Think_in_CPP第十二章 操作符重载(2)
2012-09-15 08:59
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12.3 二元运算符(Binary operators)
12.3.1 全局函数方式
12.3.2 成员函数方式
12.3.3 要点备忘
1.operator=只允许成员函数方式。
2.所有的赋值操作符都要检查是否自赋值(self-assignment),但是在有的情况下是不需要的,比如A+=A。最需要检查此项的是operator=,尽管在某些情况下不检查也能得到想要的结果,但是建议在重载operator=的时候,检查是否是自赋值。
12.3.1 全局函数方式
class Integer { long i; public: Integer(long ll = 0) : i(ll) {} // Operators that create new, modified value: friend const Integer operator+(const Integer& left, const Integer& right); friend const Integer operator-(const Integer& left, const Integer& right); friend const Integer operator*(const Integer& left, const Integer& right); friend const Integer operator/(const Integer& left, const Integer& right); friend const Integer operator%(const Integer& left, const Integer& right); friend const Integer operator^(const Integer& left, const Integer& right); friend const Integer operator&(const Integer& left, const Integer& right); friend const Integer operator|(const Integer& left, const Integer& right); friend const Integer operator<<(const Integer& left, const Integer& right); friend const Integer operator>>(const Integer& left, const Integer& right); // Assignments modify & return lvalue: friend Integer& operator+=(Integer& left, const Integer& right); friend Integer& operator-=(Integer& left, const Integer& right); friend Integer& operator*=(Integer& left, const Integer& right); friend Integer& operator/=(Integer& left, const Integer& right); friend Integer& operator%=(Integer& left, const Integer& right); friend Integer& operator^=(Integer& left, const Integer& right); friend Integer& operator&=(Integer& left, const Integer& right); friend Integer& operator|=(Integer& left, const Integer& right); friend Integer& operator>>=(Integer& left, const Integer& right); friend Integer& operator<<=(Integer& left, const Integer& right); // Conditional operators return true/false: friend int operator==(const Integer& left, const Integer& right); friend int operator!=(const Integer& left, const Integer& right); friend int operator<(const Integer& left, const Integer& right); friend int operator>(const Integer& left, const Integer& right); friend int operator<=(const Integer& left, const Integer& right); friend int operator>=(const Integer& left, const Integer& right); friend int operator&&(const Integer& left, const Integer& right); friend int operator||(const Integer& left, const Integer& right); }; const Integer operator+(const Integer& left, const Integer& right) { return Integer(left.i + right.i); } const Integer operator-(const Integer& left, const Integer& right) { return Integer(left.i - right.i); } const Integer operator*(const Integer& left, const Integer& right) { return Integer(left.i * right.i); } const Integer operator/(const Integer& left, const Integer& right) { require(right.i != 0, "divide by zero"); return Integer(left.i / right.i); } const Integer operator%(const Integer& left, const Integer& right) { require(right.i != 0, "modulo by zero"); return Integer(left.i % right.i); } const Integer operator^(const Integer& left, const Integer& right) { return Integer(left.i ^ right.i); } const Integer operator&(const Integer& left, const Integer& right) { return Integer(left.i & right.i); } const Integer operator|(const Integer& left, const Integer& right) { return Integer(left.i | right.i); } const Integer operator<<(const Integer& left, const Integer& right) { return Integer(left.i << right.i); } const Integer operator>>(const Integer& left, const Integer& right) { return Integer(left.i >> right.i); } // Assignments modify & return lvalue: Integer& operator+=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i += right.i; return left; } Integer& operator-=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i -= right.i; return left; } Integer& operator*=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i *= right.i; return left; } Integer& operator/=(Integer& left, const Integer& right) { require(right.i != 0, "divide by zero"); if(&left == &right) {/* self-assignment */} left.i /= right.i; return left; } Integer& operator%=(Integer& left, const Integer& right) { require(right.i != 0, "modulo by zero"); if(&left == &right) {/* self-assignment */} left.i %= right.i; return left; } Integer& operator^=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i ^= right.i; return left; } Integer& operator&=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i &= right.i; return left; } Integer& operator|=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i |= right.i; return left; } Integer& operator>>=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i >>= right.i; return left; } Integer& operator<<=(Integer& left, const Integer& right) { if(&left == &right) {/* self-assignment */} left.i <<= right.i; return left; } // Conditional operators return true/false: int operator==(const Integer& left, const Integer& right) { return left.i == right.i; } int operator!=(const Integer& left, const Integer& right) { return left.i != right.i; } int operator<(const Integer& left, const Integer& right) { return left.i < right.i; } int operator>(const Integer& left, const Integer& right) { return left.i > right.i; } int operator<=(const Integer& left, const Integer& right) { return left.i <= right.i; } int operator>=(const Integer& left, const Integer& right) { return left.i >= right.i; } int operator&&(const Integer& left, const Integer& right) { return left.i && right.i; } int operator||(const Integer& left, const Integer& right) { return left.i || right.i; }
12.3.2 成员函数方式
class Byte { unsigned char b; public: Byte(unsigned char bb = 0) : b(bb) {} // No side effects: const member function: const Byte operator+(const Byte& right) const { return Byte(b + right.b); } const Byte operator-(const Byte& right) const { return Byte(b - right.b); } const Byte operator*(const Byte& right) const { return Byte(b * right.b); } const Byte operator/(const Byte& right) const { require(right.b != 0, "divide by zero"); return Byte(b / right.b); } const Byte operator%(const Byte& right) const { require(right.b != 0, "modulo by zero"); return Byte(b % right.b); } const Byte operator^(const Byte& right) const { return Byte(b ^ right.b); } const Byte operator&(const Byte& right) const { return Byte(b & right.b); } const Byte operator|(const Byte& right) const { return Byte(b | right.b); } const Byte operator<<(const Byte& right) const { return Byte(b << right.b); } const Byte operator>>(const Byte& right) const { return Byte(b >> right.b); } // Assignments modify & return lvalue. // operator= can only be a member function: Byte& operator=(const Byte& right) { // Handle self-assignment: if(this == &right) return *this; b = right.b; return *this; } Byte& operator+=(const Byte& right) { if(this == &right) {/* self-assignment */} b += right.b; return *this; } Byte& operator-=(const Byte& right) { if(this == &right) {/* self-assignment */} b -= right.b; return *this; } Byte& operator*=(const Byte& right) { if(this == &right) {/* self-assignment */} b *= right.b; return *this; } Byte& operator/=(const Byte& right) { require(right.b != 0, "divide by zero"); if(this == &right) {/* self-assignment */} b /= right.b; return *this; } Byte& operator%=(const Byte& right) { require(right.b != 0, "modulo by zero"); if(this == &right) {/* self-assignment */} b %= right.b; return *this; } Byte& operator^=(const Byte& right) { if(this == &right) {/* self-assignment */} b ^= right.b; return *this; } Byte& operator&=(const Byte& right) { if(this == &right) {/* self-assignment */} b &= right.b; return *this; } Byte& operator|=(const Byte& right) { if(this == &right) {/* self-assignment */} b |= right.b; return *this; } Byte& operator>>=(const Byte& right) { if(this == &right) {/* self-assignment */} b >>= right.b; return *this; } Byte& operator<<=(const Byte& right) { if(this == &right) {/* self-assignment */} b <<= right.b; return *this; } // Conditional operators return true/false: int operator==(const Byte& right) const { return b == right.b; } int operator!=(const Byte& right) const { return b != right.b; } int operator<(const Byte& right) const { return b < right.b; } int operator>(const Byte& right) const { return b > right.b; } int operator<=(const Byte& right) const { return b <= right.b; } int operator>=(const Byte& right) const { return b >= right.b; } int operator&&(const Byte& right) const { return b && right.b; } int operator||(const Byte& right) const { return b || right.b; } // Write the contents to an ostream: void print(std::ostream& os) const { os << "0x" << std::hex << int(b) << std::dec; } };
12.3.3 要点备忘
1.operator=只允许成员函数方式。
2.所有的赋值操作符都要检查是否自赋值(self-assignment),但是在有的情况下是不需要的,比如A+=A。最需要检查此项的是operator=,尽管在某些情况下不检查也能得到想要的结果,但是建议在重载operator=的时候,检查是否是自赋值。
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