C++优先级20150909

• 理解：

  1）一般的计算顺序：取值-》运算-》比较-》赋值

  2）取值运算永远最先执行（不取值如何做运算）要注意有++，–也是最先的

  3）取值：取反，++，负号，引用，去引用

  4）计算：* / + – ,移位，（中间插了一个比较）位运算

  Precedence	Operator	Description	Example	Associativity
  1	() [] -> . :: ++ –	Grouping operator Array access Member access from a pointer Member access from an object Scoping operator Post-increment Post-decrement	(a + b) / 4; array[4] = 2; ptr->age = 34; obj.age = 34; Class::age = 2; for( i = 0; i < 10; i++ ) … for( i = 10; i > 0; i– ) …	left to right
  2	! ~ ++ — – + * & (type) sizeof	Logical negation Bitwise complement Pre-increment Pre-decrement Unary minus Unary plus Dereference Address of Cast to a given type Return size in bytes	if( !done ) … flags = ~flags; for( i = 0; i < 10; ++i ) … for( i = 10; i > 0; –i ) … int i = -1; int i = +1; data = *ptr; address = &obj; int i = (int) floatNum; int size = sizeof(floatNum);	right to left
  3	->* .*	Member pointer selector Member pointer selector	ptr->*var = 24; obj.*var = 24;	left to right
  4	* / %	Multiplication Division Modulus	int i = 2 * 4; float f = 10 / 3; int rem = 4 % 3;	left to right
  5	+ -	Addition Subtraction	int i = 2 + 3; int i = 5 – 1;	left to right
  6	<< >>	Bitwise shift left Bitwise shift right	int flags = 33 << 1; int flags = 33 >> 1;	left to right
  7	< <= > >=	Comparison less-than Comparison less-than-or-equal-to Comparison greater-than Comparison geater-than-or-equal-to	if( i < 42 ) … if( i <= 42 ) … if( i > 42 ) … if( i >= 42 ) …	left to right
  8	== !=	Comparison equal-to Comparison not-equal-to	if( i == 42 ) … if( i != 42 ) …	left to right
  9	&	Bitwise AND	flags = flags & 42;	left to right
  10	^	Bitwise exclusive OR	flags = flags ^ 42;	left to right
  11	|	Bitwise inclusive (normal) OR	flags = flags | 42;	left to right
  12	&&	Logical AND	if( conditionA && conditionB ) …	left to right
  13	||	Logical OR	if( conditionA || conditionB ) …	left to right
  14	? :	Ternary conditional (if-then-else)	int i = (a > b) ? a : b;	right to left
  15	= += -= *= /= %= &= ^= |= <<= >>=	Assignment operator Increment and assign Decrement and assign Multiply and assign Divide and assign Modulo and assign Bitwise AND and assign Bitwise exclusive OR and assign Bitwise inclusive (normal) OR and assign Bitwise shift left and assign Bitwise shift right and assign	int a = b; a += 3; b -= 4; a *= 5; a /= 2; a %= 3; flags &= new_flags; flags ^= new_flags; flags |= new_flags; flags <<= 2; flags >>= 2;	right to left
  16	,	Sequential evaluation operator	for( i = 0, j = 0; i < 10; i++, j++ ) …	left to right