C++ :: Do Static Functions Have Access To Non Static Data Members Of A Class
Apr 17, 2013
From my book:
"A static function might have this prototype:
static void Afunction(int n);
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."
Why exactly cant Afunction access non-static members?
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Sep 11, 2013
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?
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Jan 17, 2013
I have a little problem with template classes and their specialization. Here is a short example:
template <typename T>
struct A{
// some typedefs
[Code]....
The above example is not compiling, because of the assignment of the const static double. Double needs a constructor, but that doesn't work (or seems not to work) with static.
I'm not sure, if it works at all in C++ that way. All I want is a template struct with some typedefs and a constant which is different for different specializations. Don't think it has to be static, but that would be better style, wouldn't it?
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Oct 15, 2013
How I can implement it.
Tickable.h
#include <list>
#ifdef TICKABLE_EXPORTS //Automatically defined by MSVS
#define DLL __declspec(dllexport)
#else
#define DLL __declspec(dllimport)
#pragma comment(lib, "Tickable.lib")
#endif
class DLL Tickable{
[Code] ....
error LNK2001:
unresolved external symbol "private: static class std::list<class Tickable*,SKIPPED BITS> Tickable::subs" HUGE_SYMBOL_LIST
PATHTickable.obj
I know with such a tiny and insignificant class the dll export seems pointless but this class is actually intended to be a .lib ONLY. But it is derived from by .dll style classes, and through inheritance this error is the exact same as what appears in the derived class, I just imagine that the cut down version would be easier to work with.
Is it possible to hold either a static variable in a dll which is of a dynamic type, OR would it be possible to reference an external variable which is static throughout the instances and this variable can be chucked away in a namespace of mine somewhere?
I suppose my only other option (if this is possible) would be to define a maximum instance number and create a standard array of pointers but this could both waste so much memory when not in use and cause problems if I need more memory.
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Aug 22, 2014
Have following code:
class Program
{
static void Main(string[] args)
{
[Code]....
My question according to what i just wrote:
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?
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Dec 4, 2014
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) {
[Code] .....
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Oct 14, 2012
I am studying the use of static data into classes and the code below is returning an error ...
#include <iostream>
using namespace std;
class REC {
private:
static int n; //Dado que sera unico na classe e alterado por todos os objetos
[Code] .....
The error:
main.obj:-1: error: LNK2001: unresolved external symbol "private: static int REC::n" (?n@REC@@0HA)
Note: I'm using QT Creator
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Jan 16, 2014
I've been having a problem concerning the initialization of const static integral members with floating point calculations. I'll let his sample program do the explaining:
class Foo {
public :
Foo() {}
const static int samplerate = 44100;
const static unsigned short tempo = 120;
[Code].....
I know you can't initialize const static non-integral types on the same line on which they're declared, but I don't see why even an implicit cast to an integral type should be disallowed. I make my calculations using doubles, so I'm surprised that even though it should degenerate into an integer - it's still a problem for the compiler.
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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.
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Jul 11, 2012
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?
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Sep 4, 2012
I am trying to use 'this' pointer but i am confused why 'this' pointer is not available for static member functions.
Code:
#include <iostream>
#include <fstream>
#include <stdlib.h>
using namespace std;
const int MAX = 20;
const int MAXPTR = 100;
class name {
private :
char fname[MAX], mname[MAX], lname[MAX];
[code].....
I am using GNU GCC Compiler via Code::Block
Error : 'this' is unavailable for static member functions
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May 15, 2013
Code:
class NavMeshLoader {
public:
NavMeshLoader() {
m_navMesh = loadAll("all_tiles_navmesh.bin");
m_navQuery->init(m_navMesh, 2048);
[code]....
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Sep 9, 2013
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)...
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Mar 1, 2014
I am creating class to be call only once in time so i am trying to implement it static to access it once i created static constructor which will be implemented within first instance of the class. My target is to pass two parameters to onstructor but as i said class should be call only once anyhow i am able to create many instances of that class which i would like to avoid and dont know how firstl i tried to create only one constructor as static with parameters but its not allow then i created static constructor and public contructor which takes two parameters but in this case i am able to create many instances:
public class HeartbeatSupervisor : ICheck
{
private Server _server;
private Protocol _protocol;
/// <summary>
/// HeartbeatSupervisor dd = new HeartbeatSupervisor();
/// </summary>
///
static int k = 0;
static HeartbeatSupervisor()
{
[code]....
inside Program Main i am able multi instances...
HeartbeatSupervisor dd = new HeartbeatSupervisor(new Server(), new Protocol());
HeartbeatSupervisor ee = new HeartbeatSupervisor(new Server(), new Protocol());
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May 11, 2013
Just wandering, will something like this work? header
Code:
#define func(arg) func_(arg) ...
static void func_(arg); code Code: #include "header"
int main()
{
func(arg);
}
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Nov 12, 2013
How does an object access its private data members in copy constructor.
The relevant part of the code: Code: C::C(const C &obj)
{
x = obj.x;
y = obj.y;
}
Normally the object1 called "obj" cannot access its private data members outside. But in this situation it can access. How can it be explained?
Here are the complete code:
Code:
#include <iostream>
using namespace std;
class C{
public:
C(int,int);
C(const C &);
[Code] .....
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Jul 12, 2013
It's hard to give a precise title but here is the question in detail: I have a class, something like this:
Code:
class classA{
public:
void fnA();
...
};
and another class that contains objects of classA:
Code:
class classB{
public:
classA A1;
classA A2;
classA A3;
vector<classA*> vA;
...
};
classB B1;
Now is it possible to access B1.vA from B1.A1.fnA() through some kind of pointer chain like this->parent->vA ? If so
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Oct 22, 2014
I am doing C++ data structures exercises, and I am still learning some of the more basic concepts. I have a parent class:
template<class T>
class linkedListType {
public:
protected:
int count;
nodeType<T> *first;
nodeType<T> *last;
private:
};
Derived class:
#include "linkedListType.h"
template<class T>
class orderedLinkedList: public linkedListType<T> {
public:
void mergeList(orderedLinkedList<T> &list1, orderedLinkedList<t> &list2) {
first = list1.first;
...
} private:
};
There is more code in my mergeList() function, but I included the line that is giving me problems. The error that my CodeBlocks compiler is giving me is that 'first' was not declared in this scope.
Strangely enough, if I change it to this->first, the error disappears.
1. Why does it not recognise 'first'?
2. Why would this->first work at all? Is the 'this' object a smart pointer?
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Oct 7, 2014
How to initialize a static member of a class with template, which type is related to a nested class?
This code works (without nested class):
#include<iostream>
using namespace std;
struct B{
B(){cout<<"here"<<endl;}
};
template<typename Z>
[Code] ,....
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May 25, 2014
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;
}
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Aug 5, 2013
Here is the code,
Code:
class A {
};
A& CreateObject() {
static A a;
return a;
} static A aa;
int main() {
return 0;
}
So is there any difference between a defined in CreateObject and aa?
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Nov 17, 2014
I have a class containing a map member that I want to initialize at declaration time. I know I can do it in the cpp file but I'm having a problem with the order of initialization (static initialization order fiasco).
My questions are:
Is it possible that the scenario in which, the Test's constructor's implementation and the map initialization instruction are in the same cpp file and constructor is called when the map is not initialized yet, could happen?
Is it possible to initialize the map in class like I did? I get these errors:
in-class initialization of static data member 'std::map<std::basic_string<char>, Test*> Test::a' of incomplete type
temporary of non-literal type 'std::map<std::basic_string<char>, Test*>' in a constant expression
If yes, does this initialization resolve the static initialization order fiasco?
class Test {
public:
static std::map<std::string, Test*> a = {};//this is an error
Test(std::string ID) {
[Code] ....
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Jul 27, 2013
What is the purpose of having static object of the same class.
E.g.
class someObj{
public:
static someObj obj;
};
how the compiler treats this object
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Mar 14, 2014
I am developing logging class and it loos like below now, my question here is I would like to avoid situation to call this class methods multiple times in same time - as I've read when I have static class or even static method (not exactly whole class) it can be call only once in time. Is this true and whether my class would pass the concept to avoid multi accessing - lets say in case of multithreading case - if one task would try to call statuc method when there is already some other trad using it.
public static class Log {
public static string EngineName { get; set; }
private static List<String> logdata = new List<string>();
public static void LogMessage(string msg, ELogflag flag, string title = "") {
StringBuilder sb = new StringBuilder();
[code]....
And my new Enum:
enum ELogflag {
LOG,
ENGINE,
CRITICAL,
CUSTOM
}
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Dec 17, 2013
it seems everytime i use statics in a class i come across with a porblem.
this time i wanted to make a class i created static inside another class.
MainVariables.h file
static fge::window mWinMain;
if someone ever wants to reach it
MainVariables.cpp file
fge::window MainVariables::mWinMain;
...
...
fge::window MainVariables::GetWinMain()
{
return mWinMain;
}
but when i created some other MainVariables classes at other places instead of them reaching to the same window two window is being created.
yes i know maybe there are better methods but currently i m working on polymorphism and i need some static members.
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Oct 10, 2013
If I need a static pointer to a class that is used globally(multiple files), and I only want to allocate memory once.
One way is to create a function that returns a static pointer of type class and call it where ever you need this pointer. My question is there another way to do this like with a header file and include the header file where you need to use the object of type class.
static class* function
{
static class c;
if (c == NULL)
{
c = new class;
}
return c
}
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