如何使用构造函数在另一个类中创建一个对象？ [英] How to create an object inside another class with a constructor?

问题描述

所以我正在编写我的代码，它是以模块化的方式设计的。现在，我的一个班;调用 Splash 必须创建另一个类的对象，名为 Emitter 。通常，你只需创建对象，并使用它，但这不工作在这里，因为 Emitter 类有一个自定义构造函数。

So I was working on my code, which is designed in a modular way. Now, one of my classes; called Splash has 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 Emitter class has a custom constructor. But when I try to create an object, it doesn't work.

例如：

我试图这样做， t work：

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

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

我也试过这个，也没有工作：

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

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

编辑：我知道第二种方式工作，然而它不。如果我删除 Emitter 节，代码工作。但是当我以第二种方式，没有窗口打开，没有应用程序被执行。

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

那么如何创建我的发射器

编辑：

这是我的代码为发射器类和头：
头

Here is my code for the emitter class and header: 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

这里是发射器功能：

#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();
    }
}

这里还有 Splash类和 Splash标题。

推荐答案

第二个选项应该工作，我会开始看编译错误，看看为什么没有。事实上，请发布任何与此代码相关的编译错误。

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.

在此期间，您可以这样做：

In the meantime, you can do something like this:

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; }

};

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