c++ - 赋值运算符重载——删除堆内存导致崩溃

Question

我正在写一个字符串类，在进行赋值运算符重载时，我观察到在我们删除以前分配的内存的部分发生崩溃。我试图通过代码进行追踪，但无法弄清楚。任何指针都会有所帮助

str& str::operator=(const str &Rhs)
{
    if (this != &Rhs)
    {
        cout << " attempt of self allocation - " << endl;
        **delete[] this->_element;**   // crashes here

        this->_capacity = Rhs._capacity;
        this->_display = Rhs._display;
        this->_size = Rhs._size;


        if (Rhs._size > 0)
        {
            this->_element = new char(this->_size);
            if (this->_element == NULL)
            {
                cout << " mem allocation failed " << endl;
            }
        }

        for (int counter = 0; counter <= this->_size; counter++)
        {
            this->_element[counter] = Rhs._element[counter];
        }
    }

    return *this;
}
/*copy constructor */
str::str(const str& Rhs)
{
    // copy constructor called 
    this->_capacity = Rhs._capacity;
    this->_display = Rhs._display;
    this->_size = Rhs._size;

    if (Rhs._size > 0)
    {
        this->_element = new char(_size);
        if (this->_element == NULL)
        {
            cout << " mem allocation failed " << endl;
        }

        for (int counter = 0; counter <= this->_size; counter++)
        {
            this->_element[counter] = Rhs._element[counter];
        }
    }
}

/*构造函数*/

str::str(const char *Y)
{
    cout << "constructor called !!! -- " <<  endl;
    size_t len = this->stringlen(Y);
    this->_element = new char(len + 1);
    for (int counter = 0; counter < len; counter++)
    {
        this->_element[counter] = Y[counter];
    }
    this->_element[len] = '\0';

    this->_size = len + 1;

    cout << "string in constructor is -- " << this->_element << endl;
}

来自.h文件

class str 
{
public:
    /*Default Constructor*/
    explicit str();

    /*Constructor with single char Argument*/
    explicit str(char x);

    /*Constructor with char array Argument*/
    explicit str(const char* Y);

    /* Creating new element with copy constructor */
    str(const str& Rhs);

    /* Overloading of Assignment operator */ 
    str& operator=(const str& Rhs);

    friend int string_compare(const str& Lhs, const str& Rhs);
    int reverse();
    size_t stringlen(const char* Y);
    str& operator+(str& Rhs);
    bool operator==(const str& Rhs);
    bool operator!=(const str& Rhs);
    friend ostream& operator<<(ostream &out, str& Lhs);


private:
char*  _element;
int _capacity;
bool _display;
int _size; //largest accessed + 1
};

主例程 -

void test1() {
  const char *j = "abc";
  cout << "length of j = " << strlen(j) << endl;
  str s1('U');
  str s2("hello");
  cout << s2 << endl;
  s2.reverse();
  cout << s2 << endl;
  str s3(s2);
  cout << s1 << endl;
  cout << s2 << endl;
  cout << s3 << endl;
  **s2 = s1;**  // crashes
  cout << s2 << endl;
  cout << s1 << endl;

Answer 1

您的代码有几个问题。

• 最大的一个是:如果你想分配一个数组你需要使用new char[_size]。 new char(_size) 分配一个 char，其值设置为 _size。

• 其次，一旦您解决了该问题，您就会写入已分配数组的末尾 - 根据 header 中的注释判断，您需要分配 char[_size + 1]。

• 第三，在您的复制构造函数中，您永远不会初始化 _element 数组，并且在您的赋值运算符中，您永远不会清除 _element 值。当您复制或分配一个空的 str 然后尝试分配给它时(或者在销毁时，我假设析构函数也调用 delete )，这最终会导致崩溃.