C++ :: Can Use Class Constructor To Run Code In CPP By Itself?
Jan 13, 2015
I recently designed a struct like this
// MyMap.h
typedef std::map<std::string, std::function<void ()>> MyMap;
extern MyMap g_mymap;
// MyMap.cpp
My Map g_mymap;
[Code] ....
It looks useful to implement strategy pattern because it makes a fully separate code block. So I can add a function to the map simply by compiling a source file. It's very simple. I don't need to edit another file.
But when I use it for my existing project, It makes some linking and runtime errors.(vs 2012). I can't recognize exactly why because it is a huge project. Anyway, I have a question that - Is this a safe use of class constructor?
I know that there is no fixed order of running, but in this case I think it doesn't matter. because they are independent. But it is not a common pattern, so I can't decide to use it.
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Jan 1, 2013
Is this example correct? This example from a book
Constructor of the Base Class
Person::Person(char* n="", char* nat="U.S.A", int s=1)
{
name = n;
nationality = nat;
sex = s;
}
Constructor of the Derived Class (inherited from the base class)
Student(char* n, int s=0, char* i=""):
Person(n, s)
Why the initialized list of the base class constructor doesn't match the initialized list of the derived class constructor? I know this book is a little bit old, I'm not sure if this wrong in VC++ 2010?
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Mar 19, 2015
to initialize this object? Why C++ FAQ says no? Here is my code,
Code:
class A
{
public:
A(int x, char c);
A(int x);
[code] ....
I don't have any trouble to call the constructor A(int x, char c) from another constructor A(int x).
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Jan 6, 2015
Let's say I have a Car object , and it contains inner Engine object.
Code:
struct Car{
Engine mEngine;
};
In order to initialize the engine object NOT by the default constructor (if it has any) , we use initialization semantics:
Code:
Car::Car:
mEngin(arg1,arg2,...)
{
other stuff here
}
Now it gets tricky: Let's say a Car objects has 10 inner objects, each object has about 5 variables in it . Car is a base class for , e.g. , Toyota class. you don't want the Car class to have a constructor with 50 arguments. Can the inner objects of Car be initialized from the base class , e.g. Toyota?
Code:
class Toyota:
Car(...),
mEngine(...),
mGear(..)
{
...
};
The other options are:
1) like said , create a Car constructor which gets 50 arguments, then initialize Car as whole from Toyota - the code becomes less readable and less intuitive
2) Car constructor which get built-objects as arguments and initialize the inner objects with copy constructor . the code gets more readable but then you create many excess objects .
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May 15, 2013
I understand it is done like this
// Calling the base class constructor
explicit CCandyBox(double lv, double wv, double hv, const char* str="Candy"): CBox(lv, wv, hv)
{
...
}
But how does the compiler know that you are initializing the base "part" of the object?
Or is this the entire reason initialization lists exist, to separate this confusion?
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Feb 28, 2012
I am trying to use constructor within constructor in the same class. Is that possible. I have tried something and it shows me a error message:
error: type "mainClass" is not a direct base of "glavna"
This is the program I tried:
Code:
class mainClass {
private:
int x,y;
Code] ......
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Sep 20, 2013
Suppose I have two classes A and B so how to access object of class A in constructor of B's class as a parameter.
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Apr 13, 2014
I have a class 'A' which is almost perfect for my needs. Class 'B' uses class 'A' I've now designed Class 'C' and Class 'D' and noticed that there is a good chunk of code in class 'B', 'C' and 'D' for using Class 'A' is duplicated. I've separated out this code in specific, standalone functions in each of the classes. Now I'm wondering where this code should go. At the moment, the functions are duplicated in the three calling classes (B, C and D). Placing the functions into class 'A' would break the single responsibility principle. Inheritance to add functionality would likely break both SRP and LSP. The one that seems that it may work is composition.
However, Is designing a complete class just for a few functions over kill?
Would it be valid for classes 'B', 'C' and 'D' to access both the new class 'E' (which would depend on A) and the old class 'A' (which would have to be the same instance as the instance in the new class 'E'), or should the new class 'E' provide sufficient functionality so that Classes B, C and D don't need to access Class A directly? It would seem that its then an incomplete interface of the original object with additional functionality (ie, incompatible) Or should I do it a completely different way?
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May 29, 2013
I really confused with constructor (default constructor and constructor with parameters)
I coded this problem
and I worked almost, but I stock in constructor
Code:
class Tier {
public:
enum TIER_MAKE
[Code] ....
This is tier class and I have to finish constructor in class car (for simple, I skip detail code) -red things are the parts from class Tier
Code: Car()
: make(NULL), passengers(0), fuelcap(0.0), efficiency(0.0), tier(Tier::nexen)
{ }
[Code] ....
And someone said default constructor part has to be this
Code:
car( Tier::TIER_MAKE p_tiermaker = Tier::nexen )
//after i skip
but default constructor should be no parameter...? isn't it?
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Mar 22, 2014
# include <iostream>
# include <cstring>
#include <iomanip>
#include <cmath>
using namespace std;
class Course
// Creating the class Course
[Code] ....
Errors: Warning1warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.
[Code] .....
I have to create an Array of type Course and then fill its member dats using various member functions. Those errors are caused by some Constructor defect, which I dont really know what it is.
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Nov 15, 2012
This is my class there is a problem with my copy constructor .. is that correct ??
struct Node {
Type info;
Node<Type> *next;
};
template <class Type>
class Queue
[Code] ....
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Jul 14, 2014
Firstly I don't really know if this is possible.
This is my Class Diagram: [URL]...
github: [URL]...
I want to redefine the price object of the Book Class. However price is defined at Products Class.
I want the price value change according to the marker value, which is a Book attribute.
If the marker is blue, price gets a value of 10 (e.g.), if it has another value, price is equal to 20.
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Jun 27, 2013
Basically, I need to set a variable outside of the constructor and make it accessible to the entire class.
It would need to work something like this:
#include <iostream>
#include <string>
template <typename MT> class CallbackFunction
{
[Code].....
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Feb 14, 2013
I am making a snake game just to give some context.
//LevelObject.hpp
class LevelObject {
public:
virtual void Update() = 0;
virtual void Draw(Canvas& canvas) = 0;
protected:
Vector3 location_;
[Code] ....
The problem I have is with the Size constructor and the abstract class LevelObject which size is a member of.
The compiler error I get is:
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
[Code] .....
However I do invoke the copy constructor when I pass a variable of type size to the constructor in this line:
size_ = Size(s);
But the problem is that its complaining that the abstract class LevelObject doesn't invoke the constructor, which it shouldn't.
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May 17, 2013
When the below is done, does it call the constroctor only, and if yes, constructors do not have return types so how does it work? is there anything behind the scene?
wxAddHandler(new wxPNG_HANDLER);
and
sf::RenderWindow(sf::VideoMode(...),...);
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Mar 12, 2012
Can I determine if a templated class has a particular constructor, in my case using a string within function to which T is used?
Code:
template<class T>
void MakeObject(std::vector<T>& dataVector)
{
std::string str "con string,Joe,24";
// catch if T has string constructor
T someObject(str); // T someObject should have constructor from string
dataVector.push_back(someObject);
}
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May 5, 2013
I am unable to understand how a move constructor works in this example of code. If someone could break down the process of what is taking place and explain to me on why to use a move constructor.
Code:
class MyString {
MyString(MyString&& MoveSource) {
if( MoveSource.Buffer != NULL ) {
Buffer = MoveSource.Buffer; // take ownership i.e. 'move'
MoveSource.Buffer = NULL; // set the move source to NULL i.e. free it
}
}
};
Example from "SamsTeachYourself: C++ in One Hour a Day"
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Mar 7, 2015
I keep getting following errors:
multiple definition of `SDL2Graphics::SDL2Start()'
undefined reference to `SDL2Graphics::SDL2Graphics()'
My set up is as follows:
Main.c++:
#include <iostream>
#include "GL/gl.h"
#include "GL/glu.h"
#include "SDL2graphics.c++"
/* Global variables */
int main(int argc, char* argv[]) {
[Code] ....
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May 1, 2013
I am trying to pass an object to an inherited clas by a constructor. I am having Cboard my board and i need to pass it to the object Cpawn.
Here under is my code:
main
Code:
#include<iostream>#include "Cboard.h"
#include "Cpawn.h"
#include "Cpiece.h"
void main(){
char location[50];
[Code] ....
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Jun 18, 2013
I have three classes 1 base and two inherited.. problem is when I try to initialize the it says undefined reference to vtable constructor.
Code:
#ifndef QUOTE_H_INCLUDED
#define QUOTE_H_INCLUDED
#include <string>
using namespace std;
[Code] ....
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Mar 25, 2013
I'm trying to make a class constructor within a namespace and I keep getting errors like: "'<variable>' is a nonstatic data member of class '<class>'" for when I try to setup parameters, and "Incomplete type is not allow" whenever I try to write out my function definition. Here's what I'm doing:
namespace test {
class blah;
} class blah {
typedef int var[5];
[Code] .....
Also I'm unsure why there is a parameter of 'const blah &' when I mouse over blah(); (using Visual Studio 2010) within the class definition. It tells me 'blah::blah(const blah &)' and I am unsure where the parameter comes from. How can I resolve these issues?
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Nov 14, 2013
I'm writing a class that has two constructors. However, I can't get them to work quite right. One constructor has a parameter of an int (with a default value of 0) and the other has a parameter of a C-style string.
First of all, are these function prototypes correct for the constructors?
MyInt(int n = 0);// first constructor, int param, default value 0
MyInt(const char * c);// second constructor, c-style string param
Both constructors work fine in some cases but don't work in all cases. Here are some potential calls to these functions that are supposed to work:
// These two work fine
MyInt x(12345),
y("9876543210123456789"),
// The array assignment doesn't work when the value is negative
// I'm not allowing negative numbers, but I want to create the object and assign the array to 0
r1(-1000),
[Code] .....
Here's the private data from the class (from the header file):
private:
int currentSize,
maxSize;
char* digits;// Pointer to an array of digits
// Increase the size of digits array by 5
void Grow ();
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Jul 27, 2014
I have one base class and one derived class.
class Base
{
protected:
int a, b;
[Code]....
The two definition of the derived class constructor
(Derived(int aa, int bb, int cc) { Base(aa, bb); c = cc; }
and
Derived(int aa, int bb, int cc) : Base(aa, bb), c(cc) {}
looks identical but first one does not work.
So, I wounder what the difference between them?
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Apr 23, 2013
I'm making a little "game engine" for a Rogue-Like game series I'll develop beside a friend. This "game engine" was programmed originally in ms-dos batch 6 years ago by me, and was evolving since. It have a VB6 version, a VB .net version, and a Python version... lately a C++ version following the same method of the first stable release of ms-dos batch (isn't weird?). As you can see, is a mere hobby.
Well, I have 1 headers for my C++ version of the engine, in that *.h file I have 2 classes (for now). The first class, and maybe the most important one, contains the code of the map handling (drawing, verification, creation, modification etc.) and the second one is the Object class, which code the "actors" or "npc" basic functions as movement, coloring, instancing etc...
The second class depends of the first class to function, because the first class is the responsible of displaying all inside the map.
The problem is that the class Object needs an instance of the class Map where the Object will be, but... that's the problem, the code seems right, but when is about to run it crash reporting a "No matching function for call to 'Map::Map()'" in the line 91 of AGE.h (that's the Object class constructor)... and its all.
So, this is the code of the main header that contains these classes:
#include <iostream>
#include <stdlib.h>
#include <conio.h>
#define Up 0
#define Down 1
#define Left 2
[Code] ....
A simple code that uses "AGE.h" for test purposes...
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Feb 10, 2014
I am having trouble creating a new User from my User Class. The error I am recieving:
Error3'HospitalSystemBL.User' does not contain a constructor that takes 2 argumentsC:UsersStudentdocumentsvisual studio 2010ProjectsHospitalSystemHospitalSystemLogin.aspx.cs2131HospitalSystem
In my User class, I have two constructors. Default and an overloaded constructor.
//default constructor
public User() {
}
//overloaded
public User(long UserName, string Password)
[Code] ....
I am trying to create my user in my Login class. Why is the error saying "does not contain a constructor that takes 2 arguments" when I have a constructor (above), User passing two arguments: UserName and Password? Here is my code for the login:
protected void btnLogin_Click(object sender, EventArgs e) {
try {
int Userid = Convert.ToInt32(txtUser.Text);
string password = txtPassword.Text;
[Code] ....
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Jul 27, 2012
As i have one Abstract base class say MyBase.
It have parameterized constructor with string value it have abstract method call.And I also have One child class say MyChild.
It does not have any constructor only one have public method and i want to call that parameterized constructor of base class onto child class.
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