Question

我是c ++编程的新手（实际上是一般的编程），而且我在c ++程序中遇到了一些复制构造函数的问题，该程序应该证明矩阵的添加。

我认为我的程序没有到达复制构造函数，但我不知道为什么。我理解为什么如果我没有定义复制构造函数，我应该期望这不起作用，因为析构函数会删除matrix result指向的数据。但是，我已经定义了一个拷贝构造函数。我哪里出错？

非常感谢帮助！

我的代码如下：

#include<iostream>
#include<string>
#include<stdlib.h> // for c style exit
using namespace std;

class matrix
{
private:
    double* mdata;
    int rows, columns;
public:
    // Declare the << operator as a friend of the class. 
    friend ostream& operator<<(ostream&, const matrix&);
    // Define the default constructor.
    matrix() : mdata(0), rows(0), columns(0) {}
    // Define the parameterized constructor.
    matrix(int numberOfRows, int numberOfColumns) : mdata(new double[numberOfColumns*numberOfColumns]), rows(numberOfRows), columns(numberOfColumns) {
        for (int i{ 0 }; i <= numberOfColumns*numberOfRows; i++){
            mdata[i] = 0;
        }
    }
    // Define the copy constructor.
    matrix(const matrix& matr) {
        cout << endl << "Reached copy constructor." << endl;
        rows = matr.getrows();
        columns = matr.getcols();
        mdata = 0;
        if (matr.mdata){
            mdata = new double[(matr.getrows())*(matr.getcols())];
            for (int i{ 0 }; i <= rows*columns ; i++){
                mdata[i] = matr.mdata[i];
                cout << mdata[i] << endl;
            }
        }
        else {
            mdata = 0;
        }
    }

    // Define the destructor.
    ~matrix() { 
        cout << "Destructor called on " << endl << *this;
        delete[] mdata; 
    }

    // Return the number of rows.
    int getrows() const { return rows; }
    // Return the number of columns.
    int getcols() const { return columns; }
    // Return the position in the array of element (m,n).
    int index(int m, int n) const {
        if (m>0 && m <= rows && n>0 && n <= columns) return (n - 1) + (m - 1)*columns;
        else {
            cout << "Error: out of range. Press any key to exit." << endl;
            // For holding the program before exit. 
            exit(1);
        }
    }
    // Allows array elements to be accessed with bracket notation. 
    double& operator()(int m, int n) const { return mdata[index(m, n)]; }
    matrix& operator+(const matrix&) const;

    // A function for edditing matrix elements
    void setValue(int m, int n, double value) {
        mdata[index(m, n)] = value;
    }
};

// Define the << operator for printing matrices. This is a friend of the class. 
ostream& operator<<(ostream &os, const matrix &mat){
    // Deals with case of matrix with zero size. 
    if (mat.rows == 0 && mat.columns == 0){
        cout << "This matrix is has no size." << endl;
    }
    // If the matrix has non-zero size,
    else {
        // For each row in the matrix,
        for (int i{ 1 }; i <= mat.rows; i++) {
            cout << "[";
            // For each column in that row
            for (int j{ 1 }; j <= mat.columns; j++){
                // Print the element, followed by a comma.
                if (j < mat.columns){
                    cout << mat(i, j) << ", ";
                }
                // Ensures no comma is placed after last elemet in row. 
                else{
                    cout << mat(i, j);
                }
            }
            os << "]" << endl;
        }
    }
    return os;
}
// The addition operator
matrix& matrix::operator+(const matrix& mat) const {
    matrix result(rows, columns);
    // If the matrix dimensions are different,
    if (rows != mat.getrows() || columns != mat.getcols()){
        cout << "Cannot add two matrices with differing dimensions." << endl;
        string exitStr;
        cout << "Enter any key to exit." << endl;
        cin >> exitStr;
        // Exit the program
        exit(1);
    }
    // Otherwise, create a matrix with the appropriate dimensions
    else{
        // For each element in result
        for (int k{ 1 }; k <= result.getrows(); ++k){
            for (int l{ 1 }; l <= result.getcols(); ++l){
                // That element is the sum of the corresponding elements in the two input matrices. 
                result.setValue(l,k,(mat(l, k) + (*this)(l, k)));
            }
        }
    }
    return result;
}


// Main program

int main()
{
    // Demonstrate default constructor
    matrix a1;
    cout << "Matrix a1: ";
    cout << a1;

    // Demonstrate parameterized constructor
    const int m(2), n(2);
    matrix a2(m, n);
    // Set values for a2
    a2.setValue(1, 1, 1);
    a2.setValue(2, 2, 1);
    a2.setValue(1, 2, 1);
    a2.setValue(2, 1, 1);
    // Print matrix a2
    cout << "a2 = " << endl << a2 << endl;

    // Demonstrate parameterized constructor
    matrix a3(m, n);
    // Set values for a3
    a3.setValue(1, 1, 2);
    a3.setValue(2, 2, 2);
    a3.setValue(1, 2, 2);
    a3.setValue(2, 1, 2);
    // Print matrix a3
    cout << "a3 = " << endl << a3 << endl;

    // Create matrix a4
    matrix a4(a2 + a3);
    cout << endl << "The sum of a2 and a3 is: " << endl << a4;

    // For halting the program. 
    int x;
    cin >> x;
    return 0;
}

Answer 1

for（int i {0}; i＆lt; = numberOfColumns * numberOfRows; i ++）

应该是

for（int i {0}; i＆lt; numberOfColumns * numberOfRows; i ++）

你正在循环N + 1而不是N

c ++拷贝构造函数生成运行时错误

1 个答案: