QT代码，重载函数d_func()声明形式分析和调用关系分析

QT代码，重载函数d_func()声明形式分析和调用关系分析

#define X_DECLARE_PRIVATE(Class) \
    inline Class##Private* d_func() { return reinterpret_cast<Class##Private *>(xGetPtrHelper(d_ptr)); } \
    inline const Class##Private* d_func() const { return reinterpret_cast<const Class##Private *>(xGetPtrHelper(d_ptr)); } \
    friend class Class##Private;

#include <stdio.h>

class A
{
public:
	A(int a)
	{
		giCnt = a;
	}

	inline int* d_func()
	{
		printf("111\n");
		return reinterpret_cast<int *>(&giCnt);
	}
       
    
	inline const int* d_func()
	{
		printf("222\n");
		return reinterpret_cast<const int *>(&giCnt);
	}
public:
	int giCnt;

};

int main()
{
	A a(4);
	int* d = a.d_func();
	return 0;
}

1、编译失败，函数返回值有区别，不构成重载，编译器认为是通一个函数，函数重定义，编译失败

#include <stdio.h>

class A
{
public:
	A(int a)
	{
		giCnt = a;
	}

	inline int* d_func()
	{
		printf("111\n");
		return reinterpret_cast<int *>(&giCnt);
	}
       
    
	inline int* d_func() const
	{
		printf("222\n");
		return reinterpret_cast<int *>(&giCnt);
	}
public:
	int giCnt;

};

int main()
{
	A a(4);
	int* d = a.d_func();
	return 0;
}

2、编译失败，失败信息如下：

error: reinterpret_cast from type ‘const int*’ to type ‘int*’ casts away qualifiers
   return reinterpret_cast< int *>(&giCnt);

当成员函数加上const后，该函数会将所有的成员变量前增加const属性处理，因此&giCnt为const int*的类型

#include <stdio.h>

class A
{
public:
	A(int a)
	{
		giCnt = a;
	}

	inline int* d_func()
	{
		printf("111\n");
		return reinterpret_cast<int *>(&giCnt);
	}

	inline const int* d_func() const
	{
		printf("222\n");
		return reinterpret_cast<const int *>(&giCnt);
	}
public:
	int giCnt;

};

int main()
{
	A a(4);
	a.d_func();
	const A b(3);
	b.d_func();
	return 0;
}

3、编译成功，输出结果：

111
222