使用指针数组作为参数传递给方法 [英] Using array of pointers as parameter to method

问题描述

我必须使用指针数组对象，我也必须把它作为参数的方法。然而，要做到这一点的方式逃避我。这里是我使用的数组的元素的初始化的方法。当我提领他们在主，他们的数据是不正确的（它们包含的内存地址）。什么是正确的方法是什么？也许它是假的方式提领我他们？

I have to use an array of pointers to Objects and I must also pass it as parameter to methods. However the way to do this eludes me. Here is the method I use for the initialization of the elements of the array. When I dereference them in main, their data are not correct (they contain memory addresses). What is the correct way? Might it be false the way I dereference them?

void createSquares(Square* squareArray[]){

    PropertySquare PropertySquare1(1,"purple",120);
    PropertySquare PropertySquare2(2,"purple",170);

    squareArray[1] = &PropertySquare1;
    squareArray[2] = &PropertySquare2;
.
.
.
}

在主要的：

Square *allSquares[22] ;
createSquares(allSquares);

cout<<"ID is: "<<allSquares[1]->getID()<<endl;
cin.get();

正如我所说的ID是终于内存地址。

As I said the ID is finally a memory address.

更新基于答案：

我已经试过这一点，它不工作作为well.It当务之急是我使用多态。

I have tried this and it does not work as well.It is imperative for me to use polymorphism.

vector<Square*> allSquares;
createSquares(allSquares);

void createSquares(vector<Square*> &squares){

PropertySquare PropertySquare1(1,"purple",120);
PropertySquare PropertySquare2(2,"purple",170);

squares.push_back(&PropertySquare1);
squares.push_back(&PropertySquare2);

}

在主：

for (vector<Square*>::iterator it=allSquares.begin(); it!=allSquares.end();it++){
   it->
}

它不允许我使用广场的虚函数，因为它是抽象的。
任何建议？

It does not allow me to use the virtual functions of Square since it is abstract. Any suggestion?

推荐答案

你做的一切都是不好的。这是棘手弄清楚哪里开始，所以让我开始在年底和present正确方法：

Everything you're doing is Not Good. It's tricky to figure out where to begin, so let me start at the end and present The Right Way:

typedef std::unique_ptr<Square> square_ptr;

void createSquares(std::vector<square_ptr> & v)
{
  v.emplace_back(new PropertySquare1(1,"purple",120));
  v.emplace_back(new PropertySquare1(2,"green",370));
  // ...
}

int main()
{
  std::vector<square_ptr> allSquares;
  createSquares(allSquares);

  for (const auto & p : allSquares)
    std::cout << "ID is: " << p->getID() << std::endl;
}

---

现在打破你的问题：

---

Now to break down your problems:

首先，你要存储局部变量的指针。这些局部变量死在函数范围的结束，指针变成晃来晃去。解引用是程序错误。

First off, you are storing the pointers of local variables. Those local variables die at the end of the function scope, and the pointers become dangling. Dereferencing is a program error.

第二，要解决这个问题，您应该创建的动态的对象： squareArray [1] =新PropertySquare1（1，紫，120）; 然而，这是有问题的，也。有人会来清理这些对象！你可以遍历每个元素的数组，并调用删除。

Second, to fix this, you should create dynamic objects: squareArray[1] = new PropertySquare1(1,"purple",120); However, that is problematic, too. Someone will have to clean up those objects! You could iterate over the array and call delete on each element.

三， 22 是一个幻数（因为它既不 0 也不 1 ）。这不应该是硬codeD。如果数字真的是一个编译时间常数，地方的名字。

Third, 22 is a "magic number" (because it's neither 0 nor 1). This should not be hard-coded. If the number really is a compile-time constant, name it somewhere.

第四，无论哪种方式，不使用原始数组。无论是使用的std ::阵列如果大小在编译时已知或的std ::矢量如果的大小是在运行时确定的。

Fourth, either way, don't use raw arrays. Either use a std::array if the size is known at compile-time, or a std::vector if the size is determined at runtime.

第五，把他们放在一起，智能指针的动态容器照顾您所有的后顾之忧。这是在我的code psented一个$ P $。另一种选择，智能指针的静态数组，不会使用一个初始化函数所有，而是要正确当场进行初始化：

Fifth, putting it all together, a dynamic container of smart pointers takes care of all your worries. That's the one presented in my code. The alternative, a static array of smart pointers, wouldn't use an initialization function at all, but rather it'd be initialized right on the spot:

const std::size_t nfuncs = 22;
std::array<square_ptr, nfuncs> allSquares {
  new PropertySquare1(1,"purple",120),
  new PropertySquare1(2,"green",370),
  // ...
};

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