操作符重载

以下表格为操作符重载推荐的使用方法

OPERATOR	NAME OR CATEGOTY	METHORD OR GLOBAL FUNCTION	WHEN TO OVERLOAD	SAMPLE PROTOTYPES
`operator+` `operator-` `operator*` `operator/` `operator%`	Binary arithmetic	Global function recommended	Whenever you want to provide these operations for your class	`T operator+(const T&, const T&);` `T operator+(const T&, const E&);`
`operator-` `operator+` `operator~`	Unary arithmetic and bitwise operators	Method recommended	Whenever you want to provide these operations for your class	`T operator-() const;`
`operator++` `operator--`	Pre-increment and pre-decrement	Method recommended	Whenever you overload += and -= taking an arithmetic argument (int, long, . . .)	`T& operator++();`
`operator++` `operator--`	Post-increment and post-decrement	Method recommended	Whenever you overload += and -= taking an arithmetic argument (int, long, . . .)	`T operator++(int);`
`operator=`	Assignment operator	Method recommended	Whenever your class has dynamically allocated resources, or members that are references	`T& operator= (const T&);`
`operator+=` `operator-=` `operator*=` `operator/=` `operator%=`	Shorthand arithmetic operator assignments	Method recommended	Whenever you overload the binary arithmetic operators and your class is not designed to be immutable	`T& operator+= (const T&);` `T& operator+= (const E&);`
`operator<<` `operator>>` `operator&` `operator	</li><li>operator^`</li></ul>	Binary bitwise operators	Global function recommended	Whenever you want to provide these operations	`T operator<< (const T&, const T&);` `T operator<< (const T&, const E&);`
`operator<<=` `operator>>=` `operator&=` `operator	=</li><li>operator^=`</li></ul>	Shorthand bitwise operator assignments	Method recommended	Whenever you overload the binary bitwise operators and your class is not designed to be immutable	`T& operator<<= (const T&);` `T& operator<<= (const E&);`
`operator<=>`	Three-way comparison operator	Method recommended	Whenever you want to provide comparison support for your class	`auto operator<=> (const T&) const;` `partial_ordering operator<=>(const E&) const;`
`operator==`	Binary equality operator	C++20: method recommended Pre-C++20: global function recommended	Whenever you want to provide comparison support for your class	`bool operator== (const T&) const;` `bool operator== (const E&) const;` `bool operator== (const T&, const T&);` `bool operator== (const T&, const E&);`
`operator!=`	Binary inequality operator	C++20: method recommended Pre-C++20: global function recommended	C++20: not needed as the compiler automatically provides != when you provide == Pre-C++20: Whenever you want to provide comparison support for your class	`bool operator!= (const T&) const;` `bool operator!= (const E&) const;` `bool operator!= (const T&, const T&);` `bool operator!= (const T&, const E&);`
`operator<` `operator>` `operator<=` `operator>=`	Binary comparison operators	Global function recommended	Whenever you want to provide these operations	`bool operator< (const T&, const T&);` `bool operator< (const T&, const E&);`
`operator<<` `operator>>`	I/O stream operators (insertion and extraction)	Global function required	Whenever you want to provide these operations	`ostream& operator<< (ostream&, const T&);` `istream& operator>> (istream&, T&);`
`operator!`	Boolean negation operator	Method recommended	Rarely; use bool or void* conversion instead	`bool operator!() const;`
`operator&&` `operator		`</li></ul>	Binary Boolean operators	Global function recommended	Rarely, if ever, because you lose short-circuiting; it’s better to overload & and	instead, as these never short-circuit	`bool operator&&(const T&, const T&);`
`operator[]`	Subscripting (array index) operator	Method required	When you want to support subscripting	`E& operator[](size_t);` `const E& operator[] (size_t) const;`
`operator()`	Function call operator	Method required	When you want objects to behave like function pointers, or for multidimensional array access, since [] can have only one index	Return type and parameters can vary; see later examples in this chapter
`operator type()`	Conversion, or cast, operators (separate operator for each type)	Method required	When you want to provide conversions from your class to other types	`operator double() const;`
`operator ""_x`	User-defined literal operator	Global function required	When you want to support user-defined literals	`T operator""_i(long double d);`
`operator new` `operator new[]`	Memory allocation routines	Method recommended	When you want to control memory allocation for your classes (rarely)	`void* operator new(size_t size);` `void* operator new[](size_t size);`
`operator delete` `operator delete[]`	Memory deallocation routines	Method recommended	Whenever you overload the memory allocation routines (rarely)	`void operator delete(void* ptr) noexcept;` `void operator delete[](void* ptr) noexcept;`
`operator*` `operator->`	Dereferencing operators	Method recommended for operator* Method required for operator->	Useful for smart pointers	`E& operator*() const;` `E* operator->() const;`

操作符优先级

• 以下表格中 T 代表类型，x, y, z 代表对象

PRECEDENCE	OPERATOR	ASSOCIATIVITY
1	::	Left-to-right
2	x++, x--, x(), x[], T(), T{}, ., ->	Left-to-right
3	++x, --x, +x, -x, !, ~, *x, &x, (T), sizeof, co_await, new, delete, new[], delete[]	Right-to-left
4	.*, ->*	Left-to-right
5	x*y, x/y, x%y	Left-to-right
6	x+y, x-y	Left-to-right
7	<<, >>	Left-to-right
8	<=>	Left-to-right
9	<, <=, >, >=	Left-to-right
10	==, !=	Left-to-right
11	&	Left-to-right
12	^	Left-to-right
13	`	`	Left-to-right
14	&&	Left-to-right
15	`		`	Left-to-right
16	x?y:z, throw, co_yield, =, +=, -=, *=, /=, %=, <<=, >>=, &=, ^=, `	=`	Right-to-left
17	,	Left-to-right