector<Foo> container; public: int removeFromContainer(Foo* aFoo) {
What are the workarounds for accessing the non-static member variables of some class(Say A) inside static member functions of another class(Say B)? I am coding in c++. Class A is derived with public properties of class B. Any pointers?
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.
I have a small class with a static int data member. I want to zero init it. I am thinking that making a .cpp file with only one line seems too much, isn't it?
So, can I do it inside the the header file? The variable is going to enumerate how objects were created (so any alternative will do).
I have to implemente the to_string method. Whats the fastest way? Stringstreams. But I have to use C++ without any headers, so I need to implement the stringstream class. How can an stringstream hold one float? An double? Hoq cqn I implement an strigstream myself?
1. Is that mean that Do() is only available for use by Dog itself because Dog is 'oryginal' Dog, and if i create new dogs - instances of oryginal Dog (dog1, dog2 ...) they cant access because Do is only available fo 'oryginal' one? Is that correct thinking?
2. If i would want to have something common (e.g value) for all dogs is that good way to create static field/method for Dog instead of non-static once then all instances of Dog would access Dog static member to get/change it? Just stupid example: static method GetAmountOfLegs() which return 4 Then all instances can take/call that value from Dog. Is that correct thinking?
#include "IMyIntData.h" class MyIntData : public CPMUnknown<IMyIntData> {
I need to know what this syntax means (including MyIntData in angular brackets after parent class name) where IMyIntData is the Interface from where MyIntData is derived.
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).
Write a class definition for a Fraction class. Its member fields are num and den, both of type int. The constructor builds the default fraction 1/1. It has the following operations:
void plusEquals(Fraction second); //Adds the second fraction to this fraction like the operator += void minusEquals (Fraction second); //Subtracts the second fraction from this fraction void timesEquals (Fraction second); //Divides this fraction by the second fraction void dividesEquals (Fraction second); // Divides this fraction by the second fraction void reduce(); // Reduces this fraction to lowest terms double todecimal(); //returns the decimal value of this fraction void scan(istream&); //scans a fraction written with a slash as in ¾ void print(ostream&); //prints a fraction using a slash Fraction(); //constructs a default fraction with denominator 1, numerator 0 Fraction(int n, int d); //constructs a fraction given value for num and den
2. Write a menu-driven driver program designed to allow thorough testing of your Fraction class.
