C++ destructor called before lifetime of scope

Question

I have a question about triggering a destructor for an object prematurely. I have an dynamically allocated array of pointers to dynamically allocated Word objects. The name of the array is words_. words_ is a class attribute of another class called Dictionary.

In my Dictionary class, I have a function where I access each Word object and call a member function of the Word class.

The below code triggers the destructor prematurely:

Word *curr_word_ptr = words_[idx]; // This line is okay, doesn't trigger destructor
Word curr_word = *curr_word_ptr; // This line triggers the destructor prematurely
curr_word.callMemberFunc();

Because of the second line, as soon as the scope of the function ends, the destructor is called.

But if I access it through the array indices alone:

*(words_[idx]).callMemberFunc(); // The desctructor is not called prematurely

Is the problem because I have a stack variable (not even a stack pointer variable) accessing a dynamically allocated object? Thus, when the scope of the function ends, both the stack variable (curr_word) and the dynamically allocated stack object gets destroyed?

Thank you.

Answer 1

Word curr_word = *curr_word_ptr; defines a local Word, that only lives in the local scope, your function. When the function exits, it is destroyed. Note it is a copy of the initial Word that is destroyed, not the original.

如果您想要方便的语法以便不必全部取消引用或复制，请使用引用：

Word &word = *curr_word_ptr;

这是 C++ 提供的语法糖，用于引用没有指针的对象（直接）。但请注意，word在这种情况下，对 所做的任何更改也会影响您的原始单词。

如果您的Words 包含动态分配的内存，则问题会更糟。假设您使用默认的复制构造函数，地址将被复制。因此，销毁本地Word将释放仍由原始 引用的内存Word，从而在下次访问时导致崩溃。