Operators in C and C++

Template:Short description Template:Use American English Template:Use dmy dates This is a list of operators in the C and C++ programming languages.

All listed operators are in C++ and lacking indication otherwise, in C as well. Some tables include a "In C" column that indicates whether an operator is also 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.

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

Many operators specified by a sequence of symbols are commonly referred to by a name that consists of the name of each symbol. For example, += and -= are often called "plus equal(s)" and "minus equal(s)", instead of the more verbose "assignment by addition" and "assignment by subtraction".

Operators

In the following tables, lower case letters such as a and b represent literal values, object/variable names, or l-values, as appropriate. R, S and T stand for a data type, and K for a class or enumeration type. Some operators have alternative spellings using digraphs and trigraphs or operator synonyms.

Arithmetic

C and C++ have the same arithmetic operators and all can be overloaded in C++.

Operation		Syntax	C++ prototype
			in class K	outside class
Template:Rh colspan="2" | Addition	Template:Nowrap	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Subtraction	a - b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Unary plus; integer promotion	+a	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Unary minus; additive inverse	-a	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Multiplication	a * b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Division	a / b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Modulo<ref name="modulo" group="lower-alpha" />	a % b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Prefix increment	++a	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Postfix increment	a++	Template:CppTemplate:Efn	Template:CppTemplate:Efn
Template:Rh colspan="2" | Prefix decrement	--a	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Postfix decrement	a--	Template:CppTemplate:Efn	Template:CppTemplate:Efn

Relational

All relational (comparison) operators can be overloaded in C++. Since C++20, the inequality operator is automatically generated if operator== is defined and all four relational operators are automatically generated if operator<=> is defined.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Operation		Syntax	In C	C++ prototype
				in class K	outside class
Template:Rh colspan="2" | Equal to	a == b	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Not equal to	a != b	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Greater than	a > b	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Less than	a < b	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Greater than or equal to	a >= b	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Less than or equal to	a <= b	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Three-way comparison<ref name="threewaycomparison" group="lower-alpha"/>Template:Efn	a <=> b	Template:No	Template:Cpp	Template:Cpp

Logical

C and C++ have the same logical operators and all can be overloaded in C++.

Note that overloading logical AND and OR is discouraged, because as overloaded operators they always evaluate both operands instead of providing the normal semantics of short-circuit evaluation.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Operation		Syntax	C++ prototype
			in class K	outside class
Template:Rh colspan="2" | NOT	!a	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | AND	a && b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | OR	a || b	<syntaxhighlight lang="cpp" class="" style="" inline="1">bool K::operator Template:!!(S b);</syntaxhighlight>	<syntaxhighlight lang="cpp" class="" style="" inline="1">bool operator Template:!!(K a, S b);</syntaxhighlight>

Bitwise

C and C++ have the same bitwise operators and all can be overloaded in C++.

Operation		Syntax	C++ prototype
			in class K	outside class
Template:Rh colspan="2" | NOT	~a	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | AND	a & b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | OR	a | b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | XOR	a ^ b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Shift left<ref name="bitshift" group="lower-alpha" />	a << b	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Shift right<ref name="bitshift" group="lower-alpha" />Template:Refn	a >> b	Template:Cpp	Template:Cpp

Assignment

C and C++ have the same assignment operators and all can be overloaded in C++.

For the combination operators, a ⊚= b (where ⊚ represents an operation) is equivalent to a = a ⊚ b, except that a is evaluated only once.

Operation	Syntax	C++ prototype
		in class K	outside class
Template:Rh | Assignment	Template:Nowrap	Template:Cpp	Template:N/a
Template:Rh | Addition combination	a += b	Template:Cpp	Template:Cpp
Template:Rh | Subtraction combination	a -= b	Template:Cpp	Template:Cpp
Template:Rh | Multiplication combination	a *= b	Template:Cpp	Template:Cpp
Template:Rh | Division combination	a /= b	Template:Cpp	Template:Cpp
Template:Rh | Modulo combination	a %= b	Template:Cpp	Template:Cpp
Template:Rh | Bitwise AND combination	a &= b	Template:Cpp	Template:Cpp
Template:Rh | Bitwise OR combination	a |= b	Template:Cpp	Template:Cpp
Template:Rh | Bitwise XOR combination	a ^= b	Template:Cpp	Template:Cpp
Template:Rh | Bitwise left shift combination	a <<= b	Template:Cpp	Template:Cpp
Template:Rh | Bitwise right shift combinationTemplate:Refn	a >>= b	Template:Cpp	Template:Cpp

Member and pointer

Operation		Syntax	Can overload	In C	C++ prototype
					in class K	outside class
Template:Rh colspan="2" | Subscript	a[b]a<:b:><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>	Template:Yes	Template:Yes	Template:Cpp Template:Cpp<ref name="sinceCXX23" group="lower-alpha" />	Template:N/a
Template:Rh colspan="2" | Indirection Template:Small	*a	Template:Yes	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Address-of Template:Small	&a	Template:Yes<ref name="addressof2" group="lower-alpha"/>	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Structure dereference Template:Small	a->b	Template:Yes	Template:Yes	Template:Cpp<ref name="arrowptr" group="lower-alpha" />	Template:N/a
Template:Rh colspan="2" | Structure reference Template:Small	a.b	Template:No	Template:Yes	Template:Rh colspan="2" Template:N/a
Template:Rh colspan="2" | Member selected by pointer-to-member b of object pointed to by a<ref name="arrowstar" group="lower-alpha" />	a->*b	Template:Yes	Template:No	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Member of object a selected by pointer-to-member b	a.*b	Template:No	Template:No	Template:Rh colspan="2" Template:N/a

Other

Operation		Syntax	Can overload	In C	C++ prototype
					in class K	outside class
Template:Rh colspan="2" | Function call	a(a1, a2)	Template:Yes	Template:Yes	Template:Cpp	Template:N/a
Template:Rh colspan="2" | Comma	a, b	Template:Yes	Template:Yes	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Ternary conditional	a ? b : c	Template:No	Template:Yes	colspan="2" Template:N/a
Template:Rh colspan="2" | Scope resolution	a::b<ref name="scopal" group="lower-alpha" />	Template:No	Template:No	colspan="2" Template:N/a
Template:Rh colspan="2" | User-defined literals<ref name="ud-literal" group="lower-alpha" /><ref name="sinceCXX11" group="lower-alpha" />	"a"_b	Template:Yes	Template:No	Template:N/a	Template:Cpp
Template:Rh colspan="2" | Sizeof	sizeof a<ref name="sizeof" group="lower-alpha" /> sizeof (R)	Template:No	Template:Yes	colspan="2" Template:N/a
Template:Rh colspan="2" | Size of parameter pack<ref name="sinceCXX11" group="lower-alpha" />	sizeof...(Args)	Template:No	Template:No	colspan="2" Template:N/a
Template:Rh colspan="2" | Alignof<ref name="sinceCXX11" group="lower-alpha" />	alignof(R) or _Alignof(R)<ref name="alignof" group="lower-alpha"/>	Template:No	Template:Yes	colspan="2" Template:N/a
Template:Rh colspan="2" | Decltype<ref name="sinceCXX11" group="lower-alpha" />	decltype (a) decltype (R)	Template:No	Template:No	colspan="2" Template:N/a
Template:Rh colspan="2" | Type identification	typeid(a) typeid(R)	Template:No	Template:No	colspan="2" Template:N/a
Template:Rh colspan="2" | Conversion Template:Small	(R)a	Template:Yes	Template:Yes	Template:Cpp<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>	Template:N/a
Template:Rh colspan="2" | ConversionTemplate:Efn<ref>Explicit type conversion in C++</ref>	R(a) R{a}<ref name="sinceCXX11" group="lower-alpha" /> auto(a)<ref name="sinceCXX23" group="lower-alpha" /> auto{a}<ref name="sinceCXX23" group="lower-alpha" />	Template:No	Template:No	Template:Rh colspan="2" Template:N/a
Template:Rh colspan="2" | static_cast conversionTemplate:Efn	static_cast<R>(a)	Template:Yes	Template:No	Template:Cpp Template:Cpp<ref name="sinceCXX11" group="lower-alpha" />	Template:N/a
Template:Rh colspan="2" | dynamic cast conversion	dynamic_cast<R>(a)	Template:No	Template:No	colspan="2" Template:N/a
Template:Rh colspan="2" | const_cast conversion	const_cast<R>(a)	Template:No	Template:No	colspan="2" Template:N/a
Template:Rh colspan="2" | reinterpret_cast conversion	reinterpret_cast<R>(a)	Template:No	Template:No	colspan="2" Template:N/a
Template:Rh colspan="2" | Allocate storage	new R<ref name="infer" group="lower-alpha"/>	Template:Yes	Template:No	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Allocate array	new R[n]<ref name="infer2" group="lower-alpha"/>	Template:Yes	Template:No	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Deallocate storage	delete a	Template:Yes	Template:No	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Deallocate array	delete[] a	Template:Yes	Template:No	Template:Cpp	Template:Cpp
Template:Rh colspan="2" | Exception check<ref name="sinceCXX11" group="lower-alpha" />	noexcept(a)	Template:No	Template:No	colspan="2" Template:N/a

Synonyms

C++ defines keywords to act as aliases for a number of operators:<ref name="Committee">Template:Cite book</ref>

Keyword	Operator
<syntaxhighlight lang="text" class="" style="" inline="1">and</syntaxhighlight>	&&
<syntaxhighlight lang="text" class="" style="" inline="1">and_eq</syntaxhighlight>	&=
<syntaxhighlight lang="text" class="" style="" inline="1">bitand</syntaxhighlight>	&
<syntaxhighlight lang="text" class="" style="" inline="1">bitor</syntaxhighlight>	|
<syntaxhighlight lang="text" class="" style="" inline="1">compl</syntaxhighlight>	~
<syntaxhighlight lang="text" class="" style="" inline="1">not</syntaxhighlight>	!
<syntaxhighlight lang="text" class="" style="" inline="1">not_eq</syntaxhighlight>	!=
<syntaxhighlight lang="text" class="" style="" inline="1">or</syntaxhighlight>	||
<syntaxhighlight lang="text" class="" style="" inline="1">or_eq</syntaxhighlight>	|=
<syntaxhighlight lang="text" class="" style="" inline="1">xor</syntaxhighlight>	^
<syntaxhighlight lang="text" class="" style="" inline="1">xor_eq</syntaxhighlight>	^=

Each keyword is a different way to specify an operator and as such can be used instead of the corresponding symbolic variation. For example, <syntaxhighlight lang="text" class="" style="" inline="1">(a > 0 and not flag)</syntaxhighlight> and <syntaxhighlight lang="text" class="" style="" inline="1">(a > 0 && !flag)</syntaxhighlight> specify the same behavior. As another example, the bitand keyword may be used to replace not only the bitwise-and operator but also the address-of operator, and it can be used to specify reference types (e.g., <syntaxhighlight lang="text" class="" style="" inline="1">int bitand ref = n</syntaxhighlight>).

The ISO C specification makes allowance for these keywords as preprocessor macros in the header file <syntaxhighlight lang="text" class="" style="" inline="1">iso646.h</syntaxhighlight>. For compatibility with C, C++ also provides the header <syntaxhighlight lang="text" class="" style="" inline="1">iso646.h</syntaxhighlight>, the inclusion of which has no effect. Until C++20, it also provided the corresponding header <syntaxhighlight lang="text" class="" style="" inline="1">ciso646</syntaxhighlight> which had no effect as well.

Expression evaluation order

During expression evaluation, the order in which sub-expressions are evaluated is determined by precedence and associativity. An operator with higher precedence is evaluated before a operator of lower precedence and the operands of an operator are evaluated based on associativity. The following table describes the precedence and associativity of the C and C++ operators. Operators are shown in groups of equal precedence with groups ordered in descending precedence from top to bottom (lower order is higher precedence).<ref>Template:Cite book</ref><ref>Template:Cite tech report</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Operator precedence is not affected by overloading.

Order	Operator	Description	Associativity
1 highest	::	Scope resolution (C++ only)	None
2	++	Postfix increment	Left-to-right
	--	Postfix 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	Right-to-left
	--	Prefix decrement
	+	Unary plus
	-	Unary minus
	!	Logical NOT
	~	Bitwise NOT (ones' complement)
	(type)	Type cast
	*	Indirection (dereference)
	&	Address-of
	sizeof	Sizeof
	_Alignof	Alignment requirement (since C11)
	new, new[]	Dynamic memory allocation (C++ only)
	delete, delete[]	Dynamic memory deallocation (C++ only)
4	.*	Pointer to member (C++ only)	Left-to-right
	->*	Pointer to member (C++ only)
5	*	Multiplication	Left-to-right
	/	Division
	%	Modulo (remainder)
6	+	Addition	Left-to-right
	-	Subtraction
7	<<	Bitwise left shift	Left-to-right
	>>	Bitwise right shift
8	<=>	Three-way comparison (Introduced in C++20 - C++ only)	Left-to-right
9	<	Less than	Left-to-right
	<=	Less than or equal to
	>	Greater than
	>=	Greater than or equal to
10	==	Equal to	Left-to-right
	!=	Not equal to
11	&	Bitwise AND	Left-to-right
12	^	Bitwise XOR (exclusive or)	Left-to-right
13	|	Bitwise OR (inclusive or)	Left-to-right
14	&&	Logical AND	Left-to-right
15	||	Logical OR	Left-to-right
16	co_await	Coroutine processing (C++ only)	Right-to-left
	co_yield
17	?:	Ternary conditional operator	Right-to-left
	=	Direct assignment
	+=	Assignment by sum
	-=	Assignment by difference
	*=	Assignment by product
	/=	Assignment by quotient
	%=	Assignment by remainder
	<<=	Assignment by bitwise left shift
	>>=	Assignment by bitwise right shift
	&=	Assignment by bitwise AND
	^=	Assignment by bitwise XOR
	|=	Assignment by bitwise OR
	throw	Throw operator (exceptions throwing, C++ only)
18 lowest	,	Comma	Left-to-right

Details

Although this table is adequate for describing most evaluation order, it does not describe a few details. 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). So, the expression in the middle of the conditional operator (between ? and :) is parsed as if parenthesized. Also, the immediate, un-parenthesized 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).

Chained expressions

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

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

File:Precedence 2.png

Precedence and bindings

• Abstracting the issue of precedence or binding, consider the diagram above for the expression 3+2*y[i]++. 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 is 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 postfix ++ (the ( . )++ operator acts only after y[i] is evaluated in the expression).

Binding

The binding of operators in C and C++ is specified 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: <syntaxhighlight lang="c">logical-OR-expression ? expression : conditional-expression</syntaxhighlight> while in C++ it is: <syntaxhighlight lang="cpp">logical-OR-expression ? expression : assignment-expression</syntaxhighlight> Hence, the expression: <syntaxhighlight lang="text">e = a < d ? a++ : a = d</syntaxhighlight> is parsed differently in the two languages. In C, this expression is a syntax error, because the syntax for an assignment expression in C is: <syntaxhighlight lang="c">unary-expression '=' assignment-expression</syntaxhighlight> In C++, it is parsed as: <syntaxhighlight lang="cpp">e = (a < d ? a++ : (a = d))</syntaxhighlight> which is a valid expression.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

To use the comma operator in a function call argument expression, variable assignment, or a comma-separated list, use of parentheses is required.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> For example,

<syntaxhighlight lang="cpp"> int a = 1, b = 2, weirdVariable = (++a, b), d = 4; </syntaxhighlight>

Criticism of bitwise and equality operators precedence

The precedence of the bitwise logical operators has been criticized.<ref name="Bell">Template:Citation.</ref> Conceptually, & and | are arithmetic operators like * and +.

The expression Template:Cpp is syntactically parsed as Template:Cpp whereas the expression Template:Cpp is parsed as Template:Cpp. This requires parentheses to be used more often than they otherwise would.

Historically, there was no syntactic distinction between the bitwise and logical operators. In BCPL, B and early C, the operators Template:Cpp didn't exist. Instead Template:Cpp had different meaning depending on whether they are used in a 'truth-value context' (i.e. when a Boolean value was expected, for example in Template:Cpp it behaved as a logical operator, but in Template:Cpp it behaved as a bitwise one). It was retained so as to keep backward compatibility with existing installations.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Moreover, in C++ (and later versions of C) equality operations, with the exception of the three-way comparison operator, yield bool type values which are conceptually a single bit (1 or 0) and as such do not properly belong in "bitwise" operations.

See also

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External links

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• C Operator Precedence
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