指向多维数组的指针 [英] Pointers to multiple dimension arrays

问题描述

我有2个数组，分别是int a [10] [20]和int b [10] [20].我想为一个或另一个数组创建一个点并读取数据.在一种情况下，我可能需要数据，而在另一种情况下，我可能需要b数据.

I have 2 arrays, int a[10][20] and int b[10][20]. I want to create a point to one or the other array and read the data. In one condition I may want a data and the other I might want b data.

示例.

int ** ptr;

int **ptr;

ptr =& a;  //不起作用，无法找出如何为现有二维数组分配指针

ptr=&a;  // doesn''t work can''t figure out how to assign a pointer to and existing 2 dimension array

推荐答案

在C ++中指向多维​​数组的指针很棘手.通常，您必须指定每个维度的实际容量，这意味着一个指针不能用于两个不同大小的数组.如果您真的想要一个指针，我建议您制作一个单一维度的数组，然后就可以计算索引以使用多个维度.会像这样:

Pointers to multidimensional arrays in C++ is tricky business. Most often, you have to specify the actual capacity of each dimension, which means one pointer cannot be used for two different sized arrays. If you really want a pointer, I suggest making a single dimension array and then you can just calculate the index to use multiple dimensions. Would go something like this:

int wide = 640; int tall = 480;
int * pArray = new int[wide * tall];
int x; int y; int yOffset; int offset;
for(y = 0; y < tall; y++)
{
	yOffset = y * wide;
	for(x = 0; x < wide; x++)
	{
		offset = yOffset + x;
		// Use pointer arithmetic to assign element at (x,y).
		*(pArray + offset) = CalculateSomething(x, y);
	}
}

好吧，它们要么是相同的数组，要么是两个不同的数组.您可以编写一个类来交换它查找的指针，但是不能有两个数组也都是相同的数组，但有时是这样.

Well, they are either the same array, or two different arrays.  You could write a class that swaps which pointer it looks up, but you can''t have two arrays that are also the same array, but only sometimes.

好吧，我尝试过，但是我完全困惑为什么它不起作用(请注意奇怪的错误，在其所在行上方的注释中):

Well, I tried, but I''m completely baffled as to why this doesn''t work (note the strange error, which is in a comment above the line it occurs at):

// Interface to access array functions (get value, set value).
template<class T>
class IArrayHolder{
public:
	virtual T GetVal(int x, int y) = 0;
	//...Set value...
};

// Class to wrap an array.
template<class T, class S>
class ArrayHolder: public IArrayHolder<S>
{
private:
	T multiArray;
public:
	ArrayHolder(T val){
		// error C2440: '=' : cannot convert from 'int [][20]' to 'int [][20]'
		multiArray = val;
	}
	S GetVal(int x, int y){
		return multiArray[x][y];
	};
};

// Some function that uses multiple multi-dimension arrays.
System::Void SomeFunction(){
	int x[10][20];
	int y[20][30];
	IArrayHolder<int> * xInterface;
	xInterface = new ArrayHolder<int[][20], int>(x);
	IArrayHolder<int> * yInterface;
	yInterface = new ArrayHolder<int[][30], int>(y);
};

// Some function that accepts a 2D array.
System::Void AnotherFunction(IArrayHolder<int> * arrayHolder){
	int val = arrayHolder->GetVal(20, 20);
};

您找出该错误，然后就可以解决了.如果不是这样，也许您应该只将数组值复制到2D向量中，然后使用它.另外，我对void指针没有太多的经验，但是它们显然可以指向任何对象的地址，因此您可以尝试使用它们.

You figure out that error, and you''ve go your solution. If not, perhaps you should just copy the array values to a 2D vector and use that instead. Also, I don''t have much experience with void pointers, but they can apparently point to the address of anything, so you might try working with those.

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