如何为我的非静态转置函数实现 matrix.Transpose()？

Question

我在 test.cpp 文件中得到了以下代码来实现：

cout << "Case 2: the non-static Transpose function" << endl;
{
    double column[4] = {2, 1, 0, -1};
    double row[3] = {2, 0, -1};
    Matrix matrix = Matrix::Toeplitz(column, 4, row, 3);
    cout << "The original Matrix = " << endl;
    cout << matrix << endl;  //This part of the code works


    matrix.Transpose();  //How do I implement this?
    cout << "The transposed version = " << endl;
    cout << matrix << endl;
    cout << "Press any key to continue ..." << flush;
    system("read");
    cout << endl;
}

Matrix::Toeplitz(column, 4, row, 3) 的工作方式如下：

Matrix Matrix::Toeplitz(const double* column, const int noOfRows, const double* row, const int noOfColumns){
    Matrix outT(column, noOfRows, row, noOfColumns);
    return outT;
}

那么我将如何实施 matrix.Transpose()？到目前为止我的代码如下：

Matrix& Matrix::Transpose () {

double newrow[noOfRows];
for(int i=0; i<noOfRows; i++){
    int index = GetIndex(i,0);
    newrow[i] = data[index];
}

double newcol[noOfColumns];
for(int i=0; i<noOfColumns; i++){
    int index = GetIndex(0,i);
    newcol[i] = data[index];
}

Matrix outT(newcol, noOfColumns, newrow, noOfRows);
}

这对cout<<matrix<<endl;

没有影响

我在想 Matrix outT(newcol, noOfColumns, newrow, noOfRows); 应该在实现 matrix.Transpose 时向矩阵对象提供新信息（即切换列和行数组），但它一直没有工作。

这是实现 matrix.Transpose() 的正确格式 Matrix& Matrix::Transpose () 吗？

Answer 1

Matrix::Transpose 不能 return 引用本地声明的对象。这会导致很多问题。

见C++ Returning reference to local variable。

必须return复制（然后，函数可以是const，因为当前对象没有被修改）：

Matrix Matrix::Transpose() const
{
    double newrow[noOfRows];
    for(int i=0; i<noOfRows; i++){
        int index = GetIndex(i,0);
        newrow[i] = data[index];
    }

    double newcol[noOfColumns];
    for(int i=0; i<noOfColumns; i++){
        int index = GetIndex(0,i);
        newcol[i] = data[index];
    }

    return Matrix(newcol, noOfColumns, newrow, noOfRows);
}

那么，你这样使用：

Matrix transposed = matrix.Transpose(); // does not modify matrix object
cout << "The transposed version = " << endl;
cout << transposed << endl;

如果returning Matrix&，你需要让你的方法转置当前对象和return它（return *this），只对帮助调用者链接有用许多运算符（例如 m.Transpose().Transpose()）。

那么，可以（未测试）：

Matrix& Matrix::Transpose() 
{
    // backup old content
    double* backupData = new double[noOfRows*noOfColumns];
    memcpy( backupData, data, sizeof(double)*noOfRows*noOfColumns );

    // change matrix geometry
    int oldRowCount = noOfRows;
    noOfRows = noOfColumns;
    noOfColumns = oldRowCount ;

    // transpose matrix by copying from backup content
    for ( unsigned int line = 0; line < noOfRows ; ++line )
    {
        for ( unsigned int col = line; col < noOfColumns; ++col )
        {
            data[line * noOfColumns + col] = backupData[col * noOfRows  + line];
        }
    }

    delete [] backupData;

    return *this;
}

那么，你这样使用：

matrix.Transpose(); // modifies matrix object
cout << "The transposed version = " << endl;
cout << transposed << endl;

如何为我的非静态转置函数实现 matrix.Transpose()？

How do I implement matrix.Transpose() for my non-static Transpose function?

c++

transpose

matrix

non-static