如何创建特定类的 boost 多数组？

Question

这是我第一次使用 Boost，我正在尝试创建一个 Blocks 类的多数组，该数组存储在 Chunk 类中。所以每个块由 (BLOCKS_PER_CHUNK x BLOCKS_PER_CHUNK x BLOCKS_PER_CHUNK) 个块组成，基本上与 Minecraft 相同。目前我正在尝试使用两个不同的构造函数来初始化这个数组，一个使用 stl 向量作为输入，另一个使用“C 样式向量”。

块只有一个布尔值来检查它是否处于活动状态（默认值为 false）、一个块类型（基本上是一个枚举）以及一个用于变量的 getter 和 setter。

Chunk 的头部如下：

#pragma once

#include "Block.h"
#include <vector>
#include "Block.h"
#include "boost/multi_array.hpp" // Multi dimensional array

#define BLOCKS_PER_CHUNK 16

class Chunk
{
public:
    Chunk();
    Chunk(std::vector<Block>& blocks);
    Chunk(Block* blocks); // Assumes you have a vector of the correct size
    virtual ~Chunk();

    void Update(float timeSinceLastUpdate);

private:
    //BlockVec3D blocks;
    //BlockArray blocks;
    typedef boost::multi_array<Block, BLOCKS_PER_CHUNK> blockArray;
    typedef blockArray::index blockArrayIndex;

    blockArray m_blocks;
};

问题函数如下：

Chunk::Chunk(std::vector<Block>& blocks):
    m_blocks(boost::extents[BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK])
{
    assert(blocks.size() == BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK && "Number of blocks and size of the chunk do not match");
    for(unsigned i = 0; i < BLOCKS_PER_CHUNK; ++i)
    {
        for(unsigned j = 0; j < BLOCKS_PER_CHUNK; ++j)
        {
            for( unsigned k = 0; k < BLOCKS_PER_CHUNK; ++k)
            {
                m_blocks[i][j][k] = blocks[i + BLOCKS_PER_CHUNK * (j + BLOCKS_PER_CHUNK * k) ];
            }
        }
    }
}

Chunk::Chunk(Block* blocks)
{
    for(unsigned i = 0; i < BLOCKS_PER_CHUNK; ++i)
    {
        for(unsigned j = 0; j < BLOCKS_PER_CHUNK; ++j)
        {
            for( unsigned k = 0; k < BLOCKS_PER_CHUNK; ++k)
            {
                m_blocks[i][j][k] = blocks[i + BLOCKS_PER_CHUNK * (j + BLOCKS_PER_CHUNK * k) ];
            }
        }
    }
} 

在尝试编译此代码时，我收到错误，例如 shape、num_dimensions、begin 和 end 不是 Block 的成员。似乎 boost 有自己的静态断言风格，它会检查必填字段，当找不到这些字段时，它会产生编译错误。显然，boost 试图将输入值视为一维子数组，当它无法找到其完整性检查所需的字段时（例如两个“子数组”具有相同的维数），它会触发错误。

容器的手册似乎没有解决这个特定问题，我不相信我无意中创建了一个多数组视图。此外，将左侧的索引转换为 boost::multi_array<Block, BLOCKS_PER_CHUNK>::index 似乎没有任何区别。正如我所提到的，我对提升还是很陌生。这样做的正确方法是什么？

Answer 1

错误在于 m_blocks 的初始化方式。您将 BLOCKS_PER_CHUNK 值指定为 16，但仅将其初始化为 3 维数组。

#include <iostream>
#include <vector>
#include <boost/multi_array.hpp>
#include <cassert>

#define BLOCKS_PER_CHUNK 3

struct Block{


};


struct Chunk{


  typedef boost::multi_array<Block, BLOCKS_PER_CHUNK> array_type;
  typedef array_type::index index;
  array_type m_blocks;

  Chunk(std::vector<Block>& blocks):
    m_blocks(boost::extents[BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK])
  {
    assert(blocks.size() == BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK && "Number of   
blocks and size of the chunk do not match");
    for(unsigned i = 0; i < BLOCKS_PER_CHUNK; ++i)
    {
      for(unsigned j = 0; j < BLOCKS_PER_CHUNK; ++j)
      {
for( unsigned k = 0; k < BLOCKS_PER_CHUNK; ++k)
        {
          m_blocks[i][j][k] = blocks[i + BLOCKS_PER_CHUNK * (j + BLOCKS_PER_CHUNK * k) ];
        }
      }
    }
  }

  Chunk(Block* blocks)
  {
    for(unsigned i = 0; i < BLOCKS_PER_CHUNK; ++i)
    {
      for(unsigned j = 0; j < BLOCKS_PER_CHUNK; ++j)
      {
        for( unsigned k = 0; k < BLOCKS_PER_CHUNK; ++k)
        {
          m_blocks[i][j][k] = blocks[i + BLOCKS_PER_CHUNK * (j + BLOCKS_PER_CHUNK * k) ];
        }
      }
    }
  }

};

int main(){
 return 0;
}

上面的示例编译正确，因为 BLOCKS_PER_CHUNK 和 m_blocks 初始化匹配。比如说 BLOCKS_PER_CHUNK 被定义为 4 那么 m_blocks 应该被初始化为：

  #define BLOCKS_PER_CHUNK 4

struct Block{


};


struct Chunk{

  typedef boost::multi_array<Block, BLOCKS_PER_CHUNK> array_type;
  typedef array_type::index index;
  array_type m_blocks;

  Chunk(std::vector<Block>& blocks):
//initialization has to change if BLOCKS_PER_CHUNK changes
    m_blocks(
boost::extents[BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK])
  {

    assert(blocks.size() == BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK && "Number of   blocks and size of the chunk do not match");
    for(unsigned i = 0; i < BLOCKS_PER_CHUNK; ++i)
    {
      for(unsigned j = 0; j < BLOCKS_PER_CHUNK; ++j)
      {
        for( unsigned k = 0; k < BLOCKS_PER_CHUNK; ++k)
        {
//correct value assignment has to be taken care when BLOCKS_PER_CHUNK change
          m_blocks[i][j][k][k] = blocks[i + BLOCKS_PER_CHUNK * (j + BLOCKS_PER_CHUNK * k) ];
        }
      }
    }
  }

};

如果你想要 16 宽、16 高和 16 深的块集合，那么代码应该是这样的：

  #define BLOCKS_PER_CHUNK 16
  #define DIMENSION 3

struct Block{


};


struct Chunk{

typedef boost::multi_array<Block, DIMENSION> array_type;
  typedef array_type::index index;
  array_type m_blocks;

  Chunk(std::vector<Block>& blocks):
//initialization has to change if BLOCKS_PER_CHUNK changes
    m_blocks(
boost::extents[BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK][BLOCKS_PER_CHUNK])
  {

    assert(blocks.size() == BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK * BLOCKS_PER_CHUNK && "Number of   blocks and size of the chunk do not match");
    for(unsigned i = 0; i < BLOCKS_PER_CHUNK; ++i)
    {
      for(unsigned j = 0; j < BLOCKS_PER_CHUNK; ++j)
      {
        for( unsigned k = 0; k < BLOCKS_PER_CHUNK; ++k)
        {
//correct value assignment has to be taken care when BLOCKS_PER_CHUNK change
          m_blocks[i][j][k] = blocks[i + BLOCKS_PER_CHUNK * (j + BLOCKS_PER_CHUNK * k) ];
        }
      }
    }
  }

};

array_type typedef 中的第二个参数指定数组的维度，如果你希望它是 3，那么 typedef 应该修改为：

typedef boost::multi_array<Block, DIMENSION> array_type; //where DIMENSION is 3