C++ 如何使用构造函数在另一个类中创建对象？

How to create an object inside another class with a constructor?

提问by Rivasa

So I was working on my code, which is designed in a modular way. Now, one of my classes; called Splashhas to create a object of another class which is called Emitter. Normally you would just create the object and be done with it, but that doesn't work here, as the Emitterclass has a custom constructor. But when I try to create an object, it doesn't work.

所以我正在研究我的代码，它是以模块化方式设计的。现在，我的一堂课；被调用Splash必须创建另一个被调用的类的对象Emitter。通常，您只需创建对象并完成它，但这在这里不起作用，因为Emitter该类具有自定义构造函数。但是当我尝试创建一个对象时，它不起作用。

As an example;

举个例子;

Emitterhas a constructor like so: Emitter::Emitter(int x, int y, int amount);and needs to be created so it can be accessed in the Splashclass.

Emitter有一个像这样的构造函数：Emitter::Emitter(int x, int y, int amount);并且需要创建以便在Splash类中可以访问它。

I tried to do this, but it didn't work:

我试图这样做，但没有奏效：

class Splash{
    private:
        Emitter ps(100, 200, 400, "firstimage.png", "secondimage.png"); // Try to create object, doesn't work.
    public:
       // Other splash class functions.
}

I also tried this, which didn't work either:

我也试过这个，这也不起作用：

class Splash{
    private:
        Emitter ps; // Try to create object, doesn't work.
    public:
       Splash() : ps(100, 200, 400, "firstimage.png", "secondimage.png")
       {};
}

Edit:I know the second way is supposed to work, however it doesn't. If I remove the EmitterSection, the code works. but when I do it the second way, no window opens, no application is executed.

编辑：我知道第二种方法应该有效，但事实并非如此。如果我删除该Emitter部分，代码将起作用。但是当我用第二种方式做时，没有窗口打开，没有应用程序被执行。

So how can I create my Emitterobject for use in Splash?

那么如何创建我的Emitter对象以用于Splash？

Edit:

编辑：

Here is my code for the emitter class and header: Header

这是我的发射器类和标题的代码： Header

// Particle engine for the project

#ifndef _PARTICLE_H_
#define _PARTICLE_H_

#include <vector>
#include <string>
#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include "image.h"

extern SDL_Surface* gameScreen;

class Particle{
    private: // Particle settings
        int x, y;
        int lifetime;
    private: // Particle surface that shall be applied
        SDL_Surface* particleScreen;
    public: // Constructor and destructor
        Particle(int xA, int yA, string particleSprite);
        ~Particle(){};
    public: // Various functions
        void show();
        bool isDead();
};

class Emitter{
    private: // Emitter settings
        int x, y;
        int xVel, yVel;
    private: // The particles for a dot
        vector<Particle> particles;
        SDL_Surface* emitterScreen;
        string particleImg;
    public: // Constructor and destructor
        Emitter(int amount, int x, int y, string particleImage, string emitterImage);
        ~Emitter();
    public: // Helper functions
        void move();
        void show();
        void showParticles();
};

#endif

and here is the emitter functions:

这是发射器功能：

#include "particle.h"

// The particle class stuff
Particle::Particle(int xA, int yA, string particleSprite){
    // Draw the particle in a random location about the emitter within 25 pixels    
    x = xA - 5 + (rand() % 25);
    y = yA - 5 + (rand() % 25);
    lifetime = rand() % 6;
    particleScreen = Image::loadImage(particleSprite);
}

void Particle::show(){
    // Apply surface and age particle
    Image::applySurface(x, y, particleScreen, gameScreen);
    ++lifetime;
}

bool Particle::isDead(){
    if(lifetime > 11)
        return true;
    return false;
}

// The emitter class stuff

Emitter::Emitter(int amount, int x, int y, string particleImage, string emitterImage){
    // Seed the time for random emitter
    srand(SDL_GetTicks());
    // Set up the variables and create the particles
    x = y = xVel = yVel = 0;
    particles.resize(amount, Particle(x, y, particleImage));
    emitterScreen = Image::loadImage(emitterImage);
    particleImg = particleImage;
}

Emitter::~Emitter(){
    particles.clear();
}

void Emitter::move(){
}

void Emitter::show(){
    // Show the dot image.
    Image::applySurface(x, y, emitterScreen, gameScreen);
}

void Emitter::showParticles(){
    // Go through all the particles
    for(vector<Particle>::size_type i = 0; i != particles.size(); i++){
        if(particles[i].isDead() == true){
            particles.erase(particles.begin() + i);
            particles.insert(particles.begin() + i, Particle(x, y, particleImg));
        }
    }
    // And show all the particles
    for(vector<Particle>::size_type i = 0; i != particles.size(); i++){
        particles[i].show();
    }
}

Also here is the Splash Classand the Splash Header.

这里还有Splash Class和Splash Header。

回答by Jonathan Henson

The second option should work, and I would start looking at compilation errors to see why it doesn't. In fact, please post any compilation errors you have related to this code.

第二个选项应该有效，我将开始查看编译错误以了解为什么它不起作用。事实上，请发布与此代码相关的任何编译错误。

In the meantime, you can do something like this:

同时，您可以执行以下操作：

class Splash{
   private:
     Emitter* ps;
   public:
     Splash() { ps = new Emitter(100,200,400); }
     Splash(const Splash& copy_from_me) { //you are now responsible for this }
     Splash & operator= (const Splash & other) { //you are now responsible for this}

     ~Splash() { delete ps; }

};

回答by Rivasa

Well, I managed to fix it, in a hackish way though. What I did was create a default constructor, and move my normal Constructor code into a new function. Then I created the object and called the the new init function to set everything up.

好吧，我设法以一种骇人听闻的方式修复了它。我所做的是创建一个默认构造函数，并将我的普通构造函数代码移动到一个新函数中。然后我创建了对象并调用了新的 init 函数来设置一切。