如何创建一个特定类的boost多数组

Question

这是我第一次使用Boost，我试图创建类块的多数组，它存储在类Chunk中。所以每个Chunk由(BLOCKS_PER_CHUNK x BLOCKS_PER_CHUNK x BLOCKS_PER_CHUNK)数量的block组成，本质上与Minecraft的方式相同。目前，我正在尝试使用两个不同的构造函数初始化这个数组，一个将stl向量作为输入，另一个使用"C风格向量"。

Block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Block类型(基本上是一个enum)以及变量的getter和setter。

Chunk的报头如下:

#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) ];
            }
        }
    }
} 

在尝试编译这段代码时，我收到错误，例如shape, num_dimensions, begin和end不是Block的成员。boost似乎有自己的静态断言风格，它检查必需的字段，当没有找到这些字段时，它会创建编译错误。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(例如两个"子数组"具有相同的维数)时，它会触发错误。

容器的手册似乎没有解决这个特定的问题，我不相信我意外地创建了一个多数组视图。另外，将左侧的索引转换为boost::multi_array<Block, BLOCKS_PER_CHUNK>::index似乎没有产生任何差异。正如我所提到的，我仍然是一个新手。正确的方法是什么呢?

Answer 1

m_blocks初始化时出现错误。您指定BLOCKS_PER_CHUNK值为16，但只将其初始化为三维数组。

#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;
}

上面的例子编译正确，因为BLOCKS_PER_CHUNK和m_blocks初始化匹配。例如，BLOCKS_PER_CHUNK定义为4，那么m_blocks应该初始化为:

  #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，16深的块集合，那么代码应该像这样:

  #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 typepedef中的第二个参数指定了数组的维度，如果你想要它是3，那么typedef应该修改为:

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