初始化在C的二维对象数组++ [英] Initializing a two-dimensional object array in c++

问题描述

我知道这之前已经被要求（或一些类似的变化），但是我不能得到它的工作。

I know this has been asked before (or some similar variations) however I cannot get it to work.

我想创建一个由充满正方形板的棋盘游戏。我想我的主板型号为广场对象的二维数组。该板可与任何宽度或高度被创建，这些参数是通过构造函数传递。这里是code我一起工作：

I am trying to create a board game that is composed of a board filled with squares. I am trying to model my board as a 2d array of Square objects. The board can be created with any width or height, and those parameters are passed in through the constructor. Here is the code I am working with:

Board.h

#ifndef BOARD_H
#define BOARD_H

#include "Square.h"

class Board{
public:
    Board(int w, int h);

private:
    Square **squares;
    const int width;
    const int height;
};

#endif

Board.cpp

#include "Board.h"

Board::Board(int w, int h):width(w), height(h) {
    squares = new Square*[width];

    for (int i = 0; i < width; i++) {
        squares[i] = new Square[height];
    }
}

然而，当我尝试编译此，我得到这似乎预示着平方错误[I] =新广场[高度] 试图调用默认的构造函数为方形对象（我不想存在也不在这种情况下，调用）。

However, when I try to compile this I get an error which seems to indicate the squares[i] = new Square[height] is trying to call the default constructor for the Square object (which I do not want to exist nor call in this case).

Board.cpp: In constructor ‘Board::Board(int, int)’:
Board.cpp:7:33: error: no matching function for call to ‘Square::Square()’
   squares[i] = new Square[height];

任何想法？这是可能的范围内C ++？

Any ideas? Is this possible within C++?

推荐答案

您code是相同的：

struct Foo
{
    Foo(int){} // no default constructor
    // Foo() = default; /* uncomment this and it will work */
};

int main()
{
    Foo* pFoo = new Foo[10]; // need a default ctor
    delete[] pFoo;
}   

问题是，在美孚* PFOO =新富的RHS [10]; ，你是分配内存的以及创建 10 富的对象。编译器不知道该怎么办后者（创建对象），因为你不提供一个默认的构造函数。为了使上述code工作原样，则需要指定全部作为每个对象的非默认的构造函数，如参数：

The problem is that on the rhs of Foo* pFoo = new Foo[10];, you are allocating the memory as well as creating 10 Foo objects. The compiler doesn't know how to do the latter (creating the objects), as you don't provide a default constructor. To make the above code work as is, you need to specify all arguments for the non-default ctor of each object, like:

Foo* pFoo = new Foo[10]{1,2,3,4,5,6,7,8,9,0}; // this will work

更好的替代方法是使用 STD： ：矢量 代替。如果你想知道为什么，无需后期作品没有一个默认的构造函数的对象，这是因为它使用的布局新 ，并初始化需求的元素。

The better alternative is to use std::vector instead. If you wonder why the latter works without the need for objects that don't have a default constructor, it is because it uses the placement new, and initializes the elements on demand.

这里你可以看到如何使用位置新。

Here you can see how to do it with placement new.

修改

在code

Foo* pFoo = new Foo[10]{1,2,3,4,5,6,7,8,9,0}; 

在编译GCC，但铛无法编译它（与 -std = C ++ 11 标志）。这里跟进问题。

compiles in gcc, but clang fails to compile it (with -std=c++11 flag). Follow up question here.

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