C和C++的運算符優先級

C++ Operator Precedence

 

C++

 

C++ language

 

Expressions

 

The following table lists the precedence and associativity of C++ operators. Operators are listed top to bottom, in descending precedence.

http://en.cppreference.com/w/cpp/language/operator_precedence

Precedence	Operator	Description	Associativity
1	::	Scope resolution	Left-to-right
2	++   --	Suffix/postfix increment and decrement
	type() type{}	Function-style type cast
	()	Function call
	[]	Array subscripting
	.	Element selection by reference
	->	Element selection through pointer
3	++   --	Prefix increment and decrement	Right-to-left
	+   -	Unary plus and minus
	!   ~	Logical NOT and bitwise NOT
	(type)	C-style type cast
	*	Indirection (dereference)
	&	Address-of
	sizeof	Size-of[note 1]
	new, new[]	Dynamic memory allocation
	delete, delete[]	Dynamic memory deallocation
4	.*   ->*	Pointer to member	Left-to-right
5	*   /   %	Multiplication, division, and remainder
6	+   -	Addition and subtraction
7	<<   >>	Bitwise left shift and right shift
8	<   <=	For relational operators < and ≤ respectively
	>   >=	For relational operators > and ≥ respectively
9	==   !=	For relational = and ≠ respectively
10	&	Bitwise AND
11	^	Bitwise XOR (exclusive or)
12	|	Bitwise OR (inclusive or)
13	&&	Logical AND
14	||	Logical OR
15	?:	Ternary conditional[note 2]	Right-to-left
	=	Direct assignment (provided by default for C++ classes)
	+=   -=	Assignment by sum and difference
	*=   /=   %=	Assignment by product, quotient, and remainder
	<<=   >>=	Assignment by bitwise left shift and right shift
	&=   ^=   |=	Assignment by bitwise AND, XOR, and OR
16	throw	Throw operator (for exceptions)
17	,	Comma	Left-to-right

1. ↑ The operand of sizeof can't be a C-style type cast: the expression sizeof (int) * p is unambiguously interpreted as (sizeof(int)) * p, but not sizeof((int)*p).
2. ↑ The expression in the middle of the conditional operator (between ? and :) is parsed as if parenthesized: its precedence relative to ?: is ignored.

When parsing an expression, an operator which is listed on some row will be bound tighter (as if by parentheses) to its arguments than any operator that is listed on a row further below it. For example, the expressions std::cout<<a&band *p++ are parsed as (std::cout<<a)&b and *(p++), and not as std::cout<<(a&b) or (*p)++.

Operators that are in the same cell (there may be several rows of operators listed in a cell) are evaluated with the same precedence, in the given direction. For example, the expression a=b=c is parsed as a=(b=c), and not as (a=b)=c because of right-to-left associativity.

Operator precedence is unaffected by operator overloading.

Notes

Precedence and associativity are independent from order of evaluation.

The standard itself doesn't specify precedence levels. They are derived from the grammar.

const_cast, static_cast, dynamic_cast, reinterpret_cast, typeid, sizeof..., noexcept and alignof are not included since they are never ambiguous.

Some of the operators have alternate spellings (e.g., and for &&, or for ||, not for !, etc.).

Relative precedence of the conditional and assignment operators differs between C and C++: in C, assignment is not allowed on the right hand side of a conditional operator, so e = a < d ? a++ : a = d cannot be parsed. Many C compilers use a modified grammar where ?: has higher precedence than =, which parses that as e = ( ((a < d) ? (a++) : a) = d ) (which then fails to compile because ?: is never lvalue in C and = requires lvalue on the left). In C++, ?: and = have equal precedence and group right-to-left, so that e = a < d ? a++ : a = d parses as e = ((a < d) ? (a++) : (a = d)).

See also

Common operators
assignment	increment decrement	arithmetic	logical	comparison	member access	other
a = b a += b a -= b a *= b a /= b a %= b a &= b a |= b a ^= b a <<= b a >>= b	++a --a a++ a--	+a -a a + b a - b a * b a / b a % b ~a a & b a | b a ^ b a << b a >> b	!a a && b a || b	a == b a != b a < b a > b a <= b a >= b	a[b] *a &a a->b a.b a->*b a.*b	a(...) a, b (type) a ? :
Special operators
static_cast converts one type to another compatible type  dynamic_cast converts virtual base class to derived class const_cast converts type to compatible type with different cv qualifiers reinterpret_cast converts type to incompatible type new allocates memory delete deallocates memory sizeof queries the size of a type sizeof... queries the size of a parameter pack (since C++11) typeid queries the type information of a type noexcept checks if an expression can throw an exception (since C++11) alignof queries alignment requirements of a type (since C++11)