為什么此代碼片段存在分段錯誤？-有解無憂

這是我關于 Matrix 的代碼（我決定練習 OOP 撰寫自己的 Matrix 類）

矩陣.hpp

#ifndef MATRIX_HEADER
#define MATRIX_HEADER

typedef unsigned int u_int;

class Matrix
{
    double **mtrx;
    u_int x, y;

public:
    Matrix(u_int a, u_int b);
    Matrix(const Matrix &);
    ~Matrix();

    double det();

    Matrix operator (const Matrix &) const;
    Matrix operator-(const Matrix &) const;                           
    Matrix operator*(const Matrix &) const;
    friend Matrix operator*(const Matrix &, const double &);
    Matrix operator/(const Matrix &) const;
    double *operator[](const u_int idx) const { return mtrx[idx]; }

    bool IsEqual(const Matrix &) const;
    u_int GetX() const { return x; }
    u_int GetY() const { return y; }
};

#endif

矩陣.cpp

#include "Matrix.hpp"

Matrix::Matrix(u_int a, u_int b) : x(a), y(b)
{
    mtrx = new double *[x];
    for (u_int i = 0; i < x; i  )
        mtrx[i] = new double[y];
}

Matrix::Matrix(const Matrix &ref)
{
    if (mtrx)
    {
        for (u_int i = 0; i < x; i  )
            delete[] mtrx[i];
        delete[] mtrx;
    }
    x = ref.x;
    y = ref.y;
    *mtrx = new double[x];
    for (u_int i = 0; i < x; i  )
        mtrx[i] = new double[y];
}

Matrix::~Matrix()
{
    if (mtrx)
    {
        for (u_int i = 0; i < x; i  )
            delete[] mtrx[i];
        delete[] mtrx;
    }
}

bool Matrix::IsEqual(const Matrix &a) const     // If sizes of matrixes are equal
{                                               // matrixes are equal
    return (a.GetX() == x) && (a.GetY() == y);
}

Matrix Matrix::operator (const Matrix &a) const
{
    if (!IsEqual(a))                            // Check on equality matrixes
        return Matrix(1,1);                     // I have not any idea yet what          
    Matrix matrix(x, y);                        // should it give is sizes 
    for (u_int i = 0; i < x; i  )               // of Matrix are not equal
        for (u_int j = 0; j < y; j  )
            matrix[i][j] = a.mtrx[i][j]   mtrx[i][j];
    return matrix;
}

主檔案

#include <stdio.h>
#include "Matrix.hpp"

int main()
{
    Matrix a(2, 5);
    Matrix b(2, 5);
    for (u_int i = 0; i < a.GetX(); i  )
    {
        for (u_int j = 0; j < a.GetY(); j  )
        {
            a[i][j] = i   j;
        }
    }
    for (u_int i = 0; i < b.GetX(); i  )
    {
        for (u_int j = 0; j < b.GetY(); j  )
        {
            b[i][j] = i   j;
        }
    }
    Matrix c = a   b;
    return 0;
}

當我打開我的程式時，添加兩個矩陣后它會引發分段錯誤。在這種情況下，對我來說更有趣的是Matrix.cpp, Matrix Matrix::operation ....

當我洗掉這 2 行（檢查相等 2 矩陣）時，當我打開我的程式時，它不會給我一個分段錯誤，但是當我添加這 2 行時，程式給我一個 sf 你能告訴我為什么它是這樣作業的嗎？

uj5u.com熱心網友回復：

您可能會考慮使用一維陣列而不是double[x*y]二維陣列。它將使記憶體管理更容易一些，因為您將只有 1 個陣列要處理，而不是多個陣列。double*[x]double[y]

在任何情況下，您的Matrix(const Matrix &)復制建構式都不應該包含delete[]任何內容mtrx，因為mtrx尚未初始化（它指向隨機記憶體）。并且該建構式的其余部分也沒有正確分配陣列。您在建構式中正確分配了陣列Matrix(u_int, u_int)，因此只需將該邏輯復制到復制建構式中。double然后通過實際復制正在復制的值來完成復制建構式Matrix。

至于operator ，如果您不知道應該return為不同大小的矩陣做什么，那么我建議您throw改為例外。

此外，即使您當前的代碼還沒有使用它，您也應該添加一個復制分配operator=來完成規則 3（您已經有一個復制建構式和一個解構式）。

試試這個：

#ifndef MATRIX_HEADER
#define MATRIX_HEADER

typedef unsigned int u_int;

class Matrix
{
    double **mtrx;
    //or: double *mtrx;
    u_int x, y;

public:
    Matrix(u_int a, u_int b);
    Matrix(const Matrix &);
    ~Matrix();

    double det();

    Matrix& operator=(const Matrix &);

    Matrix operator (const Matrix &) const;
    Matrix operator-(const Matrix &) const;                           
    Matrix operator*(const Matrix &) const;
    friend Matrix operator*(const Matrix &, const double &);
    Matrix operator/(const Matrix &) const;

    double* operator[](const u_int idx) const {
        return mtrx[idx];
        //or: return &mtrx[idx*x];
    }

    bool IsEqualSize(const Matrix &) const;
    u_int GetX() const { return x; }
    u_int GetY() const { return y; }
};

#endif

#include "Matrix.hpp"
#include <utility>
#include <stdexcept>

Matrix::Matrix(u_int a, u_int b)
    : x(a), y(b)
{
    mtrx = new double*[x];
    for (u_int i = 0; i < x;   i) {
        mtrx[i] = new double[y];
    }

    // or: mtrx = new double[x*y];
}

Matrix::Matrix(const Matrix &ref)
    : x(ref.x), y(ref.y)
{
    mtrx = new double*[x];
    for (u_int i = 0; i < x;   i) {
        mtrx[i] = new double[y];
        for (u_int j = 0; j < y;   j) {
            mtrx[i][j] = ref.mtrx[i][j];
        }
    }

    /* or:
    u_int size = x*y;
    mtrx = new double[size];
    for (u_int i = 0; i < size;   i) {
        mtrx[i] = ref.mtrx[i];
    }
    */
}

Matrix::~Matrix()
{
    // this loop is not needed for a 1D array...
    for (u_int i = 0; i < x;   i) {
        delete[] mtrx[i];
    }

    delete[] mtrx;
}

bool Matrix::IsEqualSize(const Matrix &a) const
{
    return (a.GetX() == x) && (a.GetY() == y);
}

Matrix& Matrix::operator=(const Matrix &a)
{
    if (&a != this)
    {
        Matrix tmp(a);
        std::swap(mtrx, tmp.mtrx);
    }
    return *this;
}

Matrix Matrix::operator (const Matrix &a) const
{
    if (!IsEqualSize(a))
        throw std::logic_error("Cannot add matrices of different sizes");

    Matrix matrix(x, y);

    for (u_int i = 0; i < x;   i) {
        for (u_int j = 0; j < y;   j)
            matrix.mtrx[i][j] = mtrx[i][j]   a.mtrx[i][j];
    }

    /* or:
    u_int size = x*y;
    for (u_int i = 0; i < size;   i) {
        matrix.mtrx[i] = mtrx[i]   a.mtrx[i];
    }
    */

    return matrix;
}

...

#include <stdio.h>
#include "Matrix.hpp"

int main()
{
    Matrix a(2, 5);
    Matrix b(2, 5);

    for (u_int i = 0; i < a.GetX();   i)
    {
        for (u_int j = 0; j < a.GetY();   j)
        {
            a[i][j] = i   j;
        }
    }

    for (u_int i = 0; i < b.GetX();   i)
    {
        for (u_int j = 0; j < b.GetY();   j)
        {
            b[i][j] = i   j;
        }
    }

    Matrix c = a   b;

    return 0;
}

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