如何重载

Question

template<long long X>
class Bitset
{
    public: std::vector<unsigned char> bit = std::vector<unsigned char> ((X+7)/8);

    public:
        /* constructors */

        friend std::ostream &operator<< (std::ostream &output, const char x);
};

std::ostream &operator<< (std::ostream &output, const char x)
{
    output<<(short)(x);
    return output;
}

Bitset a;
/* code */
cout << a.bit[x];
cout << 'a';

Answer 1

不能重载运算符<<，以便char按您希望的方式运行。它不知道char来自哪里，因此它不能根据源代码有不同的行为。

为了按照您所希望的方式工作，您必须使bitset实现它自己的运算符[]，该运算符返回代理对象，然后您可以为该代理重载运算符<<，例如：

template<long long X>
class Bitset
{
private:
    std::vector<unsigned char> bits = std::vector<unsigned char> ((X+7)/8);

public:
    /* constructors */

    class BitProxy
    {
    private:
        unsigned char &bit;

    public:
        BitProxy(unsigned char &bit) : bit(bit) {}

        BitProxy& operator=(unsigned char x) { bit = x; return *this; }
        operator unsigned char() const { return bit; }
    };

    BitProxy operator[](size_t index) { return BitProxy(bits[index]); }

    friend std::ostream& operator<< (std::ostream &output, const BitProxy &x)
    {
        output << static_cast<short>(static_cast<unsigned char>(x));
        return output;
    }
};

Bitset a;
// populate a as needed...
cout << a[x];
cout << 'a';

现场演示