我如何最好地处理 C/C++ 中的动态多维数组? [英] How do I best handle dynamic multi-dimensional arrays in C/C++?
问题描述
在 C 和/或 C++ 中操作动态(所有维度直到运行时都不知道)多维数组的公认/最常用方法是什么.
What is the accepted/most commonly used way to manipulate dynamic (with all dimensions not known until runtime) multi-dimensional arrays in C and/or C++.
我试图找到最简洁的方式来完成这段 Java 代码的工作:
I'm trying to find the cleanest way to accomplish what this Java code does:
public static void main(String[] args){
Scanner sc=new Scanner(System.in);
int rows=sc.nextInt();
int cols=sc.nextInt();
int[][] data=new int[rows][cols];
manipulate(data);
}
public static void manipulate(int[][] data){
for(int i=0;i<data.length;i++)
for(int j=0;j<data[0].length.j++){
System.out.print(data[i][j]);
}
}
(从 std_in 读取只是为了说明尺寸直到运行时才知道).
(reads from std_in just to clarify that dimensions aren't known until runtime).
我注意到这个问题很受欢迎，尽管它已经很老了.我实际上并不同意最高投票的答案.我认为 C 的最佳选择是使用一维数组，正如 Guge 在下面所说的您可以分配行 colssizeof(int) 并通过 table[row*cols+col] 访问它.".
I noticed that this question is pretty popular even though it's pretty old. I don't actually agree with the top voted answer. I think the best choice for C is to use a single-dimensional array as Guge said below "You can alloc rowscolssizeof(int) and access it by table[row*cols+col].".
C++ 有很多选择，如果您真的喜欢 boost 或 stl，那么下面的答案可能更可取，但最简单且可能最快的选择是使用 C 中的一维数组.
There is a number of choices with C++, if you really like boost or stl then the answers below might be preferable, but the simplest and probably fastest choice is to use a single dimensional array as in C.
如果您想要 [][] 语法，C 和 C++ 中的另一个可行选择是底部的 lillq 答案是手动构建具有大量 malloc 的数组.
Another viable choice in C and C++ if you want the [][] syntax is lillq's answer down at the bottom is manually building the array with lots of malloc's.
推荐答案
Use boost::multi_array.
在您的示例中，您在编译时唯一需要知道的是维数.这是文档中的第一个示例:
As in your example, the only thing you need to know at compile time is the number of dimensions. Here is the first example in the documentation :
#include "boost/multi_array.hpp"
#include <cassert>
int
main () {
// Create a 3D array that is 3 x 4 x 2
typedef boost::multi_array<double, 3> array_type;
typedef array_type::index index;
array_type A(boost::extents[3][4][2]);
// Assign values to the elements
int values = 0;
for(index i = 0; i != 3; ++i)
for(index j = 0; j != 4; ++j)
for(index k = 0; k != 2; ++k)
A[i][j][k] = values++;
// Verify values
int verify = 0;
for(index i = 0; i != 3; ++i)
for(index j = 0; j != 4; ++j)
for(index k = 0; k != 2; ++k)
assert(A[i][j][k] == verify++);
return 0;
}
正如评论中所建议的，这里是一个简单"示例允许您在运行时定义多维数组大小，从控制台输入询问.这是此示例应用程序的示例输出(使用常量表示它是 3 维编译):
As suggested in the comments, here is a "simple" example application that let you define the multi-dimensional array size at runtime, asking from the console input. Here is an example output of this example application (compiled with the constant saying it's 3 dimensions) :
Multi-Array test!
Please enter the size of the dimension 0 : 4
Please enter the size of the dimension 1 : 6
Please enter the size of the dimension 2 : 2
Text matrix with 3 dimensions of size (4,6,2) have been created.
Ready!
Type 'help' for the command list.
>read 0.0.0
Text at (0,0,0) :
""
>write 0.0.0 "This is a nice test!"
Text "This is a nice test!" written at position (0,0,0)
>read 0.0.0
Text at (0,0,0) :
"This is a nice test!"
>write 0,0,1 "What a nice day!"
Text "What a nice day!" written at position (0,0,1)
>read 0.0.0
Text at (0,0,0) :
"This is a nice test!"
>read 0.0.1
Text at (0,0,1) :
"What a nice day!"
>write 3,5,1 "This is the last text!"
Text "This is the last text!" written at position (3,5,1)
>read 3,5,1
Text at (3,5,1) :
"This is the last text!"
>exit
代码中的重要部分是我们从用户那里获取维度并使用以下命令创建数组的主要功能:
The important parts in the code are the main function where we get the dimensions from the user and create the array with :
const unsigned int DIMENSION_COUNT = 3; // dimension count for this test application, change it at will :)
// here is the type of the multi-dimensional (DIMENSION_COUNT dimensions here) array we want to use
// for this example, it own texts
typedef boost::multi_array< std::string , DIMENSION_COUNT > TextMatrix;
// this provide size/index based position for a TextMatrix entry.
typedef std::tr1::array<TextMatrix::index, DIMENSION_COUNT> Position; // note that it can be a boost::array or a simple array
/* This function will allow the user to manipulate the created array
by managing it's commands.
Returns true if the exit command have been called.
*/
bool process_command( const std::string& entry, TextMatrix& text_matrix );
/* Print the position values in the standard output. */
void display_position( const Position& position );
int main()
{
std::cout << "Multi-Array test!" << std::endl;
// get the dimension informations from the user
Position dimensions; // this array will hold the size of each dimension
for( int dimension_idx = 0; dimension_idx < DIMENSION_COUNT; ++dimension_idx )
{
std::cout << "Please enter the size of the dimension "<< dimension_idx <<" : ";
// note that here we should check the type of the entry, but it's a simple example so lets assume we take good numbers
std::cin >> dimensions[dimension_idx];
std::cout << std::endl;
}
// now create the multi-dimensional array with the previously collected informations
TextMatrix text_matrix( dimensions );
std::cout << "Text matrix with " << DIMENSION_COUNT << " dimensions of size ";
display_position( dimensions );
std::cout << " have been created."<< std::endl;
std::cout << std::endl;
std::cout << "Ready!" << std::endl;
std::cout << "Type 'help' for the command list." << std::endl;
std::cin.sync();
// we can now play with it as long as we want
bool wants_to_exit = false;
while( !wants_to_exit )
{
std::cout << std::endl << ">" ;
std::tr1::array< char, 256 > entry_buffer;
std::cin.getline(entry_buffer.data(), entry_buffer.size());
const std::string entry( entry_buffer.data() );
wants_to_exit = process_command( entry, text_matrix );
}
return 0;
}
你可以看到，要加入数组中的一个元素，真的很简单:你只需要像下面的函数一样使用 operator() :
And you can see that to accede an element in the array, it's really easy : you just use the operator() as in the following functions :
void write_in_text_matrix( TextMatrix& text_matrix, const Position& position, const std::string& text )
{
text_matrix( position ) = text;
std::cout << "Text \"" << text << "\" written at position ";
display_position( position );
std::cout << std::endl;
}
void read_from_text_matrix( const TextMatrix& text_matrix, const Position& position )
{
const std::string& text = text_matrix( position );
std::cout << "Text at ";
display_position(position);
std::cout << " : "<< std::endl;
std::cout << " \"" << text << "\"" << std::endl;
}
注意:我在 VC9 + SP1 中编译了这个应用程序 - 只有一些容易忘记的警告.
Note : I compiled this application in VC9 + SP1 - got just some forgettable warnings.
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