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      "depth": 2,
      "text": "构造函数不能声明为虚函数",
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      "text": "析构函数最好声明为虚函数",
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      "text": "函数不能返回局部变量的指针或引用的问题",
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      "text": "原因",
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      "text": "解决方法",
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      "text": "使用全局数组。使用全局变量时，在程序结束时才释放。",
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      "text": "使用new/malloc在堆上动态分配内存",
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      "text": "定义为静态类型",
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      "text": "用String类型",
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  "contentMarkdown": "# C++知识点与问题\n\n> 创建时间：2024/1/13 20:30\n\n## 构造函数不能声明为虚函数\n\n1）因为创建一个对象时需要确定对象的类型，而虚函数是在运行时确定其类型的。而在构造一个对象时，由于对象还未创建成功，编译器无法知道对象的实际类型，是类本身还是类的派生类等等\n2）虚函数的调用需要虚函数表指针，而该指针存放在对象的内存空间中；若构造函数声明为虚函数，那么由于对象还未创建，还没有内存空间，更没有虚函数表地址用来调用虚函数即构造函数了\n\n## 析构函数最好声明为虚函数\n\n首先析构函数可以为虚函数，当析构一个指向派生类的基类指针时，最好将基类的析构函数声明为虚函数，否则可以存在内存泄露的问题。\n如果析构函数不被声明成虚函数，则编译器实施静态绑定，在删除指向派生类的基类指针时，只会调用基类的析构函数而不调用派生类析构函数，这样就会造成派生类对象析构不完全。\n\n## 函数不能返回局部变量的指针或引用的问题\n\n## 原因\n\n不要返回函数体内局部变量的地址，因为函数结束时栈会回收，局部变量也随之销毁（如果局部变量为类对象，其析构函数会被自动调用），但可以返回局部变量本身。\n\n错误示例\n\n```cpp\nstring str1 = "test";\nstring str2 = "test";\n\n```\n\n## 解决方法\n\n### 使用全局数组。使用全局变量时，在程序结束时才释放。\n\n### 使用new/malloc在堆上动态分配内存\n\n> 不要忘记了，在使用完后要进行内存的释放，不然会造成内存的泄漏。分别用delete,free(),释放。使用delete时，会调用类的析构函数，而free则不会。\n\n```cpp\nstring str1 = "test";\nstring str2 = "test";\n\n```\n\n### 定义为静态类型\n\n```cpp\nstring str1 = "test";\nstring str2 = "test";\n\n```\n\n### 用String类型\n\n用string实现，是值拷贝!不存在释放内存会影响拷贝的问题。\n\n```cpp\nstring str1 = "test";\nstring str2 = "test";\n\n```\n\n### 使用字符串常量\n\n字符串常量存储在静态存储区域，所以一直都存在\n\n```cpp\nstring str1 = "test";\nstring str2 = "test";\n\n```\n\n### 在调用函数中定义指针\n\n```cpp\nstring str1 = "test";\nstring str2 = "test";\n\n```\n\n## Ref\n\nhttps://blog.csdn.net/xuyunyunaixuexi/article/details/81989201\n"
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