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C/C++ 运算符优先级和结合性

先看下C的运算符优先级和结合性:

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C Operator Precedence and Associativity

C Programming (COP-2220)


This page lists C operators in order of precedence (highest to lowest). Their associativityindicates in what order operators of equal precedence in an expression are applied.


Operator

Description

Associativity

()
[]
.
->
++  --
Parentheses (function call) (see Note 1)
Brackets (array subscript)
Member selection via object name
Member selection via pointer
Postfix increment/decrement (see Note 2)

left-to-right

++  --
+  -
!  ~
(type)
*
&
sizeof
 
 
Prefix increment/decrement
Unary plus/minus
Logical negation/bitwise complement
Cast (change type)
Dereference
Address
Determine size in bytes
right-to-left
*  /  % Multiplication/division/modulus left-to-right
+  - Addition/subtraction left-to-right
<<  >> Bitwise shift left, Bitwise shift right left-to-right
<  <=
>  >=
Relational less than/less than or equal to
Relational greater than/greater than or equal to
left-to-right
==  != Relational is equal to/is not equal to left-to-right
& Bitwise AND left-to-right
^ Bitwise exclusive OR left-to-right
| Bitwise inclusive OR left-to-right
&& Logical AND left-to-right
|| Logical OR left-to-right
?: Ternary conditional right-to-left
=
+=  -=
*=  /=
%=  &=
^=  |=
<<=  >>=
Assignment
Addition/subtraction assignment
Multiplication/division assignment
Modulus/bitwise AND assignment
Bitwise exclusive/inclusive OR assignment
Bitwise shift left/right assignment
right-to-left

,

Comma (separate expressions) left-to-right
Note 1:
Parentheses are also used to group sub-expressions to force a different precedence; such parenthetical expressions can be nested and are evaluated from inner to outer.
Note 2:
Postfix increment/decrement have high precedence, but the actual increment or decrement of the operand is delayed (to be accomplished sometime before the statement completes execution). So in the statement y = x * z++; the current value of z is used to evaluate the expression (i.e., z++ evaluates to z) and z only incremented after all else is done. Seepostinc.c for another example.

 

再看下wikipedia上的一个C和CPP一起的运算符的优先级和结合行,原文还分别对算术运算符(Arithmetic operators)、比较/关系运算符(Comparison operators/Relational operators)、逻辑运算符(Logical operators)、位运算符(Bitwise operators)、复合赋值符运算符(Compound assignment operators)、成员和指针操作符(Member and pointer operators)进行了比较,还是很详细的。摘录如下:

Operators in C and C++

This is a list of operators in the C and C++ programming languages. All the operators listed exist in C++; the fourth column "Included in C", dictates whether an operator is also present in C. Note that C does not support operator overloading.

When not overloaded, for the operators &&, ||, and , (the comma operator), there is a sequence point after the evaluation of the first operand.

C++ also contains the type conversion operators const_cast, static_cast, dynamic_cast, and reinterpret_cast which are not listed in the table for brevity. The formatting of these operators means that their precedence level is unimportant.

Most of the operators available in C and C++ are also available in other languages such as C#, Java, Perl, and PHP with the same precedence, associativity, and semantics.


Table

For the purposes of this table, a, b, and c represent valid values (literals, values from variables, or return value), object names, or lvalues, as appropriate.

Overloadable means that the operator is overloadable in C++. "Included in C" means that the operator exists and has a semantic meaning in C (operators are not overloadable in C).

Arithmetic operators

Operator name Syntax Overloadable Included
in C
Prototype examples (T is any type)
As member of T Outside class definitions
Basic assignment a<span class="Apple-converted-space"> </span><b>=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator =(const T&b); N/A
Addition a<span class="Apple-converted-space"> </span><b>+</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator +(const T& b)const; ​T operator +(const T& a,const T& b);
Subtraction a<span class="Apple-converted-space"> </span><b>-</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator -(const T& b)const; ​T operator -(const T& a,const T& b);
Unary plus (integer promotion) <b>+</b>a Yes Yes ​T T::operator +() const; ​T operator +(const T& a);
Unary minus (additive inverse) <b>-</b>a Yes Yes ​T T::operator -() const; ​T operator -(const T& a);
Multiplication a<span class="Apple-converted-space"> </span><b>*</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator *(const T& b)const; ​T operator *(const T &a,const T& b);
Division a<span class="Apple-converted-space"> </span><b>/</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator /(const T& b)const; ​T operator /(const T& a,const T& b);
Modulo (remainder) a<span class="Apple-converted-space"> </span><b>%</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator %(const T& b)const; ​T operator %(const T& a,const T& b);
Increment Prefix <b>++</b>a Yes Yes ​T& T::operator ++(); ​T& operator ++(T& a);
Suffix a<b>++</b> Yes Yes ​T T::operator ++(int); ​T operator ++(T& a, int);
Note: C++ uses the unnamed dummy-parameter int to differentiate between prefix and suffix increment operators.
Decrement Prefix <b>--</b>a Yes Yes ​T& T::operator --(); ​T& operator --(T& a);
Suffix a<b>--</b> Yes Yes ​T T::operator --(int); ​T operator --(T& a, int);
Note: C++ uses the unnamed dummy-parameter int to differentiate between prefix and suffix decrement operators.

Comparison operators/Relational operators

Operator name Syntax Overloadable Included
in C
Prototype examples (T is any type)
As member of T Outside class definitions
Equal to a<span class="Apple-converted-space"> </span><b>==</b>b Yes Yes bool T::operator ==(const T&b) const; bool operator ==(const T& a,const T& b);
Not equal to a<span class="Apple-converted-space"> </span><b>!=</b>b Yes Yes bool T::operator !=(const T&b) const; bool operator !=(const T& a,const T& b);
Greater than a<span class="Apple-converted-space"> </span><b>></b><span class="Apple-converted-space"> </span>b Yes Yes bool T::operator >(const T&b) const; bool operator >(const T& a,const T& b);
Less than a<span class="Apple-converted-space"> </span><b><</b><span class="Apple-converted-space"> </span>b Yes Yes bool T::operator <(const T&b) const; bool operator <(const T& a,const T& b);
Greater than or equal to a<span class="Apple-converted-space"> </span><b>>=</b>b Yes Yes bool T::operator >=(const T&b) const; bool operator >=(const T& a,const T& b);
Less than or equal to a<span class="Apple-converted-space"> </span><b><=</b>b Yes Yes bool T::operator <=(const T&b) const; bool operator <=(const T& a,const T& b);

Logical operators

Operator name Syntax Overloadable Included
in C
Prototype examples (T is any type)
As member of T Outside class definitions
Logical negation (NOT) <b>!</b>a Yes Yes bool T::operator !() const; bool operator !(const T& a);
Logical AND a<span class="Apple-converted-space"> </span><b>&&</b>b Yes Yes bool T::operator &&(const T&b) const; bool operator &&(const T& a,const T& b);
Logical OR a<span class="Apple-converted-space"> </span><b>||</b>b Yes Yes bool T::operator ||(const T&b) const; bool operator ||(const T& a,const T& b);

Bitwise operators

Operator name Syntax Overloadable Included
in C
Prototype examples (T is any type)
As member of T Outside class definitions
Bitwise NOT <b>~</b>a Yes Yes ​T T::operator ~() const; ​T operator ~(const T& a);
Bitwise AND a<span class="Apple-converted-space"> </span><b>&</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator &(const T& b)const; ​T operator &(const T& a, constT& b);
Bitwise OR a<span class="Apple-converted-space"> </span><b>|</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator |(const T& b)const; ​T operator |(const T& a, constT& b);
Bitwise XOR a<span class="Apple-converted-space"> </span><b>^</b><span class="Apple-converted-space"> </span>b Yes Yes ​T T::operator ^(const T& b)const; ​T operator ^(const T& a, constT& b);
Bitwise left shift[note 1] a<span class="Apple-converted-space"> </span><b><<</b>b Yes Yes ​T T::operator <<(const T& b)const; ​T operator <<(const T& a, constT& b);
Bitwise right shift[note 1] a<span class="Apple-converted-space"> </span><b>>></b>b Yes Yes ​T T::operator >>(const T& b)const; ​T operator >>(const T& a, constT& b);

Compound assignment operators

Operator name Syntax Overloadable Included
in C
Prototype examples (T is any type)
As member of T Outside class definitions
Addition assignment a<span class="Apple-converted-space"> </span><b>+=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator +=(const T&b); ​T& operator +=(T& a, const T&b);
Subtraction assignment a<span class="Apple-converted-space"> </span><b>-=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator -=(const T&b); ​T& operator -=(T& a, const T&b);
Multiplication assignment a<span class="Apple-converted-space"> </span><b>*=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator *=(const T&b); ​T& operator *=(T& a, const T&b);
Division assignment a<span class="Apple-converted-space"> </span><b>/=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator /=(const T&b); ​T& operator /=(T& a, const T&b);
Modulo assignment a<span class="Apple-converted-space"> </span><b>%=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator %=(const T&b); ​T& operator %=(T& a, const T&b);
Bitwise AND assignment a<span class="Apple-converted-space"> </span><b>&=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator &=(const T&b); ​T& operator &=(T& a, const T&b);
Bitwise OR assignment a<span class="Apple-converted-space"> </span><b>|=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator |=(const T&b); ​T& operator |=(T& a, const T&b);
Bitwise XOR assignment a<span class="Apple-converted-space"> </span><b>^=</b><span class="Apple-converted-space"> </span>b Yes Yes ​T& T::operator ^=(const T&b); ​T& operator ^=(T& a, const T&b);
Bitwise left shift assignment a<span class="Apple-converted-space"> </span><b><<=</b>b Yes Yes ​T& T::operator <<=(constT& b); ​T& operator <<=(T& a, constT& b);
Bitwise right shift assignment a<span class="Apple-converted-space"> </span><b>>>=</b>b Yes Yes ​T& T::operator >>=(constT& b); ​T& operator >>=(T& a, constT& b);

Member and pointer operators

Operator name Syntax Overloadable Included
in C
Prototype examples (T, T2 and R are any type)
As member of T Outside class definitions
Array subscript a<b>[</b>b<b>]</b> Yes Yes ​R& T::operator [](constT2& b); N/A
Indirection ("object pointed to by a") <b>*</b>a Yes Yes ​R& T::operator *(); ​R& operator *(T&a);
Reference ("address of a") <b>&</b>a Yes Yes ​T* T::operator &(); ​T* operator &(T&a);
Member b of object pointed to by a a<b>-></b>b Yes Yes ​R* T::operator ->(); N/A
Member b of object a a<b>.</b>b No Yes N/A
Member pointed to by b of object pointed to by a[note 2] a<b>->*</b>b Yes No ​R T::operator->*(R);[note 3] ​R operator->*(T, R);[note 3]
Member pointed to by b of object a a<b>.*</b>b No No N/A

Other operators

Operator name Syntax Overloadable Included
in C
Prototype examples (T, R, Arg1 and Arg2 are any type)
As member of T Outside class definitions
Function call
See Function object.
a<b>(</b>a1, a2<b>)</b> Yes Yes ​R T::operator ()(Arg1 a1, Arg2 a2, …); N/A
Comma a<b>,</b><span class="Apple-converted-space"> </span>b Yes Yes ​R& T::operator ,(R& b)const; ​R& operator ,(const T&a, R& b);
Ternary conditional a<span class="Apple-converted-space"> </span><b>?</b><span class="Apple-converted-space"> </span>b<span class="Apple-converted-space"> </span><b>:</b><span class="Apple-converted-space"> </span>c No Yes N/A
Scope resolution a<b>::</b>b No No N/A
Size-of <b>sizeof</b>(a)[note 4]
<b>sizeof</b>(<i>type</i>)
No Yes N/A
Type identification <b>typeid</b>(a)
<b>typeid</b>(<i>type</i>)
No No N/A
Cast (<i>type</i>) a Yes Yes ​T::operator R() const; N/A
Note: for user-defined conversions, the return type implicitly and necessarily matches the operator name.
Allocate storage <b>new</b><span class="Apple-converted-space"> </span><i>type</i> Yes No void* T::operator new(size_tx); void* operatornew(size_t x);
Allocate storage (array) <b>new</b><span class="Apple-converted-space"> </span><i>type</i><b>[</b>n<b>]</b> Yes No void* T::operatornew[](size_t x); void* operatornew[](size_t x);
Deallocate storage <b>delete</b><span class="Apple-converted-space"> </span>a Yes No void T::operatordelete(void* x); void operatordelete(void* x);
Deallocate storage (array) <b>delete[]</b><span class="Apple-converted-space"> </span>a Yes No void T::operatordelete[](void* x); void operatordelete[](void* x);

Notes:

  1. ^ a b In the context of iostreams, writers often will refer to << and >> as the “put-to” or "stream insertion" and “get-from” or "stream extraction" operators, respectively.
  2. ^ An example can be found in "Implementing operator->* for Smart Pointers" by Scott Meyers.
  3. ^ a b In the case where the ->* operator is to work just like the default implementation, the R parameter will be method pointer to a method of the class T and the return value must be some kind of functor object that is ready to be called with (only) the method parameters.
  4. ^ The parentheses are not necessary when taking the size of a value, only when taking the size of a type. However, they are usually used regardless.

Operator precedence

The following is a table that lists the precedence and associativity of all the operators in the C and C++ languages (when the operators also exist in Java, Perl, PHP and many other recent languages, the precedence is the same as that given). Operators are listed top to bottom, in descending precedence. Descending precedence refers to the priority of evaluation. Considering an expression, an operator which is listed on some row will be evaluated prior to any operator that is listed on a row further below it. 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. An operator's precedence is unaffected by overloading.

The syntax of expressions in C and C++ is specified by a context-free grammar.[citation needed] The table given here has been inferred from the grammar.[citation needed] For the ISO C 1999 standard, section 6.5.6 note 71 states that the C grammar provided by the specification defines the precedence of the C operators, and also states that the operator precedence resulting from the grammar closely follows the specification's section ordering:

"The [C] syntax [i.e., grammar] specifies the precedence of operators in the evaluation of an expression, which is the same as the order of the major subclauses of this subclause, highest precedence first."

A precedence table, while mostly adequate, cannot resolve a few details. In particular, note that the ternary operator allows any arbitrary expression as its middle operand, despite being listed as having higher precedence than the assignment and comma operators. Thus a ? b , c : d is interpreted as a ? (b, c) : d, and not as the meaningless (a ? b), (c : d). Also, note that the immediate, unparenthesized result of a C cast expression cannot be the operand of sizeof. Therefore, sizeof (int) * x is interpreted as(sizeof(int)) * x and not sizeof ((int) *x).

Precedence Operator Description Associativity
1 :: Scope resolution (C++ only) Left-to-right
2 ++ -- Suffix/postfix increment and decrement
() Function call
[] Array subscripting
. Element selection by reference
-> Element selection through pointer
typeid() Run-time type information (C++ only) (see typeid)
const_cast Type cast (C++ only) (see const cast)
dynamic_cast Type cast (C++ only) (see dynamic_cast)
reinterpret_cast Type cast (C++ only) (see reinterpret cast)
static_cast Type cast (C++ only) (see static cast)
3 ++ -- Prefix increment and decrement Right-to-left
+ - Unary plus and minus
! ~ Logical NOT and bitwise NOT
(<i>type</i>) Type cast
* Indirection (dereference)
& Address-of
sizeof Size-of
new, new[] Dynamic memory allocation (C++ only)
delete, delete[] Dynamic memory deallocation (C++ only)
4 .* ->* Pointer to member (C++ only) Left-to-right
5 * / % Multiplication, division, and modulus (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 (see ?:) Right-to-Left
16 = 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
17 throw Throw operator (exceptions throwing, C++ only)
18 , Comma Left-to-right

Notes

The precedence table determines the order of binding in chained expressions, when it is not expressly specified by parentheses.

  • For example, <font color="#0000ff">++x*3</font> is ambiguous without some precedence rule(s). The precedence table tells us that: x is 'bound' more tightly to ++than to *, so that whatever ++ does (now or later—see below), it does it ONLY to x (and not to <font color="#0000ff">x*3</font>); it is equivalent to (<font color="#0000ff">++x</font>, <font color="#0000ff">x*3</font>).
  • Similarly, with <font color="#0000ff">3*x++</font>, where though the post-fix ++ is designed to act AFTER the entire expression is evaluated, the precedence table makes it clear that ONLY x gets incremented (and NOT <font color="#0000ff">3*x</font>); it is functionally equivalent to something like (<font color="#0000ff">tmp=3*x</font>, <font color="#0000ff">x++</font>, <font color="#0000ff">tmp</font>) withtmp being a temporary value.

Precedence and bindings

  </div>

  <ul style="padding-bottom: 0px; line-height: 1.5em; list-style-type: square; margin: 0.3em 0px 0.5em 1.5em; padding-left: 0px; padding-right: 0px; list-style-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAANCAYAAABhPKSIAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAACtJREFUeF7NjbEJAAAIw7zRu/w5ouBUBEeHDM2QGiA8kObBULuFcJbSXN8T78SqnpKltAIAAAAASUVORK5CYII=); padding-top: 0px">
    <li style="margin-bottom: 0.1em">
      Abstracting the issue of precedence or binding, consider the diagram above. The compiler's job is to resolve the diagram into an expression, one in which several unary operators ( call them 3+( . ), 2*( . ), ( . )++ and ( . )[ i ] ) are competing to bind to y. The order of precedence table resolves the final sub-expression they each act upon: ( . )[ i ] acts only on y, ( . )++ acts only on y[i], 2*( . ) acts only on y[i]++ and 3+( . ) acts 'only' on 2*((y[i])++). It's important to note that WHAT sub-expression gets acted on by each operator is clear from the precedence table but WHEN each operator acts is not resolved by the precedence table; in this example, the ( . )++ operator acts only on y[i] by the precedence rules but binding levels alone do not indicate the timing of the Suffix ++ (the ( . )++ operator acts only after y[i] is evaluated in the expression).
    </li>
  </ul>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    Many of the operators containing multi-character sequences are given "names" built from the operator name of each character. For example,<code style="background-color: rgb(249,249,249); font-family: monospace, &#39;Courier New&#39;">+=</code><span class="Apple-converted-space">&#160;</span>and<span class="Apple-converted-space">&#160;</span><code style="background-color: rgb(249,249,249); font-family: monospace, &#39;Courier New&#39;">-=</code><span class="Apple-converted-space">&#160;</span>are often called<span class="Apple-converted-space">&#160;</span><i>plus equal(s)</i><span class="Apple-converted-space">&#160;</span>and<span class="Apple-converted-space">&#160;</span><i>minus equal(s)</i>, instead of the more verbose "assignment by addition" and "assignment by subtraction".
  </p>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    The binding of operators in C and C++ is specified (in the corresponding Standards) by a factored language grammar, rather than a precedence table. This creates some subtle conflicts. For example, in C, the syntax for a conditional expression is:
  </p>

  <div style="border-bottom: rgb(47,111,171) 1px dashed; text-align: left; border-left: rgb(47,111,171) 1px dashed; padding-bottom: 1em; line-height: 1.1em; background-color: rgb(249,249,249); padding-left: 1em; padding-right: 1em; color: black; border-top: rgb(47,111,171) 1px dashed; border-right: rgb(47,111,171) 1px dashed; padding-top: 1em" dir="ltr" class="mw-geshi">
    <div style="line-height: normal; font-family: monospace" class="c source-c">
      <pre style="background-image: none; border-bottom: white 0px; border-left: white 0px; padding-bottom: 0px; margin: 0px; padding-left: 0px; padding-right: 0px; font: 1em/1.2em monospace; color: black; vertical-align: top; border-top: white 0px; border-right: white 0px; padding-top: 0px; background-origin: initial; background-clip: initial" class="de1">logical<span style="color: rgb(51,153,51)" class="sy0">-</span>OR<span style="color: rgb(51,153,51)" class="sy0">-</span>expression <span style="color: rgb(51,153,51)" class="sy0">?</span> expression <span style="color: rgb(51,153,51)" class="sy0">:</span> conditional<span style="color: rgb(51,153,51)" class="sy0">-</span>expression</pre></p>
    </div></p>
  </div>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    while in C++ it is:
  </p>

  <div style="border-bottom: rgb(47,111,171) 1px dashed; text-align: left; border-left: rgb(47,111,171) 1px dashed; padding-bottom: 1em; line-height: 1.1em; background-color: rgb(249,249,249); padding-left: 1em; padding-right: 1em; color: black; border-top: rgb(47,111,171) 1px dashed; border-right: rgb(47,111,171) 1px dashed; padding-top: 1em" dir="ltr" class="mw-geshi">
    <div style="line-height: normal; font-family: monospace" class="cpp source-cpp">
      <pre style="background-image: none; border-bottom: white 0px; border-left: white 0px; padding-bottom: 0px; margin: 0px; padding-left: 0px; padding-right: 0px; font: 1em/1.2em monospace; color: black; vertical-align: top; border-top: white 0px; border-right: white 0px; padding-top: 0px; background-origin: initial; background-clip: initial" class="de1">logical<span style="color: rgb(0,0,64)" class="sy2">-</span>OR<span style="color: rgb(0,0,64)" class="sy2">-</span>expression <span style="color: rgb(0,128,128)" class="sy4">?</span> expression <span style="color: rgb(0,128,128)" class="sy4">:</span> assignment<span style="color: rgb(0,0,64)" class="sy2">-</span>expression</pre></p>
    </div></p>
  </div>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    Hence, the expression:
  </p>

  <div style="border-bottom: rgb(47,111,171) 1px dashed; text-align: left; border-left: rgb(47,111,171) 1px dashed; padding-bottom: 1em; line-height: 1.1em; background-color: rgb(249,249,249); padding-left: 1em; padding-right: 1em; color: black; border-top: rgb(47,111,171) 1px dashed; border-right: rgb(47,111,171) 1px dashed; padding-top: 1em" dir="ltr" class="mw-geshi">
    <div style="line-height: normal; font-family: monospace" class="text source-text">
      <pre style="background-image: none; border-bottom: white 0px; border-left: white 0px; padding-bottom: 0px; margin: 0px; padding-left: 0px; padding-right: 0px; font: 1em/1.2em monospace; color: black; vertical-align: top; border-top: white 0px; border-right: white 0px; padding-top: 0px; background-origin: initial; background-clip: initial" class="de1">e = a &lt; d ? a++ : a = d</pre></p>
    </div></p>
  </div>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    is parsed differently in the two languages. In C, this expression is a syntax error, but many compilers parse it as:
  </p>

  <div style="border-bottom: rgb(47,111,171) 1px dashed; text-align: left; border-left: rgb(47,111,171) 1px dashed; padding-bottom: 1em; line-height: 1.1em; background-color: rgb(249,249,249); padding-left: 1em; padding-right: 1em; color: black; border-top: rgb(47,111,171) 1px dashed; border-right: rgb(47,111,171) 1px dashed; padding-top: 1em" dir="ltr" class="mw-geshi">
    <div style="line-height: normal; font-family: monospace" class="c source-c">
      <pre style="background-image: none; border-bottom: white 0px; border-left: white 0px; padding-bottom: 0px; margin: 0px; padding-left: 0px; padding-right: 0px; font: 1em/1.2em monospace; color: black; vertical-align: top; border-top: white 0px; border-right: white 0px; padding-top: 0px; background-origin: initial; background-clip: initial" class="de1">e <span style="color: rgb(51,153,51)" class="sy0">=</span> <span style="color: rgb(0,153,0)" class="br0">(</span><span style="color: rgb(0,153,0)" class="br0">(</span>a <span style="color: rgb(51,153,51)" class="sy0">&lt;</span> d <span style="color: rgb(51,153,51)" class="sy0">?</span> a<span style="color: rgb(51,153,51)" class="sy0">++</span> <span style="color: rgb(51,153,51)" class="sy0">:</span> a<span style="color: rgb(0,153,0)" class="br0">)</span> <span style="color: rgb(51,153,51)" class="sy0">=</span> d<span style="color: rgb(0,153,0)" class="br0">)</span></pre></p>
    </div></p>
  </div>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    which is a semantic error, since the result of the conditional-expression (which might be<span class="Apple-converted-space">&#160;</span><i>a++</i>) is not an lvalue. In C++, it is parsed as:
  </p>

  <div style="border-bottom: rgb(47,111,171) 1px dashed; text-align: left; border-left: rgb(47,111,171) 1px dashed; padding-bottom: 1em; line-height: 1.1em; background-color: rgb(249,249,249); padding-left: 1em; padding-right: 1em; color: black; border-top: rgb(47,111,171) 1px dashed; border-right: rgb(47,111,171) 1px dashed; padding-top: 1em" dir="ltr" class="mw-geshi">
    <div style="line-height: normal; font-family: monospace" class="cpp source-cpp">
      <pre style="background-image: none; border-bottom: white 0px; border-left: white 0px; padding-bottom: 0px; margin: 0px; padding-left: 0px; padding-right: 0px; font: 1em/1.2em monospace; color: black; vertical-align: top; border-top: white 0px; border-right: white 0px; padding-top: 0px; background-origin: initial; background-clip: initial" class="de1">e <span style="color: rgb(0,0,128)" class="sy1">=</span> <span style="color: rgb(0,128,0)" class="br0">(</span>a <span style="color: rgb(0,0,128)" class="sy1">&lt;</span> d <span style="color: rgb(0,128,128)" class="sy4">?</span> a<span style="color: rgb(0,0,64)" class="sy2">++</span> <span style="color: rgb(0,128,128)" class="sy4">:</span> <span style="color: rgb(0,128,0)" class="br0">(</span>a <span style="color: rgb(0,0,128)" class="sy1">=</span> d<span style="color: rgb(0,128,0)" class="br0">)</span><span style="color: rgb(0,128,0)" class="br0">)</span></pre></p>
    </div></p>
  </div>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    which is a valid expression.
  </p>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    The precedence of the bitwise logical operators has been criticized.[1]<span class="Apple-converted-space">&#160;</span>Conceptually, & and | are arithmetic operators like + and *.
  </p>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    The expression<span class="Apple-converted-space">&#160;</span><span style="line-height: normal; font-family: monospace" class="mw-geshi cpp source-cpp">​a<span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,64)" class="sy3">&</span><span class="Apple-converted-space">&#160;</span>b<span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,128)" class="sy1">==</span><span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,221)" class="nu0">7</span>​</span><span class="Apple-converted-space">&#160;</span>is syntactically parsed as<span class="Apple-converted-space">&#160;</span><span style="line-height: normal; font-family: monospace" class="mw-geshi cpp source-cpp">​a<span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,64)" class="sy3">&</span><span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,128,0)" class="br0">(</span>b<span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,128)" class="sy1">==</span><span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,221)" class="nu0">7</span><span style="color: rgb(0,128,0)" class="br0">)</span>​</span><span class="Apple-converted-space">&#160;</span>whereas the expression<span class="Apple-converted-space">&#160;</span><span style="line-height: normal; font-family: monospace" class="mw-geshi cpp source-cpp">​a<span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,64)" class="sy2">+</span><span class="Apple-converted-space">&#160;</span>b<span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,128)" class="sy1">==</span><span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,221)" class="nu0">7</span>​</span><span class="Apple-converted-space">&#160;</span>is parsed as<span class="Apple-converted-space">&#160;</span><span style="line-height: normal; font-family: monospace" class="mw-geshi cpp source-cpp">​<span style="color: rgb(0,128,0)" class="br0">(</span>a<span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,64)" class="sy2">+</span><span class="Apple-converted-space">&#160;</span>b<span style="color: rgb(0,128,0)" class="br0">)</span><span class="Apple-converted-space">&#160;</span><span style="color: rgb(0,0,128)" class="sy1">==</span><span style="color: rgb(0,0,221)" class="nu0">7</span>​</span>. This requires parentheses to be used more often than they otherwise would.
  </p>

  <h3 style="background-image: none; border-bottom-style: none; padding-bottom: 0.17em; overflow-x: hidden; overflow-y: hidden; margin: 0px 0px 0.3em; width: auto; color: black; font-size: 17px; font-weight: bold; padding-top: 0.5em; background-origin: initial; background-clip: initial">
    <span id="C.2B.2B_operator_synonyms" class="mw-headline">C++ operator synonyms</span>
  </h3>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    C++ defines<sup style="line-height: 1em; font-style: normal; font-weight: normal" id="cite_ref-4" class="reference"><a style="background-image: none; white-space: nowrap; color: rgb(6,69,173); text-decoration: none; background-origin: initial; background-clip: initial" href="http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#cite_note-4"><span>[</span>1<span>]</span></a></sup><span class="Apple-converted-space">&#160;</span>keywords to act as aliases for a number of operators:<span class="Apple-converted-space">&#160;</span><code style="background-color: rgb(249,249,249); font-family: monospace, &#39;Courier New&#39;">and (&&), bitand (&), and_eq (&=), or (||), bitor (|), or_eq (|=), xor (^), xor_eq (^=), not (!), not_eq (!=), compl (~)</code>. These can be used exactly the same way as the symbols they replace as they are not the same operator under a different name, but rather simple text aliases for the<span class="Apple-converted-space">&#160;</span><i>name</i><span class="Apple-converted-space">&#160;</span>(character string) of respective operator. For instance,<span class="Apple-converted-space">&#160;</span><code style="background-color: rgb(249,249,249); font-family: monospace, &#39;Courier New&#39;">bitand</code><span class="Apple-converted-space">&#160;</span>may be used to replace not only the bitwise operator but also the address-of operator, and it can even be used to specify reference types (e.g. int bitand ref = n;).
  </p>

  <p style="line-height: 1.5em; margin: 0.4em 0px 0.5em">
    The ANSI C specification makes allowance for these keywords as preprocessor macros in the header file <a style="background-image: none; color: rgb(6,69,173); text-decoration: none; background-origin: initial; background-clip: initial" title="Iso646.h" href="http://en.wikipedia.org/wiki/Iso646.h">iso646.h</a>. For compatibility with C, C++ provides the header <a style="background-image: none; color: rgb(6,69,173); text-decoration: none; background-origin: initial; background-clip: initial" class="mw-redirect" title="Ciso646" href="http://en.wikipedia.org/wiki/Ciso646">ciso646</a>, inclusion of which has no effect.
  </p>

  <h2 style="background-image: none; border-bottom: rgb(170,170,170) 1px solid; padding-bottom: 0.17em; overflow-x: hidden; overflow-y: hidden; margin: 0px 0px 0.6em; width: auto; color: black; font-size: 19px; font-weight: normal; padding-top: 0.5em; background-origin: initial; background-clip: initial">
    <span id="References" class="mw-headline">References</span>
  </h2>

  <div style="list-style-type: decimal; font-size: 12px" class="reflist">
    <ol style="padding-bottom: 0px; line-height: 1.5em; margin: 0.3em 0px 0.5em 3.2em; padding-left: 0px; padding-right: 0px; font-size: 12px; list-style-image: none; padding-top: 0px" class="references">
      <li style="margin-bottom: 0.1em" id="cite_note-4">
        <b><a style="background-image: none; color: rgb(6,69,173); text-decoration: none; background-origin: initial; background-clip: initial" href="http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#cite_ref-4">^</a></b><span class="Apple-converted-space">&#160;</span><span style="word-wrap: break-word" class="citation book">ISO/IEC JTC1/SC22/WG21 - The C++ Standards Committee<span class="Apple-converted-space">&#160;</span>(1 September 1998).<span class="Apple-converted-space">&#160;</span><i>ISO/IEC 14882:1998(E) Programming Language C++</i>. International standardization working group for the programming language C++. pp. 40–41.</span>
      </li>
    </ol>
  </div>

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