C++ 如何将二维数组作为参数传递？
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How to pass two-dimensional array as an argument?
提问by user543265
My Matrxclass is defined as
我的Matrx班级被定义为
class Matrx
{
double A[50][50];
int m,n;
public:
Matrx(void);
Matrx(int a, int b)
{
m=a;
n=b;
}
Matrx operator +(Matrx b);
Matrx Transpose(Matrx b);
Matrx operator *(Matrx b);
CString printMatrx();
void readMatrx(double a[][]);
Matrx TransposeMat(Matrx b);
};
void Matrx::readMatrx(double a[][])
{
for(int i=0;i< m;i++)
{
for(int j=0;j< n;j++)
A[i][j]=a[i][j];
}
}
The intellisense gives error like the below
智能感知给出如下错误
1 IntelliSense: an array may not have elements of this type d:\bmadaptive_dd_v1.02\matrx.h 17 27 TestServer
1 IntelliSense：数组可能没有这种类型的元素 d:\bmadaptive_dd_v1.02\matrx.h 17 27 TestServer
Why?
为什么？
How to pass a two dimensional array as argument of the function?
如何将二维数组作为函数的参数传递？
采纳答案by sellibitze
You need to properly learn about arrays and pointers. This includes the lesson "huh! They are not as useful as I thought they were". After you've gotten familiar with how arrays and pointers work exactly you should rethink your design.
您需要正确了解数组和指针。这包括“哈！它们没有我想象的那么有用”这一课。在您熟悉了数组和指针的工作原理之后，您应该重新考虑您的设计。
For example, in my opinion, the following design has lots of advantages:
例如，在我看来，以下设计有很多优点：
#ifndef MATRIX_HPP_INCLUDED
#define MATRIX_HPP_INCLUDED
#include <vector>
#include <algorithm>
class matrix
{
public:
typedef std::vector<double>::size_type st;
matrix() : rows_(0), cols_(0) {}
matrix(int r, int c) : rows_(r), cols_(c), coeffs_(st(r)*c,0.0) {}
void reset(int r, int c)
{ rows_=r; cols_=c; coeffs_.clear(); coeffs_.resize(st(r)*c,0.0); }
int rows() const {return rows_;}
int cols() const {return cols_;}
double const& operator()(int i, int j) const {return coeffs_[indexof(i,j)];}
double & operator()(int i, int j) {return coeffs_[indexof(i,j)];}
double const* operator[](int i) const {return &coeffs_[indexof(i,0)];}
double * operator[](int i) {return &coeffs_[indexof(i,0)];}
void swap(matrix& that)
{
std::swap(this->rows_,that.rows_);
std::swap(this->cols_,that.cols_);
this->coeffs_.swap(that.coeffs_));
}
private:
int rows_, cols_;
std::vector<double> coeffs_;
st indexof(int i, int j) const {return st(i)*cols+j;} // row major storage
};
inline void swap(matrix& a, matrix& b) {a.swap(b);}
matrix& operator+=(matrix& lhs, matrix const& rhs);
matrix operator+(matrix const& lhs, matrix const& rhs);
matrix operator*(matrix const& lhs, matrix const& rhs);
inline matrix& operator*=(matrix& lhs, matrix const& rhs)
{ matrix tmp = lhs * rhs; swap(tmp,lhs); return lhs; }
...
#endif
This way you won't waste any space for small matrices, and you can support large matrices. Also, the use of std::vector instead of a pointer member which points to dynamically allocated memory removes the need to define your own copy constructor, assignment operator and destructor.
这样你就不会为小矩阵浪费任何空间，而且你可以支持大矩阵。此外，使用 std::vector 而不是指向动态分配内存的指针成员消除了定义自己的复制构造函数、赋值运算符和析构函数的需要。
Of course, you could use boost::multi_array as a matrix replacement but using a custom matrix class allows you to declare overloaded operators in your own namespace which is desirable due to ADL (argument dependent lookup).
当然，您可以使用 boost::multi_array 作为矩阵替换，但使用自定义矩阵类允许您在自己的命名空间中声明重载运算符，由于 ADL（参数相关查找），这是可取的。
You might think that this doesn't really answer your question. In that case, let me stress that I think you don't fully understand how arrays and pointers work / behave. This is something you should look up in a decent C++ book. One could write many pages about this topic. You can't expect to see a short answer explaining all the quirks.
您可能认为这并不能真正回答您的问题。在这种情况下，让我强调一下，我认为您没有完全理解数组和指针的工作/行为方式。这是您应该在一本体面的 C++ 书中查找的内容。关于这个主题，人们可以写很多页。您不能期望看到解释所有怪癖的简短答案。
Check out the Definite C++ Book Guidethread.
回答by templatetypedef
The problem is that when passing multidimensional arrays as parameters in C++, you must specify the dimension of the outermost array. For example:
问题是在 C++ 中将多维数组作为参数传递时，必须指定最外层数组的维数。例如：
void ThisIsIllegal(int arr[][]); // Wrong!
void ThisIsAlsoIllegal(int arr[10][]); // Also wrong
void ThisIsLegal(int arr[][10]); // Okay
If you want to be able to have a function that takes in an array of any size, you can use templates:
如果您希望能够拥有一个接受任意大小数组的函数，您可以使用模板：
template <size_t N, size_t M>
void ThisIsAlsoLegal(int (&arr)[M][N]);
This last version accepts any multidimensional array of the right type, and is probably what you're looking for.
最后一个版本接受任何正确类型的多维数组，并且可能是您正在寻找的。
回答by Paul R
You need to specify all but the first dimension, e.g.
您需要指定除第一个维度之外的所有维度，例如
void Matrx::readMatrx(double a[][50])
From this you should be able to see that you have a fundamental problem with the way you have implemented your class, but at least you should now be able to get the code to compile.
从这里您应该能够看到您实现类的方式存在根本问题，但至少您现在应该能够编译代码。
回答by SVGreg
You can to specify all dimensions or only last dimension to pass an array:
您可以指定所有维度或仅最后一个维度来传递数组：
void Matrx::readMatrx(double a[][50])
{
for(int i=0;i< m;i++)
{
for(int j=0;j< n;j++)
A[i][j]=a[i][j];
}
}
回答by user543265
Thanks to all of you people...you were really helping...I have found myself a new definition of the class and the function definition for the matrix that fitted my need. I need you r comment on it...Below is the example of the class declaration..
感谢你们所有人……你们真的很有帮助……我找到了适合我需要的类的新定义和矩阵的函数定义。我需要你对此发表评论......下面是类声明的例子..
#include<iostream>
#include"stdafx.h"
using namespace std;
const int M=100; const int N=100;
class Matrix
{
double A[M][N];
int m,n;
public:
Matrix(void);
Matrix(int a, int b)
{
m=a;
n=b;
for(int i=0;i<m;i++)
{
for(int j=0;j<m;j++)
A[i][j]=0.0;
}
}
Matrix operator +(Matrix b);
Matrix operator -(Matrix b);
Matrix operator *(Matrix b);
void TransPose(Matrix b);
CString printMatrix();
void readMatrix(double*);
};
and then the function implementation
然后是函数实现
#include "stdafx.h"
#include "Matrix.h"
Matrix::Matrix(void)
{
}
Matrix Matrix::operator *(Matrix b)
{
Matrix c(m,m);
if(n!=b.m)
{
HWND hndOwner(0);
MessageBoxW(hndOwner,L"Multiplication not possible row and column does not match",L"Error",NULL);
Matrix errMat(1,0);
double er[1][1]={0}; errMat.readMatrix((double *)er);
return errMat;
}
for(int i=0;i< m;i++)
{
for(int k=0;k< m;k++)
{
c.A[i][k]=0;
for(int j=0;j< n;j++)
{
c.A[i][k] = c.A[i][k]+(A[i][j] * b.A[j][k]) ;
}
}
}
return c;
}
Matrix Matrix::operator +(Matrix b)
{
Matrix c(m,n);
if((n!=b.n)||(m!=b.m))
{
HWND hndOwner(0);
MessageBoxW(hndOwner,L"Addition not possible row and column does not match",L"Error",NULL);
Matrix errMat(1,0);
double er[1][1]={0}; errMat.readMatrix((double *)er);
return errMat;
}
for(int i=0;i<m;i++)
{
for(int j=0;j< n;j++)
{
c.A[i][j]=0.0;
}
}
for(int i=0;i< m;i++)
{
for(int j=0;j< n;j++)
{
c.A[i][j]=A[i][j]+b.A[i][j];
}
}
return c;
}
CString Matrix::printMatrix()
{
CString strB(" "),strDisp;
for(int iRow=0;iRow<m;iRow++)
{
for(int iColumn=0;iColumn<n;iColumn++)
{
strB.Format(L"%lf ",A[iRow][iColumn]);
strDisp+=strB;
}
strDisp+="\r\n";
}
return strDisp;
}
void Matrix::readMatrix(double *ptrarr)
{
for(int i=0;i< m;i++)
{
for(int j=0;j< n;j++)
A[i][j]=*(ptrarr+i*n+j);
}
}
void Matrix::TransPose(Matrix b)
{
for(int i=0;i<b.n;i++)
{
for(int j=0;j<b.m;j++)
A[i][j]=b.A[j][i];
}
}
The simple codes in the above are working well till now...if you have any suggestion for the improvement please suggest..
上面的简单代码到目前为止运行良好……如果您有任何改进建议，请提出建议……
回答by AucklandBoy
You're lucky, then because:
你很幸运，因为：
for(int j=0;j<m;j++)
A[i][j]=0.0;
should probably be:
应该是：
for(int j=0;j<**n**;j++)
A[i][j]=0.0;
