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12、C++操作符優(yōu)先級(jí):
記憶方法：
去掉一個(gè)最高的，去掉一個(gè)最低的，剩下的是一、二、三、賦值;雙目運(yùn)算符中，順序?yàn)樗阈g(shù)、關(guān)系和邏輯，移位和邏輯位插入其中。
--摘自《C語言程序設(shè)計(jì)實(shí)用問答》
問題：如何記住運(yùn)算符的15種優(yōu)先級(jí)和結(jié)合性?
解答：C語言中運(yùn)算符種類比較繁多，優(yōu)先級(jí)有15種，結(jié)合性有兩種。
如何記憶兩種結(jié)合性和15種優(yōu)先級(jí)?下面講述一種記憶方法。
結(jié)合性有兩種，一種是自左至右，另一種是自右至左，大部分運(yùn)算符的結(jié)合性是自左至右，只有單目運(yùn)算符、三目運(yùn)算符的賦值運(yùn)算符的結(jié)合性自右至左。
優(yōu)先級(jí)有15種，記憶方法如下：
記住一個(gè)最高的：構(gòu)造類型的元素或成員以及小括號(hào)。
記住一個(gè)最低的：逗號(hào)運(yùn)算符。
剩余的是一、二、三、賦值——意思是單目、雙目、三目和賦值運(yùn)算符。
在諸多運(yùn)算符中，又分為：算術(shù)、關(guān)系、邏輯。
兩種位操作運(yùn)算符中，移位運(yùn)算符在算術(shù)運(yùn)算符后邊，邏輯位運(yùn)算符在邏輯運(yùn)算符的前面。
再細(xì)分如下：
算術(shù)運(yùn)算符*，/，%高于+，-。
關(guān)系運(yùn)算符中：>，>=，<和<=高于==，!=。
邏輯運(yùn)算符中，除了邏輯求反(!)是單目外，邏輯與(&&)高于邏輯或(||)。
邏輯位運(yùn)算符中，除了邏輯按位求反(~)外，按位與(&)高于按位半加(^)，高于按位或(|)。
| Prece dence | Operator | Description | Example | Over loadable | Associativity |
| 1 | :: | Scope resolution operator | Class::age = 2; | no | left to right |
| 2 | () | Function call | printf(“Hello world\n”); | yes | left to right |
| () | Member initalization | c_tor(int x, int y) : _x(x), _y(y * 10) {} | yes | ||
| [] | Array access | array[4] = 2; | yes | ||
| -> | Member access from a pointer | ptr->age = 34; | yes | ||
| . | Member access from an object | obj.age = 34; | no | ||
| ++ | Post-increment | for (int i = 0; i < 10; i++) cout << i; | yes | ||
| -- | Post-decrement | for (int i = 10; i > 0; i--) cout << i; | yes | ||
| dynamic_cast | Runtime-checked type conversion | Y& y = dynamic_cast<Y&>(x); | no | ||
| static_cast | Unchecked type conversion | Y& y = static_cast<Y&>(x); | no | ||
| reinterpret_cast | Reinterpreting type conversion | int const* p = reinterpret_cast<int const*>(0x1234); | no | ||
| const_cast | Cast away/Add constness | int* q = const_cast<int*>(p); | no | ||
| typeid | Get type information | std::type_info const& t = typeid(x); | no | ||
| 3 | ! | Logical negation | if (!done) ... | yes | right to left |
| not | Alternate spelling for ! | ||||
| ~ | Bitwise complement | flags = ~flags; | yes | ||
| compl | Alternate spelling for ~ | ||||
| ++ | Pre-increment | for (i = 0; i < 10; ++i) cout << i; | yes | ||
| -- | Pre-decrement | for (i = 10; i > 0; --i) cout << i; | yes | ||
| - | Unary minus | int i = -1; | yes | ||
| + | Unary plus | int i = +1; | yes | ||
| * | Dereference | int data = *intPtr; | yes | ||
| & | Address of | int *intPtr = &data; | yes | ||
| sizeof | Size (of the type) of the operand in bytes | size_t s = sizeof(int); | no | ||
| new | Dynamic memory allocation | long* pVar = new long; | yes | ||
| new [] | Dynamic memory allocation of array | long* array = new long[20]; | yes | ||
| delete | Deallocating the memory | delete pVar; | yes | ||
| delete [] | Deallocating the memory of array | delete [] array; | yes | ||
| (type) | Cast to a given type | int i = (int)floatNum; | yes | ||
| 4 | ->* | Member pointer selector | ptr->*var = 24; | yes | left to right |
| .* | Member object selector | obj.*var = 24; | no | ||
| 5 | * | Multiplication | int i = 2 * 4; | yes | left to right |
| / | Division | float f = 10.0 / 3.0; | yes | ||
| % | Modulus | int rem = 4 % 3; | yes | ||
| 6 | + | Addition | int i = 2 + 3; | yes | left to right |
| - | Subtraction | int i = 5 - 1; | yes | ||
| 7 | << | Bitwise shift left | int flags = 33 << 1; | yes | left to right |
| >> | Bitwise shift right | int flags = 33 >> 1; | yes | ||
| 8 | < | Comparison less-than | if (i < 42) ... | yes | left to right |
| <= | Comparison less-than-or-equal-to | if (i <= 42) ... | yes | ||
| > | Comparison greater-than | if (i > 42) ... | yes | ||
| >= | Comparison greater-than-or-equal-to | if (i >= 42) ... | yes | ||
| 9 | == | Comparison equal-to | if (i == 42) ... | yes | left to right |
| eq | Alternate spelling for == | ||||
| != | Comparison not-equal-to | if (i != 42) ... | yes | ||
| not_eq | Alternate spelling for != | ||||
| 10 | & | Bitwise AND | flags = flags & 42; | yes | left to right |
| bitand | Alternate spelling for & | ||||
| 11 | ^ | Bitwise exclusive OR (XOR) | flags = flags ^ 42; | yes | left to right |
| xor | Alternate spelling for ^ | ||||
| 12 | | | Bitwise inclusive (normal) OR | flags = flags | 42; | yes | left to right |
| bitor | Alternate spelling for | | ||||
| 13 | && | Logical AND | if (conditionA && conditionB) ... | yes | left to right |
| and | Alternate spelling for && | ||||
| 14 | || | Logical OR | if (conditionA || conditionB) ... | yes | left to right |
| or | Alternate spelling for || | ||||
| 15 | ? : | Ternary conditional (if-then-else) | int i = a > b ? a : b; | no | right to left |
| 16 | = | Assignment operator | int a = b; | yes | right to left |
| += | Increment and assign | a += 3; | yes | ||
| -= | Decrement and assign | b -= 4; | yes | ||
| *= | Multiply and assign | a *= 5; | yes | ||
| /= | Divide and assign | a /= 2; | yes | ||
| %= | Modulo and assign | a %= 3; | yes | ||
| &= | Bitwise AND and assign | flags &= new_flags; | yes | ||
| and_eq | Alternate spelling for &= | ||||
| ^= | Bitwise exclusive or (XOR) and assign | flags ^= new_flags; | yes | ||
| xor_eq | Alternate spelling for ^= | ||||
| |= | Bitwise normal OR and assign | flags |= new_flags; | yes | ||
| or_eq | Alternate spelling for |= | ||||
| <<= | Bitwise shift left and assign | flags <<= 2; | yes | ||
| >>= | Bitwise shift right and assign | flags >>= 2; | yes | ||
| 17 | throw | throw exception | throw EClass(“Message”); | no | |
| 18 | , | Sequential evaluation operator | for (i = 0, j = 0; i < 10; i++, j++) ... | yes | left to right |
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