C 中的析構(gòu)函數(shù)是一種特殊的成員函數(shù)，會(huì)在對(duì)象離開作用域或被顯式刪除時(shí)自動(dòng)調(diào)用。它的主要作用是清理對(duì)像在其生命週期內(nèi)可能獲取的資源，如內(nèi)存、文件句柄或網(wǎng)絡(luò)連接。析構(gòu)函數(shù)在以下情況下自動(dòng)調(diào)用：局部變量離開作用域時(shí)、對(duì)指針調(diào)用delete時(shí)、包含對(duì)象的外部對(duì)象析構(gòu)時(shí)。定義析構(gòu)函數(shù)時(shí)需在類名前加~，且無(wú)參數(shù)和返回值。若未定義，編譯器會(huì)生成默認(rèn)析構(gòu)函數(shù)，但不會(huì)處理動(dòng)態(tài)內(nèi)存釋放。注意事項(xiàng)包括：每個(gè)類只能有一個(gè)析構(gòu)函數(shù)，不支持重載；建議將繼承類的析構(gòu)函數(shù)設(shè)為virtual；派生類析構(gòu)函數(shù)先執(zhí)行，再自動(dòng)調(diào)用基類析構(gòu)函數(shù)。使用基類指針刪除派生類對(duì)象時(shí)，基類析構(gòu)函數(shù)必須為virtual，否則行為未定義。儘管現(xiàn)代C 推薦使用智能指針和RAII模式，理解析構(gòu)函數(shù)的工作機(jī)制仍然重要，尤其在處理遺留代碼或性能敏感系統(tǒng)時(shí)。

A destructor in C is a special member function that gets called automatically when an object goes out of scope or is explicitly deleted. Its main job is to clean up resources that the object might have acquired during its lifetime — like memory, file handles, or network connections.

When Is a Destructor Called?

Destructors run automatically under certain conditions:

• When a local (automatic) variable goes out of scope
• When delete is called on a pointer to an object
• When an object is part of another object (like a member variable), and the outer object's destructor runs

You don't need to call it manually unless you're managing raw pointers and using dynamic memory allocation.

Examples include:

• A class that opens a file in its constructor should close it in the destructor.
• An object that allocates memory with new should free it with delete .

How to Define a Destructor

You define a destructor by putting a tilde ~ before the class name, and it takes no arguments and returns nothing:

 class MyClass {
public:
    ~MyClass() {
        // Cleanup code here
    }
};

If you don't define one, the compiler will generate a default destructor for you — but it won't handle custom cleanup like freeing dynamically allocated memory.

Some things to keep in mind:

• You can only have one destructor per class — no overloading
• It's good practice to make destructors virtual if your class is meant to be inherited from

Destructors and Inheritance

When dealing with derived classes:

• The destructor of the derived class runs first
• Then the base class destructor is called automatically

This ensures that anything set up by the base class is safely cleaned up after the derived class is done.

If you're deleting a derived class object through a base class pointer, always declare the base class destructor as virtual . Otherwise, the behavior is undefined.

So instead of this:

 class Base {};

Do this:

 class Base {
public:
    virtual ~Base() {}
};

This small detail helps prevent resource leaks in polymorphic types.

Final Notes

Destructors are crucial for proper resource management in C . While modern C encourages the use of smart pointers and RAII (Resource Acquisition Is Initialization), understanding how destructors work is still essential, especially when working with legacy code or performance-critical systems.

They aren't complicated, but they do require careful handling — especially when manual memory management is involved.

基本上就這些。

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