模板类构造函数问题 - 设计多字节数组的容器 [英] Template class constructor issues - designing a container for multidim arrays

问题描述

我想为数值计算的任何维度的数组创建自己的容器。我想使用模板，这样我可以重载下标运算符[]，使其工作原理类似于正常的数组和向量。访问条目像[10] [10] [10]等。

I'm trying to create my own container for an array of any dimension for numerical computing. I would like to do this using templates so that I could overload the subscript operator [] so that it works like normal arrays and vectors e.g. access entries like a[10][10][10] etc.

当尝试创建容器以保持多维数组时，我无法使构造函数工作。请帮助！

I am having trouble getting the constructor to work when trying to create containers to hold multidimensional arrays. Please help!

#include <iostream>
#include <iterator>
#include <algorithm>
#include <vector>
using namespace std;

template <class T>
class container{
public:
 inline T& operator[](int i){return data[i];}
 container(int si, T initval){
  size=si; 
  data=new T[size]; 
  transform(data,data+size,data, [initval] (T d) {return initval;});
        // transform fills array with the initial value. 
 }
 ~container(){delete [] data;}
private:
 T* data;
 int size;
};

int main(){
 //For example:
 vector<vector<int>> v1(10,vector<int>(10,0)); //2D 10x10
 vector<vector<vector<int>>> v2(10,vector<vector<int>>(10,vector<int>(10,0))); 
    //3D 10x10x10

 container<int> c1(10,0); //1D 10x1 works!
 container<container<int>> c2(10,container<int>(10,0)); //2D 10x10 fails!

 system("pause");
 return 0;
}

VS10错误输出：

error C2512: 'container<T>' : no appropriate default constructor available

      with
      [
          T=int
      ]
      c:\users\jack\documents\visual studio 2010\projects\ref\ref\ref.cpp(11) : while compiling class template member function 'container<T>::container(int,T)'
      with
      [
          T=container<int>
      ]
      c:\users\jack\documents\visual studio 2010\projects\ref\ref\ref.cpp(28) : see reference to class template instantiation 'container<T>' being compiled
      with
      [
          T=container<int>
      ]

Build FAILED.

我知道我可以使用valarray或boost库，但我想了解如何创建我自己的。效率很重要。感谢！

I know I could just use valarray or a boost library, but I would like to understand how to create my own. Efficiency is important. Thanks!

推荐答案

您的构造函数使用表达式 new T [size] 并且这需要 T 是默认可构造的（如果 T 是类类型）。

Your constructor uses the expression new T[size] and this requires T to be default constructible (if T is a class type).

你需要做一些事情：分配原始内存（例如使用 operator new ）并构造 T 使用展示位置 new 表达式in place。或者，您可以给 container 一个默认构造函数。

You need to do something like: allocate raw memory (e.g. using operator new) and construct T instances "in place" using a placement new expression. Alternatively, you could just give container a default constructor.

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