英文:
C++ Compilation problem with creating an array of struct from the heap
问题
以下是翻译好的部分：
- 构造函数：
MyClass(int xx, int yy) : x(xx), y(yy){m_BufferPtr = new struct BufferCustom[CONST_BUFFER_SIZE];}
编译错误：分配不完整类型 struct BufferCustom 的内存。
- 析构函数中的警告：
if (m_BufferPtr){delete [] m_BufferPtr;m_BufferPtr = nullptr;}
警告：删除不完整类型 'struct BufferCustom' 的指针可能导致未定义行为。
我对为什么会出现这个错误感到困惑！
英文:
I'm getting a compilation error and warning when I compile this.
#include <iostream>struct {uint8_t m_data;int size;} BufferCustom;class MyClass{private:int x, y;const int CONST_BUFFER_SIZE = 10;struct BufferCustom *m_BufferPtr;public:MyClass(int xx, int yy) : x(xx), y(yy){m_BufferPtr = new struct BufferCustom[CONST_BUFFER_SIZE];}virtual ~MyClass() {if (m_BufferPtr){delete [] m_BufferPtr;m_BufferPtr = nullptr;}}// user defined copy constructorMyClass(const MyClass& rhs): x{ rhs.x }, y{ rhs.y } // initialize members with other object's // members{std::cout << "User defined copy constructor invoked.";//m_BufferPtr = new struct B}MyClass& operator=(const MyClass &rhs){std::cout << "Assignment operator called\n";return *this;}};int main(){MyClass o1{ 1, 2 };MyClass o2 = o1; // user defined copy constructor invokedo2 = o1;}
The error(s) are in these lines:
- Ctor
MyClass(int xx, int yy) : x(xx), y(yy){m_BufferPtr = new struct BufferCustom[CONST_BUFFER_SIZE];}
compilation error being Allocation of incomplete type struct BufferCustom
- The second warning is in the dtor
if (m_BufferPtr){delete [] m_BufferPtr;m_BufferPtr = nullptr;}
saying that Deleting pointer to incomplete type 'struct BufferCustom' may cause undefined behavior
I am perplexed as to why this is an error!
答案1
得分: 6
这段代码：
struct {uint8_t m_data;int size;} BufferCustom;
...定义了一个具有匿名类型的结构体，然后定义了一个名为BufferCustom的该类型的实例。所以BufferCustom是一个没有名称的类型的单个变量。
但是您后来的代码尝试将BufferCustom用作类型的名称。我猜您的本意可能是这样：
struct BufferCustom {uint8_t m_data;int size;};
这将BufferCustom定义为类型的名称，因此您可以随后分配类型为BufferCustom的对象。
英文:
This:
struct {uint8_t m_data;int size;} BufferCustom;
...defines a struct with an anonymous type, then defines one instance of that type named BufferCustom. So BufferCustom is a single variable of a type that doesn't have a name.
But your later code attempts to use BufferCustom as if it were the name of a type. I'd guess what you intended was something like this instead:
struct BufferCustom {uint8_t m_data;int size;};
This defines BufferCustom as the name of the type, so you can later allocate objects of type BufferCustom.
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