No Default constructor to run functions in c++? - c++

Question

i want to run the function Run in the main, but am not allowed to create object due to no default constructor. when i try to create the default constructor, i receive the message, 'Error"Game::Game int maxComponents)" provides no initialiser for:'
//Game.h
#pragma once
#include "GameComponent.h"
#include <time.h>
class Game
{
private:
int componentCount;
GameComponent** components;
const int TICKS_1000MS;
public:
Game(){} //this does not work either
Game(int maxComponents){} //this does not work as my default constructor
~Game();
void Add(GameComponent*);
void Run();
};
//Game.cpp
#pragma once
#include "StdAfx.h"
#include "Game.h"
#include <iostream>
#include<time.h>
using namespace std;
void Game::Add(GameComponent*)
{
components= new GameComponent*[componentCount];
}
void Game::Run()
{
time_t rawtime;
struct tm * timeinfo;
time ( &rawtime );
timeinfo = localtime ( &rawtime );
//cout << timeinfo->tm_hour<< ":" << timeinfo->tm_min << ":" << timeinfo->tm_sec << endl;
for(int n=0;n<componentCount;n++)
{
components[n]->Update(timeinfo);
}
}
Game::~Game()
{
}
//main.cpp
#include "stdafx.h"
#include <iostream>
#include "Game.h"
#include <time.h>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
Game obj1;
obj1.Run();
system("pause");
return 0;
}
So, how do i create a default constructor here? i've tried to use member initialising too, doesn't work. and copy constructor.

Answer 1

A default constructor is a constructor that takes no arguments. So, you should declare a constructor that looks something like this:
Game() { }
You can keep your other constructor - normal function overloading applies to constructors, so it will use your Game(int) constructor when you specify a single integer argument, and Game() when you specify no arguments.
However, in your case Game contains a const int member (TICKS_1000MS). Since it's const, it's expected to be initialized in the constructor. So you should do something like this:
Game() : TICKS_1000MS(123) { } // replace 123 with whatever the value should be
You need to do that for all constructors.
It's a little silly to have a non-static const member of a class which is always initialized to the same value (as opposed to a value passed in as an argument to the constructor). Consider making it an enum instead:
enum { TICKS_1000MS = 123 };
or, a static const member:
static const int TICKS_1000MS;
and initialize it in Game.cpp:
const int Game::TICKS_1000MS = 123;

Answer 2

As long as you have defined a constructor other than than the default one, the default constructor is not provided anymore so you have to define it manually:
public:
Game() {}
Game(int maxComponents){}
Now you have a default constructor and an overloaded constructor which takes 1 integer parameter.

Answer 3

You will need to create the default parameterless constructor. When you define a constructor you no longer get the default that would have been created behind the scenes.
Game(){}

Answer 4

The default constructor is the one that does not take any parameters, in your case Game(){}.
You do not seem to use the constructor parameter, but if you do, you will have to provide a default value.

Answer 5

Probably you can so something along these lines, you class Game needs to initialize const int in both the constructors:
class Game
{
private:
int componentCount;
GameComponent** components;
const int TICKS_1000MS;
public:
Game(): TICKS_1000MS(100)
{} //this does not work either
Game(int maxComponents): TICKS_1000MS(100)
{} //this does not work as my default constructor
~Game();
void Add(GameComponent*);
void Run();
};
As pointed out by others you need to intialize const data in ctor or initializer list.