运算符优先级

这几天一直在做YUV视频格式的解码，其中碰到一个计算错误，找了好久才找到原因，原来是一个运算符优先级的问题。运算式是这样A+B>>16，当然A和B都算是比较复杂的式子。我的原义是要先做右移运算，再做加法。结果由于没有注意到加法优先级比右移要高，实际上是先加法，再右移。所以那个运算的正确做法是A+(B>>16)。     找这个错误花了我将近一个小时的时间，为了以后不至于犯同样的错误，我特意在网上找个一份运算符优先级的表贴在这里，以便时刻提醒自己。另外关于YUV的解码问题，我过几天也整理一份，算作为自己的学习笔记。 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