C++ :: Private Inheritance Multiple Times From Same Class
Sep 19, 2014
I've been working on a program that uses a reference counting class that I've written which works fine for objects that inherit from it however I now need to have the following setup:
class SBComponent : private Refcounted { /*stuff*/}
class ProxiedComponent : public SBComponent, private Refcounted {/*stuff*/}
The compiler gives the following warnings
warning: direct base ‘Refcounted’ inaccessible in ‘ProxiedComponent’ due to ambiguity
And then several repeats of the error:
error: request for member ‘bk’ is ambiguous
Back *b = bk<ProxiedComponent>();
bk is a templated function that's defined in Refcounted and returns a pointer of type <template arg>::Back (ProxiedComponent::Back in this case).
I don't understand why the call to bk is ambiguous as although there's two instances of Refcounted (there needs to be with the way I've designed it so I can't make it virtual) it's inheritance is private in both cases so there should only be one instance of it visible in ProxiedComponent.
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Jun 20, 2013
Here is the code:
class Foo {
public:
Foo(){cout<<"Foo"<<endl;}
};
class Bar : public virtual Foo {
[Code] ....
This is a typical implementation of multiple inheritance. If define class FooTooBar as,
Code:
class FooTooBar : public virtual FooToo, public virtual Bar {
public:
FooTooBar(){cout<<"FooTooBar"<<endl;}
};
I know why we use virtual inheritance in the class Bar and class FooToo. But if we use virtual inheritance in the class FooTooBar, does it make any sense?
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Dec 17, 2014
Write a program using inheritance allow user to enter grades of his students 5~8 students as a base class and compute the sums for each students in derived class and compute the average of sums in another derived class. I created 3 classes in 1 header file and 1 cpp file how ever i cant seem to get the sum or the average to show up on execution time
header file
#ifndef GRADES_H_INCLUDED
#define GRADES_H_INCLUDED
class Grades {
public:
Grades()
[Code] .....
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Jan 15, 2014
Let's say I have a templated base class:
Code:
template <typename Input>
class Consumer
{
public:
void consume(Input input)
{
// do something
}
};
Now, I have a class which derives from this twice (A and B are unrelated, but otherwise unimportant classes):
Code:
class A;
class B;
class Derived: public Consumer<A>, public Consumer<B>
{
};
Now, elsewhere in the code I do this:
Code:
{
A myA;
Derived myDerived;
myDerived.consume(myA);
}
This looks like it should be simple enough, but g++ 4.8.1 is giving me a "request for member is ambiguous" error.
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Apr 5, 2014
so i have to read a text file with an unknown number of lines and allocate memory to for the number of items in the text file.currently i read the entire file(counting the number of lines). i allocate memory according to the number of lines read and then use fseek() with an offset of zero to allow for the second read .
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Sep 7, 2014
I have a question about SDL and drawing sprites (SDL surfaces). My idea is that the user can create a wall of separate sprites by create one sprite each time in the current mouseX and mouseY position, when the user push down the e-key. The problem is that I have no idea how I could draw the same sprite multiple times without to delete the previous one.
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Sep 15, 2014
I've been stuck on this for hours, and have scoured the internet for any insight on this particular issue with no luck.
I'll simplify the problem here. I have a lines in an input file:
John Smith 1234 Main St New York
Carol Thomas 5678 5th Ave Columbus
...
and I am reading into character arrays using code like this:
infile.getline(name,20);
infile.getline(street,15);
infile.getline(city,10);
but when I print the output using something like this:
outfile << "Owner Name: " << name << endl;
outfile << "Address: " << street << city << endl;
(let's pretend I included spaces between the address components, which I omitted to save space)
I get an output file of:
Owner Name: John Smith
Address:
The output stops after the name variable, which I believe is stored correctly. I don't think anything is storing in the address pieces, this is the problem.
I think it's because I'm not using getline() properly in this case. Can you string together multiple getline()s like that?
If this was my design, I'd read in strings instead, but that is not possible in this case.
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Nov 6, 2014
I've been struggling with an object when trying to add it to a list with [Listname].push_back. You see, I have a list with some objects that will be rendered in the screen (Called objects) and a function to create a text box with some text. The function in question is the following:
void reprEv(int evNum, ALLEGRO_BITMAP *txtbxim) //Event to call, default text box image.
{
textBox *txtBox = new textBox("Line 1 ", "Line 2 ", "Line 3 ", "Line 4 ", "Line 5 ", textboximage);
objects.push_back(txtBox);
[Code]....
(txtNum is increased then space is pressed, and when certain screen (maxScreen) have been shown, then it will go to the playing state)
My problem begins when the text box is created, because it's supposed to add only 1 text box to objects list, but instead adds hundreds of text boxes to objects.
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Oct 6, 2013
I am writing a bit-check function just to make it easier on myself to check status flags in my classes. I use char variables and each bit represents something on or off. Since I have numerous classes that will use this functionality, it makes sense to write and compile the code only one time rather than for each class. I was thinking of writing the function and including it as a "friend" function to each class that needs it. Is that an appropriate way to do it?
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Apr 17, 2014
My application calls malloc in multiple subroutines, finally releasing all using free. This is done using my zalloc library (see my other post: [URL] .....
Somehow, when the applications tries to detect the available ammount of memory at the end of the test (allocating, freeing, testing), the freemem function gives me about 4-6MB less memory than at the start of the test? (out of 21MB available on the device at the start).
All memory is allocated and freed using the malloc/free routines within the library, with the exception of the SDL functions, which are registered externally on allocation and release.
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Oct 20, 2013
When you have to write data on a file in binary mode multiple times (without closing the file), is the put pointer left where you ended writing the last time, or do you have to use tellp() or seekp() again and again to make sure you write at the right place?
I would have the same question about the get pointer, does he stay in place after you're done reading something (without closing the file, of course), or do you have to set it back at the right place with seekg() ??
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Jun 6, 2012
Shape base class, line and Point derived classes. What should I declare in .h files and implement in .cpp files that this is array will be work.
My major concern refer to operator [] and assign (=) operator. As far as I understand I should overload ([]) and (=) three times for classes shape , line and point or not... or is it possible made through virtual function? How will be code looks like ?
Code:
// part of main.cpp
Shape* shapes[3]; // Array of pointers to Shape
shapes[0] = new Shape();
shapes[1] = new Line ("line from array ", Point(1,22),Point(33,22));
shapes[2] = new Point(11,44);
cout << "using ToString function" << endl;
for(int i=0; i < 3; i++)
cout << s[i]->ToString();
for(i=0; i < 3; i++)
delete s[i];
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Sep 4, 2014
So I have an ImageManager class, Board class, and Box class. In Board.h I can declare ImageManager imgr; and in Board's constructor I can use imgr and its functions and such. However, in Box.h when I try and declare ImageManager imgr; I get the error "cannot access member declared in class ImageManager". Both declarations are under private, and exactly the same, but one doesn't work. Also, is there a way to only have one instance of ImageManager?
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Feb 18, 2015
I am having some serious issues with class inheritance. I am trying to make a MoneyBag class inherit from a class called bag. This will not work. I get an error complaining: error: expected class-name before '{' token. And yes I have googleing it and tried several of the various solutions offered with no avail.
The MoneyBag is pretty simple right now as I wanted to get it connected to bag before I tried to do anything with it.
//MoneyBag.h//
#ifndef MONEYBAG_H
#define MONEYBAG_H
#include <bag.h>
class MoneyBag : public bag{ ////<<------ Error appears on this line.
[Code] ....
So based on everything I have seen on line the statement:
class MoneyBag : public bag{ is legal.
As it is done this way on this very site's tutorial:
class Rectangle: public Shape, public PaintCost{
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Sep 16, 2014
I have couple of objects which are using some amount of methods. Right now my application is not OOP and i am going to transfer it to OOP. So i would create each class for my each object. Almost all methods are in use for each object, the only one thing which is changing some of those objects passing not all parameters inside specific method. I can go two ways one is prepare interface for all methods i got and each of my classes could implement its own definition for it but other way almost all would implement exactly the same methods but with different parameters so maybe its better to create base class then for each object do inheritance from base class (polymorphism). inside base class i can prepare base methods and classes which will inherit from that class would override those methods for requirements they want.
So imagine: You got:
Memory
CPU
Latency
and all of them using mostly all of those same methods (only arguments for one of them could be use different way):
ExecuteQuery()
ExportToExcel()
PopulateDataTable()
PutValueToReport()
Now its better to do like this e.g:
Base class: Stuff
prop: name, id, date ...
methods to ovveride: ExecuteQuery(), ExportToExcel() ...
classes: CPU, Memory, Latency (inheriting from Stuff)
ovveride methods and align its definition for specific class use (remember mostly only passing args are used or not by specific class)
or go with inheritance
Interface SomeMethods
ExecuteQuery()
ExportToExcel()
PopulateDataTable()
PutValueToReport()
and each class would implemet its own definition.
The most important thing is that those every objects mostly using all of those methods and what is diffrence that one object can use all of available parameters inside this method and other one no. What i should do? Go with interface or inheritance and polymporfizm inside base class?
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Jan 16, 2014
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?
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Feb 27, 2014
I'm trying to implement a decision tree that gets doubles as input (in this sample code just random numbers) and returns a boolean value. At the nodes, I'd like to use various operators that can have different input and return types. I've implemented an abstract base class for the nodes and I'm deriving the specific nodes from it. In the code below, I've included only a few derived classes. Building the tree (randomly) is no problem. However, I'm looking for a clever way to evaluate the tree. I think that uncommenting the lines in bold print would in principle do it. However, this is not possible because "value" is not a member of the base class. The type of "value" is different in the derived classes, so I cannot simply declare it in the base class.
"Node.h"
#pragma once
class NodeBase{
public:
NodeBase* Child_1;
NodeBase* Child_2;
virtual void evaluate() = 0;
[Code] ....
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Sep 16, 2014
I am trying to create a few subclasses which all use the base class constructor, according to my book this is all fine and dandy by using the "using Baseclass::Baseclass", this doesnt work for me.
class Monster {
public:
Monster(char[], char[], char[], int); //The constructor, and its implemented.
etc..
};
[Code] ....
Yet, i recieve this error:
error LNK2019: unresolved external symbol "public: __thiscall Human::Human(char * const,char * const,char * const,int)"
Why is this? Does doing it this way create const pointers somehow? The constructor works fine with Monster, i am using the same calls, just changed to create Human instead of Monster. All files are included where they should, monster and human are declared in the same header.
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Nov 10, 2014
In this assignment the student should develop a month calendar by designing a class called calendarType . This class uses two other classes (dateType and dayType) as described below:
1. dayType Class: This class has been designed by students in Lab1 exercises. Referee to it.
2. dateType Class: This class is designed and implemented to keep track of data. This class has been provided it to you. Study it first then add definitions and implementations of the following operations to this class:
- Test whether the year is a leap year. Leap year is identified by 3 criteria :
- The year is evenly divisible by 4;
- If the year can be evenly divided by 100, it is NOT a leap year, unless;
- The year is also evenly divisible by 400. Then it is a leap year.
- Return the number of days in the month. For example, if the date is 12/3/2014, the number of days to be returned is 31 because there are 31 days in March.
- Return the number of days passed in the year. For example, if the date is 18/3/2014 the number of days passed is 77. Note that the number of days returned also includes the current day.
- Return the number of days remaining in the year. For example, if the date is
18/3/2014 , the number of days remaining in the year is 288.
- Calculate the new date by adding a fixed number of days to the date. For example, if the date is 18/3/2014 and the days to be added are 25, the new date is 12/4/2014.
To print monthly calendar using calendarType class, you must know the first day of the month and the number of the days in that month. Thus, you must store the first day of the month, which is in the form of dayType and the month and the year of the calendar. Clearly, the month and the year can be stored as an object of the form dateType by setting the day component of the date to 1, and the month and year as specified by user.
Design the class calendarType so that the program print a calendar for any month starting 1/1/ 1500 which is Monday. To calculate the first day of a month, you can add the 2 appropriate days to Monday of January 1, 1500. For this class identify and implement the following operations:
- Determine the first day of the month for which the calendar will be printed. Call this operation firstDayOfMonth.
- set/get month.
- set/get year.
- Print calendar for particular month.
- Add the appropriate constructors to initialize the member variables.
- Write a test program to print the calendar for either a particular year or a particular month.
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Aug 9, 2014
Why do you use Private fields in a class if an outside class can change the private fields using get and set properties?
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Apr 4, 2014
I am trying to access the private member from main . The code is as follow. I wanted to call below function from main.
uint16_t Modbus::calcCRC(uint8_t u8length)
#define MAX_BUFFER 64
typedef struct {
[Code]....
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Dec 11, 2014
i have private data look like Peiceorder peiceOrders[20]; it looks like a array but does not have name type like int or char? why is that and what should I use the data should I write Peiceorder peiceOrders[20]=........ like that? or?
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Oct 30, 2013
I have a class (Quadtree) and three inner class inside (Node, Inner and Leaf). Inner and Leaf inherit from Node.
I have a function in the private scope of Quadtree.
All these are located in fun.h .
Then, in fun.cpp, I am implementing the function (which is named foo <- what a prototype name!), which takes as argument a pointer to an Inner object. Inner seems unable to be resolved however!
fun.h Code: class Quadtree {
private:
class Node{
public:
Node() { std::cout << "Node
"; }
};
class Inner : public Node {
public:
Inner() { std::cout << "Inner
[code]....
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Sep 30, 2014
I want to make a destructor counter...So it needs to be outside that specific instance of the class. And i want to keep it hidden. I don't want to be able to access it from outside the class...I Don't want main.cpp to have access to this variable
Is there a way to do this?
static int destructorCount;
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Feb 16, 2013
I get a problem with the vector as a private class member: When I did't initialize the vector in constructor(which means the size of the vector would be 0), I used a class function to add two elements to the vector and it worked (because I added a "printf" to output the size of the vector and the elements within that function). However, when I used another class function to visit that vector, no element was in and the size became 0.
Then I tried to add two elements to the vector during the construction, and it turned out that these two elements could be stored in the vector while other elements added through class functions could not.
I guess there may be some problems on the scope of the function. But I feel the class member should not be effected by the scope of the class function.
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Oct 24, 2013
This question is more from a design point-of-view rather than coding it to be a fully functional.
So here it goes:
I have multiple files which each require their own object of same class type (ref. First Class). File contents are read from a file to a unordered_map<std::string, std::vector<std::string>> which is either private or protected member inside First Class. First Class does not need any public functions to add, remove or change the data during runtime, but changes are only being made by checking if the file size has changed during the day, if the size is not equal to the last check, map gets updated.
Now, I have a Second Class which is a data handler class. It has public member functions with arguments that needs to be get from First Class's unordered_map using const_iterator. Which way to go with design and implementation.
I know there's two methods to do this. Re-doing handler class is also not out of the question. These two methods I'm aware of are:
1. Declare these maps to local scope, build few global functions and here we go. (Probably the easiest way.)
2. Create public member functions to a First Class which either return a pointer or a reference to a protected/private member. (I'm under the impression that I really shouldn't be doing this because of a bad coding practice.)
Note that I don't need any code here, just some other point-of-views regarding the subject itself for learning better coding practices.
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