C/C++ :: Pointing Variable To A Member Function Outside A Class
Apr 13, 2012
In C++, how do i call a method member of class A from a class B, using a pointer. By the way Class A and B are of different types.
I read that when a pointer is pointing to member function it can only point member functions within the class. But how can i point to a member function outside the class.?????
The question is: Define the class Counter. An instance of this class is used to count things, but the counter should never be less than 0 (non negative number). The member variable should be private. I realize what I'm suppose to be using but can't implement the member functions needed..
int main(){ int value; cin >> value; Counter myCounter(value); for (int i = 1; i <= MAXLOOP; i++) { myCounter.increment();
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; ????
I need to keep a static variable in a member function of a class that I have many objects of. I've had some trouble with it, and when I read up I found that such variables are static across all instances. Is there any way around this?
#include <iostream> #include <array> #define x arr[0] #define y arr[1] #define z arr[2] class Point {
[code]....
... that is, to be able to reference the same data by "member variables" as by referencing a stl container. But defines are the devil's work - adding in a "#define x arr[0]" is a dangerous statement. I'd really like some nice clean C++ method (C++11 or C++14 are just fine) to do this without defines, but so far I'm drawing a blank. If arr wasn't an STL container, if we just wanted a pointer-based array, I could do it this way:
class Point { ... float x __attribute__ ((aligned (sizeof(float)))); float y __attribute__ ((aligned (sizeof(float)))); float z __attribute__ ((aligned (sizeof(float)))); float*const arr = &x; };
... but you obviously can't do that if arr is an STL container.
The best I've come up with is to make x, y, and z function pointers, but then you can't call them like p.x, you have to call them like *p.x(), it's not very clean and I'd expect some added overhead. One could go even uglier and make x, y, and z be instances of some custom class with overridden operators that reference arr[], but that seems like it'd be just getting ridiculous in terms of overhead (both coding and performance)
Would each instance of Foo create a new counter variable, or would it remain the same for all of them, i.e. baz.funky() would always use the same counter variable? What if the class was a template?
I am writing a program which is using SDL library. I have two different classes which one of them is Timer Class and the other is EventHandling Class.
I need to use some member functions and variables of Timer in some Eventhandling Class member functions, Although I want to define an object of Timer in int main {} and relate it to its member function that has been used in Eventhandling member function in order that it becomes easier to handle it, I mean that I want to have for example two objects of timer and two objects of Eventhandling class for two different users.
I do not know how to relate an object of a class from int main{} to its member function which is being used in another class member function.
So I have a class object that contains the private member variable spot and the public member function MoveLock. Within MoveLock, is a member variable called numbers that holds the place where a user is on a "lock knob". Now, what I'm trying to accomplish is that whenever the user turns the "knob" in the wrong direction, the position is updated with that current numbers so that the clicks needed to unlock the first state is also updated. But I get these errors:
Error E2096 C:Users...switchtest.cpp 34: Illegal structure operation in function main() Error E2294 C:Users...switchtest.cpp 39: Structure required on left side of . or .* in function main()
Ultimately, what I have in main() is a piece of what I'm going to implement in a class member function. I'm also thinking about moving the if else statements out of the for and creating a second one for the else portion.
I am modifying a set of static variables inside of the class's member function. The static variables are private. An example of what I'm doing is as below,
utilities.h ----------- class utilities { private: static int num_nodes;
public: void parse_details(char* );
[Code] ....
I get a compilation error in the function void utilities::parse_details(char* filename)
which says: undefined reference to `utilities::num_nodes'
I mount a function (parameter - numeric vector; returns a string). However, this same function is used in several classes. To avoid that I keep duplicating the same code within these classes there is a way to do that as the code below?
std::string func( const vector<int> vec ) { //processamento return result; } class A {
I want to have a template function that is a member of a class. Is this possible? This code snippet is how I would think the syntax would go, although it doesn't compile. How would I achieve the same effect?
Code: class myclass { public: int member ; } ; template <typename T> void myclass::func( T& arg )
I keep getting an error saying ui.h:30: error: 'class BTree<Word>' has no member named 'prntInOrder' I have no line 30 in my ui.h but if i count the lines from the .cpp as if they were attached to the .h i find the call to the BTree printInOrder()
here is my ui.h
Code: #pragma once #include "btree.h" #include <fstream> #include <iostream> using namespace std;
[Code].....
As you can see the printInOrder() function is there so would it not see it?
Error:
Code: ui.h: In member function 'void UI::go(std::string)': ui.h:30: error: 'class BTree<Word>' has no member named 'printInOrder'
I have a class I am building called date and I've built all my functions to run and done all the necessary error checking in each function. However, my last and final function I have to write is where the # of days passed in as a parameter and then I have to increment the days by that many. And if the user does not increment any days at all in the parameter and leaves it blank, then it automatically increments by one day. I am having trouble with this. So for example if the user was to do this:
Date d1(10, 31, 1998); // Oct 31, 1998 Date d2(6, 29, 1950);// June 29, 1950
d1.Increment(); // d1 is now Nov 1, 1998 d2.Increment(5);// d2 is now July 4, 1950
The function starts out looking like this
void Date::Increment(int numDays = 1) { }
I know I have to use a for loop to accomplish this. I just don't know how to get it to where the days passed in will go to the next month and then days passed in would go to the next year.
Some background: I have a class, A, with members, B and C and D; I also have an array of A objects; I want to be able to have a function which takes said array and performs a certain calculation on either the B, C, or D members of each of the A objects, depending upon certain circumstances; I want to perform the same calculation regardless of which member is to be used in said calculation, such as always assigning the value 3 or multiplying the member's value by a cofactor of some sort.
My question, therefore, is: how I might do this using only one function be it a template or not?
I understand that the files using the exported class or function need to call this class or function with dllimport and the file containing the exported class or function needs to call this class or function with dllexport. But I tried to use __declspec(dllexport) only instead of the statements above. It still works. Is there anything I am missing?Why'd we have to switch between dllexport and dllimport?
I have a simple question about inheritance. Consider the following code:
Code: Class Base { int type; Base(){}; }; Class Derived1 : public Base
[Code] ....
I get the following error: Class "Base" has no member "Function1";
That makes sense - as Base has not declared Function1. But how can I loop through a vector of Bases, and then if the object is of type Derived1, call the function Function1?
I'm currently programming a server which uses multiple threads- I have a class for one map in the game. Each map has a thread for timed events(tile regeneration, NPC regeneration, etc.), and a thread for handling NPCs(movement, combat, etc.). A basic structure of the class looks like this:
class Region { public: /* game values are here, they are public so they can be accessed from outside of the class inside of packet-handling functions and such */ int value; void *Function();
[Code] ....
The program crashes when I use a member of the same class the function is located in- in the context I have shown about it would crash on "value++".
I am supposed to implement the member functions of class Person.
class Person { public: Person(); Person(string pname, int page); void get_name() const; void get_age() const;
[Code] ....
The code I wrote is below. Where I am struggling is the program does not allow me to input age. Therefore, I cannot test if my temp for age works. It automatically defaults to 0 because it hasn't taken input. Here is my code:
// Program Title: Person function // Program Description: The program prompts the user for first and last name and age. // It then prints the output that was provided by the user.
#include<iostream> #include<string> using namespace std; class Person {
I am having trouble compiling my interface. I am trying to store a reference variable as a member variable of the interface object. Compiler says that the variable has not be initiated correctly.
LCD inherits from VisualInterface which is expecting a DisplayDriver object to be passed in (DisplayDriver is another interface, but thats not important).
I pass the displayDriver object in when LCD is instantiated in maininterfaces.zip
I was pasing it before as a pointer but was told that this could cause me problems with memory leaks and a reference was better, but now I cant seem to get it to compile.
We're assigned a project working with classes and fractions. My goal is to display a fraction in proper from based on 2 arguments passed to a class member function proper();
My strategy was to utilize the greatest common factor between the 2 arguements, then divide both the numerator and denominator by that number and then it would display.
The program actually runs, but only seems to divide the numerator and not the denominator. This in return makes my other class member functions have incorrect comparisons and sums.
Code: #include<iostream> #include<conio.h> class Fraction { friend void compare(Fraction a, Fraction b); friend void sum(Fraction a, Fraction b);
