在c ++中将多维数组转换为指针 [英] Converting multidimensional arrays to pointers in c++

问题描述

我有一个如下所示的程序：

  double [4] [4] startMatrix; 
 double [4] [4] inverseMatrix; 
 initialize（startMatrix）//这将我想要的信息放在startMatrix中
  

以计算startMatrix的逆，并将其放入inverseMatrix。我有一个库函数为此目的，其原型如下：

  void MatrixInversion（double ** A，int order，double ** B）
  

取得A的倒数并将其放入B.问题是需要知道如何将double [4] [4]转换为double **来赋予函数。我试过只是做明显的方式：

  MatrixInversion（（double **）startMatrix，4， **）inverseMatrix））
  

但这似乎不工作。这是真正的方法吗？

解决方案

不，没有正确的方法做到这一点。 double [4] [4] 数组不能转换为 double ** 指针。这是两种替代的，不兼容的方式来实现2D阵列。需要改变的东西：函数的接口，或作为参数传递的数组的结构。

最简单的方法做后者， double [4] [4] 数组兼容该函数，是创建临时索引数组类型 double * [4] 指向每个矩阵中每行的开始

  double * startRows [4] = {startMatrix [0] ，startMatrix [1]，startMatrix [2]，startMatrix [3]}; 
 double * inverseRows [4] = {/ * same thing here * /}; 
 

并传递这些索引数组

  MatrixInversion（startRows，4，inverseRows）; 
  

一旦函数完成工作，就可以忘记 startRows 和 inverseRows 数组，因为结果将被正确放入原始的 inverseMatrix 数组。 >


I have a program that looks like the following:

double[4][4] startMatrix;
double[4][4] inverseMatrix;
initialize(startMatrix) //this puts the information I want in startMatrix

I now want to calculate the inverse of startMatrix and put it into inverseMatrix. I have a library function for this purpose whose prototype is the following:

void MatrixInversion(double** A, int order, double** B)

that takes the inverse of A and puts it in B. The problem is that I need to know how to convert the double[4][4] into a double** to give to the function. I've tried just doing it the "obvious way":

MatrixInversion((double**)startMatrix, 4, (double**)inverseMatrix))

but that doesn't seem to work. Is that actually the right way to do it?

解决方案

No, there's no right way to do specifically that. A double[4][4] array is not convertible to a double ** pointer. These are two alternative, incompatible ways to implement a 2D array. Something needs to be changed: either the function's interface, or the structure of the array passed as an argument.

The simplest way to do the latter, i.e. to make your existing double[4][4] array compatible with the function, is to create temporary "index" arrays of type double *[4] pointing to the beginnings of each row in each matrix

double *startRows[4] = { startMatrix[0], startMatrix[1], startMatrix[2] , startMatrix[3] };
double *inverseRows[4] = { /* same thing here */ };

and pass these "index" arrays instead

MatrixInversion(startRows, 4, inverseRows);

Once the function finished working, you can forget about the startRows and inverseRows arrays, since the result will be placed into your original inverseMatrix array correctly.

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