如何制作“杂色”字体？矢量类 [英] How to make a "variadic" vector like class
问题描述
我正在尝试制作充当多维向量的类。它不需要做任何花哨的事情。我基本上想拥有一个容器类foo，我可以在其中通过foo [x] [y] [z]访问元素。现在，我还需要foo [x] [y]和foo [x]的类似类。这使我思考以下（更一般的）问题，是否有办法进行这样的事情：您可以针对任意n个参数将其初始化为foo A（a，b，c，...）并获取一个n维向量，其元素可通过[] [] [] ...访问？在类的下面，例如（四维的情况）。
I am trying to make class that acts as multidimensional vector. It doesn't have to do anything fancy. I basically want to have a "container" class foo where I can access elements by foo[x][y][z]. Now I would also need similar classes for foo[x][y] and foo[x]. Which lead me to ponder about the following (more general) question, is there a way to make something like this where you can just initialize as foo A(a,b,c,...) for any n number of arguments and get a n-dimensional vector with elements accessible by [][][]...? Below the class I have for (in example) the four-dimensional case.
首先是标题
#ifndef FCONTAINER_H
#define FCONTAINER_H
#include <iostream>
using namespace std;
class Fcontainer
{
private:
unsigned dim1, dim2, dim3, dim4 ;
double* data;
public:
Fcontainer(unsigned const dims1, unsigned const dims2, unsigned const dims3, unsigned const dims4);
~Fcontainer();
Fcontainer(const Fcontainer& m);
Fcontainer& operator= (const Fcontainer& m);
double& operator() (unsigned const dim1, unsigned const dim2, unsigned const dim3, unsigned const dim4);
double const& operator() (unsigned const dim1, unsigned const dim2, unsigned const dim3, unsigned const dim4) const;
};
#endif // FCONTAINER_H
现在的cpp：
#include "fcontainer.hpp"
Fcontainer::Fcontainer(unsigned const dims1, unsigned const dims2, unsigned const dims3, unsigned const dims4)
{
dim1 = dims1; dim2 = dims2; dim3 = dims3; dim4 = dims4;
if (dims1 == 0 || dims2 == 0 || dims3 == 0 || dims4 == 0)
throw std::invalid_argument("Container constructor has 0 size");
data = new double[dims1 * dims2 * dims3 * dims4];
}
Fcontainer::~Fcontainer()
{
delete[] data;
}
double& Fcontainer::operator() (unsigned const dims1, unsigned const dims2, unsigned const dims3, unsigned const dims4)
{
if (dims1 >= dim1 || dims2 >= dim2 || dims3 >= dim3 || dims4 >= dim4)
throw std::invalid_argument("Container subscript out of bounds");
return data[dims1*dim2*dims3*dim4 + dims2*dim3*dim4 + dim3*dim4 + dims4];
}
double const& Fcontainer::operator() (unsigned const dims1, unsigned const dims2, unsigned const dims3, unsigned const dims4) const
{
if(dims1 >= dim1 || dims2 >= dim2 || dims3 >= dim3 || dims4 >= dim4)
throw std::invalid_argument("Container subscript out of bounds");
return data[dims1*dim2*dims3*dim4 + dims2*dim3*dim4 + dim3*dim4 + dims4];
}
所以我想将其扩展到任意尺寸。我想这将采用可变参数模板或std :: initializer_list的形式，但是我不清楚如何处理此问题（针对此问题）。
So I want to expand this to an arbitrary amount of dimensions. I suppose it will take something along the lines of a variadic template or an std::initializer_list but I am not clear on how to approach this( for this problem).
推荐答案
在Visual Studio中闲逛了一会儿，我想到了这个废话：
Messing around in Visual Studio for a little while, I came up with this nonsense:
template<typename T>
class Matrix {
std::vector<size_t> dimensions;
std::unique_ptr<T[]> _data;
template<typename ... Dimensions>
size_t apply_dimensions(size_t dim, Dimensions&& ... dims) {
dimensions.emplace_back(dim);
return dim * apply_dimensions(std::forward<Dimensions>(dims)...);
}
size_t apply_dimensions(size_t dim) {
dimensions.emplace_back(dim);
return dim;
}
public:
Matrix(std::vector<size_t> dims) : dimensions(std::move(dims)) {
size_t size = flat_size();
_data = std::make_unique<T[]>(size);
}
template<typename ... Dimensions>
Matrix(size_t dim, Dimensions&&... dims) {
size_t size = apply_dimensions(dim, std::forward<Dimensions>(dims)...);
_data = std::make_unique<T[]>(size);
}
T & operator()(std::vector<size_t> const& indexes) {
if(indexes.size() != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
return _data[get_flat_index(indexes)];
}
T const& operator()(std::vector<size_t> const& indexes) const {
if (indexes.size() != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
return _data[get_flat_index(indexes)];
}
template<typename ... Indexes>
T & operator()(size_t idx, Indexes&& ... indexes) {
if (sizeof...(indexes)+1 != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
size_t flat_index = get_flat_index(0, idx, std::forward<Indexes>(indexes)...);
return at(flat_index);
}
template<typename ... Indexes>
T const& operator()(size_t idx, Indexes&& ... indexes) const {
if (sizeof...(indexes)+1 != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
size_t flat_index = get_flat_index(0, idx, std::forward<Indexes>(indexes)...);
return at(flat_index);
}
T & at(size_t flat_index) {
return _data[flat_index];
}
T const& at(size_t flat_index) const {
return _data[flat_index];
}
size_t dimension_size(size_t dim) const {
return dimensions[dim];
}
size_t num_of_dimensions() const {
return dimensions.size();
}
size_t flat_size() const {
size_t size = 1;
for (size_t dim : dimensions)
size *= dim;
return size;
}
private:
size_t get_flat_index(std::vector<size_t> const& indexes) const {
size_t dim = 0;
size_t flat_index = 0;
for (size_t index : indexes) {
flat_index += get_offset(index, dim++);
}
return flat_index;
}
template<typename ... Indexes>
size_t get_flat_index(size_t dim, size_t index, Indexes&& ... indexes) const {
return get_offset(index, dim) + get_flat_index(dim + 1, std::forward<Indexes>(indexes)...);
}
size_t get_flat_index(size_t dim, size_t index) const {
return get_offset(index, dim);
}
size_t get_offset(size_t index, size_t dim) const {
if (index >= dimensions[dim])
throw std::runtime_error("Index out of Bounds");
for (size_t i = dim + 1; i < dimensions.size(); i++) {
index *= dimensions[i];
}
return index;
}
};
让我们来谈谈这段代码是做什么的。
Let's talk about what this code accomplishes.
//private:
template<typename ... Dimensions>
size_t apply_dimensions(size_t dim, Dimensions&& ... dims) {
dimensions.emplace_back(dim);
return dim * apply_dimensions(std::forward<Dimensions>(dims)...);
}
size_t apply_dimensions(size_t dim) {
dimensions.emplace_back(dim);
return dim;
}
public:
Matrix(std::vector<size_t> dims) : dimensions(std::move(dims)) {
size_t size = flat_size();
_data = std::make_unique<T[]>(size);
}
template<typename ... Dimensions>
Matrix(size_t dim, Dimensions&&... dims) {
size_t size = apply_dimensions(dim, std::forward<Dimensions>(dims)...);
_data = std::make_unique<T[]>(size);
}
此代码使我们能够执行的操作是为该矩阵编写一个初始化器，该初始化器需要任意数量的
What this code enables us to do is write an initializer for this matrix that takes an arbitrary number of dimensions.
int main() {
Matrix<int> mat{2, 2}; //Yields a 2x2 2D Rectangular Matrix
mat = Matrix<int>{4, 6, 5};//mat is now a 4x6x5 3D Rectangular Matrix
mat = Matrix<int>{9};//mat is now a 9-length 1D array.
mat = Matrix<int>{2, 3, 4, 5, 6, 7, 8, 9};//Why would you do this? (yet it compiles...)
}
如果仅知道尺寸的数量和大小在运行时，此代码将解决以下问题：
And if the number and sizes of the dimensions is only known at runtime, this code will work around that:
int main() {
std::cout << "Input the sizes of each of the dimensions.\n";
std::string line;
std::getline(std::cin, line);
std::stringstream ss(line);
size_t dim;
std::vector<size_t> dimensions;
while(ss >> dim)
dimensions.emplace_back(dim);
Matrix<int> mat{dimensions};//Voila.
}
然后，我们希望能够访问此矩阵的任意索引。这段代码提供了两种方法：静态使用模板，或在运行时可变。
Then, we want to be able to access arbitrary indexes of this matrix. This code offers two ways to do so: either statically using templates, or variably at runtime.
//public:
T & operator()(std::vector<size_t> const& indexes) {
if(indexes.size() != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
return _data[get_flat_index(indexes)];
}
T const& operator()(std::vector<size_t> const& indexes) const {
if (indexes.size() != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
return _data[get_flat_index(indexes)];
}
template<typename ... Indexes>
T & operator()(size_t idx, Indexes&& ... indexes) {
if (sizeof...(indexes)+1 != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
size_t flat_index = get_flat_index(0, idx, std::forward<Indexes>(indexes)...);
return at(flat_index);
}
template<typename ... Indexes>
T const& operator()(size_t idx, Indexes&& ... indexes) const {
if (sizeof...(indexes)+1 != dimensions.size())
throw std::runtime_error("Incorrect number of parameters used to retrieve Matrix Data!");
size_t flat_index = get_flat_index(0, idx, std::forward<Indexes>(indexes)...);
return at(flat_index);
}
然后，在实践中：
Matrix<int> mat{6, 5};
mat(5, 2) = 17;
//mat(5, 1, 7) = 24; //throws exception at runtime because of wrong number of dimensions.
mat = Matrix<int>{9, 2, 8};
mat(5, 1, 7) = 24;
//mat(5, 2) = 17; //throws exception at runtime because of wrong number of dimensions.
这在运行时动态索引中很好用：
And this works fine with runtime-dynamic indexing:
std::vector<size_t> indexes;
/*...*/
mat(indexes) = 54; //Will throw if index count is wrong, will succeed otherwise
此类对象还有许多其他功能可能想像 resize 方法一样，但是选择如何实现它是一个高级设计决策。我还遗漏了大量其他可能有价值的实现细节（例如优化的移动构造函数，比较运算符，复制构造函数），但这应该使您对如何开始有了一个很好的了解。
There are a number of other functions that this kind of object might want, like a resize method, but choosing how to implement that is a high-level design decision. I've also left out tons of other potentially valuable implementation details (like an optimizing move-constructor, a comparison operator, a copy constructor) but this should give you a pretty good idea of how to start.
如果您想完全避免使用模板，则可以将此处提供的代码削减一半，而只需使用使用<$ c的方法/构造函数即可。 $ c> std :: vector< size_t> 提供尺寸/索引数据。如果您不需要在运行时动态适应尺寸数量的功能，则可以删除 std :: vector< size_t> 重载，甚至可以使类本身的模板参数的维数（这将使您可以使用 size_t [] 或 std :: array [size_t，N] 来存储维度数据。
If you want to avoid use of templates entirely, you can cut like half of the code provided here, and just use the methods/constructor that uses std::vector<size_t> to provide dimensions/index data. If you don't need the ability to dynamically adapt at runtime to the number of dimensions, you can remove the std::vector<size_t> overloads, and possibly even make the number of dimensions a template argument for the class itself (which would enable you to use size_t[] or std::array[size_t, N] to store dimensional data).
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