c++ - 无效的对象访问 C++

Question

我试图运行 Stroustroup 的 C++ 书中的这段代码，我添加了一些代码，因为书中没有所有内容。我一直遇到以下问题。我知道这里有多个关于同一个错误的问题，但我的代码不同，因此出现了这个问题。

错误是

copy(5826,0x7fff76b09300) malloc: * error for object 0x7ff6a9404c18: incorrect checksum for freed object - object was probably modified after being freed. * set a breakpoint in malloc_error_break to debug Abort trap: 6

#include<stdio.h>
#include<iostream>

using namespace std;
class Vector {
private:
    double * elem; // elem points to an array of sz doubles
    int sz;
public:
    Vector(int s) {
        sz = s;
        elem = new double[sz];
        for (int i = 0; i<sz; i++) {
            elem[i] = i;
        }
    }
    ~Vector() { delete[] elem; } // destructor: release resources
    Vector(const Vector& a); // copy constructor
    Vector& operator=(const Vector& a); // copy assignment
    double& operator[](int i);
    const double& operator[](int i) const;
    int size() const;
};


Vector::Vector(const Vector& a) // copy constr uctor
{
    elem = new double[sz], // allocate space for elements
        sz = a.sz;
    for (int i = 0; i != sz; ++i) // copy elements
        elem[i] = a.elem[i];
}


double& Vector::operator[](int k) {
    return this->elem[k];
}


Vector& Vector::operator=(const Vector& a) // copy assignment
{
    double* p = new double[a.sz];
    for (int i = 0; i != a.sz; ++i)
        p[i] = a.elem[i];
    delete[] elem; // delete old elements
    elem = p;
    sz = a.sz;
    return *this;
}


int main() {
    Vector v1(10);
    Vector v2 = v1;
    v1[0] = 2;
    v2[1] = 3;
    cout << v1[0] << "\n";
    return 0;
}

Answer 1

你的复制构造函数应该反转两行，因为你还没有为 sz 设置值。

Vector::Vector(const Vector& a) // copy constructor
{
    elem = new double[sz];
    sz = a.sz;
    for (int i=0; i!=sz; ++i)
        elem[i] = a.elem[i];
}

所以你可以这样做

Vector::Vector(const Vector& a) // copy constructor
{
    sz = a.sz;
    elem = new double[sz];
    for (int i=0; i!=sz; ++i)
        elem[i] = a.elem[i];
}