C++返回类型限定符天堂

Question

实际上真是太棒了.有人可以用简单的英语解释为什么下面的部分工作与否？

class Hey;

class Bitmap {

public:
    const Hey* const& getHey() { return hey; }; // works
    const Hey* & getHey2() { return hey; }; // error C2440: 'return' : cannot convert from 'Hey *' to 'const Hey *&'

private:
    Hey* hey;
};

Answer 1

您不能添加const多个深度本身不是指针的指针const,因为这样您就可以将const变量的地址填充到非const指针中.考虑:

char c;
char* p = &c;
const char* cp = p; // ok, only one type deep
const char x;
cp = &x; // ok
const char*& r = p; // fail, because...
r = cp; // ok
*p = 5; // ok, would overwrite a const variable if binding r to p were allowed

制作指针const以不同的方式防止这种灾难.继续这个例子:

const char* const& cr = p; // ok
cr = cp; // fail, cr is const, saving us from...
*p = 5; // would overwrite a const variable if cr = cp were allowed