How to prevent pointers from dangling in C++?

How to prevent pointer dangling? Pointer dangling is a situation where a pointer points to a memory area that has been freed or destroyed. Preventing dangling pointers is critical to ensure the robustness and reliability of your code. Pointer dangling can be prevented by using smart pointers, containers, and weak_ptr to automatically manage the pointer's lifetime and avoid dangling pointers.

How to prevent pointer dangling in C++

A dangling pointer refers to a situation where a pointer points to a memory area that has been freed or destroyed. It can cause undefined behavior, including crashes or data corruption. Preventing dangling pointers is critical to ensure the robustness and reliability of your code.

Identifying dangling pointers

Common causes of dangling pointers include:

• Incorrect handling of pointers to heap-allocated memory
• Forgetting to update a pointer stored in Pointers in data structures
• Delete the reference to the referenced object before it is destroyed

Methods to prevent pointer dangling

There are several ways to prevent pointer dangling Type:

1. Use smart pointers:

Smart pointers are libraries provided by C++ that can automatically manage the life cycle of pointers pointing to heap-allocated memory. Smart pointers ensure that memory is automatically released when it is no longer needed, eliminating the risk of dangling pointers.

// 使用 unique_ptr 拥有一个指针
std::unique_ptr<int> ptr = std::make_unique<int>(10);

// ptr 的生命周期与该块结束时结束
{
    // 在此块内使用 ptr
}

// 超出块的范围后，ptr 将自动释放指向的内存

2. Use containers:

Containers automatically manage the memory of their elements and release elements when they are no longer needed. This eliminates the need to manually manage memory for pointers stored in the container, thereby reducing the risk of dangling pointers.

// 使用 vector 存储指针
std::vector<int*> ptrs;

// 添加指针
ptrs.push_back(new int(10));
ptrs.push_back(new int(20));

// vector 将在销毁时自动释放分配的内存

3. Use weak_ptr:

weak_ptr is a smart pointer that points to an object that may have been destroyed. It does not prevent deletion of the object and becomes invalid after the object is destroyed. This prevents dangling pointers from being used when the object no longer exists.

// 创建一个普通指针
std::shared_ptr<int> shared_ptr = std::make_shared<int>(10);

// 创建一个弱指针，指向共享指针指向的对象
std::weak_ptr<int> weak_ptr = shared_ptr;

// 销毁共享指针
shared_ptr.reset();

// 检查 weak_ptr 是否有效
if (weak_ptr.expired()) {
    // weak_ptr 指向的对象已被销毁
}

Practical case

Consider the situation where the pointer is dangling in the following example:

int* ptr = new int(10);
delete ptr;
ptr = new int(20); // 指针悬垂

// 使用 ptr 时会导致未定义的行为

In order to prevent the pointer from dangling in this situation, you can use smart pointers to manage the life cycle of the pointer. :

std::unique_ptr<int> ptr = std::make_unique<int>(10);
ptr.reset(new int(20)); // 正确地更新指向新分配的内存的指针

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