Operators in C and C++

Short description: Similar syntax in both computer languages

This is a list of operators in the C and C++ programming languages. All the operators (except typeof) listed exist in C++; the column "Included in C", states 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. 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 C-family languages such as C#, D, Java, Perl, and PHP with the same precedence, associativity, and semantics.

Table

For the purposes of these tables, a, b, and c represent valid values (literals, values from variables, or return value), object names, or lvalues, as appropriate. R, S and T stand for any type(s), and K for a class type or enumerated type.

Arithmetic operators

All arithmetic operators exist in C and C++ and can be overloaded in C++.

Operator name		Syntax	C++ prototype examples
			As member of K	Outside class definitions
Addition		a + b	R K::operator +(S b);	R operator +(K a, S b);
Subtraction		a - b	R K::operator -(S b);	R operator -(K a, S b);
Unary plus (integer promotion)		+a	R K::operator +();	R operator +(K a);
Unary minus (additive inverse)		-a	R K::operator -();	R operator -(K a);
Multiplication		a * b	R K::operator *(S b);	R operator *(K a, S b);
Division		a / b	R K::operator /(S b);	R operator /(K a, S b);
Modulo (integer remainder)		a % b	R K::operator %(S b);	R operator %(K a, S b);
Increment	Prefix	++a	R& K::operator ++();	R& operator ++(K& a);
	Postfix	a++	R K::operator ++(int);	R operator ++(K& a, int);
			Note: C++ uses the unnamed dummy-parameter int to differentiate between prefix and postfix increment operators.
Decrement	Prefix	--a	R& K::operator --();	R& operator --(K& a);
	Postfix	a--	R K::operator --(int);	R operator --(K& a, int);
			Note: C++ uses the unnamed dummy-parameter int to differentiate between prefix and postfix decrement operators.

Comparison operators/relational operators

All 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.

Operator name		Syntax	Included in C	Prototype examples
				As member of K	Outside class definitions
Equal to		a == b	Yes	bool K::operator ==(S const& b) const;	bool operator ==(K const& a, S const& b);
Not equal to		a != b a not_eq b	Yes	bool K::operator !=(S const& b) const;	bool operator !=(K const& a, S const& b);
Greater than		a > b	Yes	bool K::operator >(S const& b) const;	bool operator >(K const& a, S const& b);
Less than		a < b	Yes	bool K::operator <(S const& b) const;	bool operator <(K const& a, S const& b);
Greater than or equal to		a >= b	Yes	bool K::operator >=(S const& b) const;	bool operator >=(K const& a, S const& b);
Less than or equal to		a <= b	Yes	bool K::operator <=(S const& b) const;	bool operator <=(K const& a, S const& b);
Three-way comparison		a <=> b	No	auto K::operator <=>(const S &b);	auto operator <=>(const K &a, const S &b);
				The operator has a total of 3 possible return types: std::weak_ordering, std::strong_ordering and std::partial_ordering to which they all are convertible to.

Logical operators

All logical operators exist in C and C++ and can be overloaded in C++, albeit the overloading of the logical AND and logical OR is discouraged, because as overloaded operators they behave as ordinary function calls, which means that both of their operands are evaluated, so they lose their well-used and expected short-circuit evaluation property.

Operator name		Syntax	C++ prototype examples
			As member of K	Outside class definitions
Logical negation (NOT)		!a not a	bool K::operator !();	bool operator !(K a);
Logical AND		a && b a and b	bool K::operator &&(S b);	bool operator &&(K a, S b);
Logical OR		a || b a ??!??! b a or b	bool K::operator ||(S b);	bool operator ||(K a, S b);

Bitwise operators

All bitwise operators exist in C and C++ and can be overloaded in C++.

Operator name		Syntax	Prototype examples
			As member of K	Outside class definitions
Bitwise NOT		~a ??-a compl a	R K::operator ~();	R operator ~(K a);
Bitwise AND		a & b a bitand b	R K::operator &(S b);	R operator &(K a, S b);
Bitwise OR		a | b a ??! b a bitor b	R K::operator |(S b);	R operator |(K a, S b);
Bitwise XOR		a ^ b a ??' b a xor b	R K::operator ^(S b);	R operator ^(K a, S b);
Bitwise left shift		a << b	R K::operator <<(S b);	R operator <<(K a, S b);
Bitwise right shift		a >> b	R K::operator >>(S b);	R operator >>(K a, S b);

Assignment operators

All assignment expressions exist in C and C++ and can be overloaded in C++.

For the given operators the semantic of the built-in combined assignment expression a ⊚= b is equivalent to a = a ⊚ b, except that a is evaluated only once.

Operator name	Syntax	C++ prototype examples
		As member of K	Outside class definitions
Direct assignment	a = b	R& K::operator =(S b);	N/A
Addition assignment	a += b	R& K::operator +=(S b);	R& operator +=(K& a, S b);
Subtraction assignment	a -= b	R& K::operator -=(S b);	R& operator -=(K& a, S b);
Multiplication assignment	a *= b	R& K::operator *=(S b);	R& operator *=(K& a, S b);
Division assignment	a /= b	R& K::operator /=(S b);	R& operator /=(K& a, S b);
Modulo assignment	a %= b	R& K::operator %=(S b);	R& operator %=(K& a, S b);
Bitwise AND assignment	a &= b a and_eq b	R& K::operator &=(S b);	R& operator &=(K& a, S b);
Bitwise OR assignment	a |= b a ??!= b a or_eq b	R& K::operator |=(S b);	R& operator |=(K& a, S b);
Bitwise XOR assignment	a ^= b a ??'= b a xor_eq b	R& K::operator ^=(S b);	R& operator ^=(K& a, S b);
Bitwise left shift assignment	a <<= b	R& K::operator <<=(S b);	R& operator <<=(K& a, S b);
Bitwise right shift assignment	a >>= b	R& K::operator >>=(S b);	R& operator >>=(K& a, S b);

Member and pointer operators

Operator name		Syntax	Can overload in C++	Included in C	C++ prototype examples
					As member of K	Outside class definitions
Subscript		a[b] a<:b:> a??(b??)	Yes	Yes	R& K::operator [](S b); R& K::operator [](S b, ...); // since C++23	N/A
Indirection ("object pointed to by a")		*a	Yes	Yes	R& K::operator *();	R& operator *(K a);
Address-of ("address of a")		&a bitand a	Yes	Yes	R* K::operator &();	R* operator &(K a);
Structure dereference ("member b of object pointed to by a")		a->b	Yes	Yes	R* K::operator ->();	N/A
Structure reference ("member b of object a")		a.b	No	Yes	N/A
Member selected by pointer-to-member b of object pointed to by a		a->*b	Yes	No	R& K::operator ->*(S b);	R& operator ->*(K a, S b);
Member of object a selected by pointer-to-member b		a.*b	No	No	N/A

Other operators

Operator name		Syntax	Can overload in C++	Included in C	Prototype examples
					As member of K	Outside class definitions
Function call See Function object.		a(a1, a2)	Yes	Yes	R K::operator ()(S a, T b, ...);	N/A
Comma		a, b	Yes	Yes	R K::operator ,(S b);	R operator ,(K a, S b);
Ternary conditional		a ? b : c	No	Yes	N/A
Scope resolution		a::b	No	No	N/A
User-defined literals since C++11		"a"_b	Yes	No	N/A	R operator "" _b(T a)
Sizeof		sizeof a sizeof (R)	No	Yes	N/A
Size of parameter pack since C++11		sizeof...(Args)	No	No	N/A
Alignof since C++11		alignof(R) or _Alignof(R)	No	Yes	N/A
Typeof since C23		typeof (a) typeof (R) typeof_unqual (a) typeof_unqual (R)	N/A	Only	N/A
Decltype since C++11		decltype (a) decltype (R)	No	No	N/A
Type identification		typeid(a) typeid(R)	No	No	N/A
Conversion (C-style cast)		(R)a	Yes	Yes	K::operator R();	N/A
Conversion		R(a) R{a}since C++11 auto(a)since C++23 auto{a}since C++23	No	No	Note: behaves like const_cast/static_cast/reinterpret_cast. In the last two cases the auto specifier is replaced with the type of the invented variable x declared with auto x(a); (which is never interpreted as a function declaration) or auto x{a};, respectively.
static cast conversion		static_cast<R>(a)	Yes	No	K::operator R(); explicit K::operator R(); since C++11	N/A
					Note: for user-defined conversions, the return type implicitly and necessarily matches the operator name unless the type is inferred (e.g. operator auto() , operator decltype(auto)() etc.).
dynamic cast conversion		dynamic_cast<R>(a)	No	No	N/A
const cast conversion		const_cast<R>(a)	No	No	N/A
reinterpret cast conversion		reinterpret_cast<R>(a)	No	No	N/A
Allocate storage		new R	Yes	No	void* K::operator new(size_t x);	void* operator new(size_t x);
Allocate storage (array)		new R[n] new R<:n:> new R??(n??)	Yes	No	void* K::operator new[](size_t a);	void* operator new[](size_t a);
Deallocate storage		delete a	Yes	No	void K::operator delete(void* a);	void operator delete(void* a);
Deallocate storage (array)		delete[] a delete<::> a delete??(??) a	Yes	No	void K::operator delete[](void* a);	void operator delete[](void* a);
Exception check since C++11		noexcept(a)	No	No	N/A

Notes:

Operator precedence

The following is a table that lists the precedence and associativity of all the operators in the C and C++ languages. Operators are listed top to bottom, in descending precedence. Descending precedence refers to the priority of the grouping of operators and operands. Considering an expression, an operator which is listed on some row will be grouped 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 grouped 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 phrase structure grammar. The table given here has been inferred from the grammar. 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). So, the expression in the middle of the conditional operator (between ? and :) is parsed as if parenthesized. 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 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

Notes

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: 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 x*3); it is equivalent to (++x, x*3).
• Similarly, with 3*x++, 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 3*x). In fact, the expression (tmp=x++, 3*tmp) is evaluated with tmp being a temporary value. It is functionally equivalent to something like (tmp=3*x, ++x, tmp).

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).

Many of the operators containing multi-character sequences are given "names" built from the operator name of each character. 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". 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:

logical-OR-expression ? expression : conditional-expression

while in C++ it is:

logical-OR-expression ? expression : assignment-expression

Hence, the expression:

e = a < d ? a++ : a = d

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:

unary-expression '=' assignment-expression

In C++, it is parsed as:

e = (a < d ? a++ : (a = d))

which is a valid expression.

If you want to use comma-as-operator within a single function argument, variable assignment, or other comma-separated list, you need to use parentheses, e.g.:

int a = 1, b = 2, weirdVariable = (++a, b), d = 4;

Criticism of bitwise and equality operators precedence

The precedence of the bitwise logical operators has been criticized. Conceptually, & and | are arithmetic operators like * and +.

The expression

a & b == 7

is syntactically parsed as

a & (b == 7)

whereas the expression

a + b == 7

is parsed as

(a + b) == 7

. 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

&& ||

didn't exist. Instead

& |

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

if (a==b & c) {...}

it behaved as a logical operator, but in

c = a & b

it behaved as a bitwise one). It was retained so as to keep backward compatibility with existing installations.

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.

C++ operator synonyms

C++ defines certain keywords to act as aliases for a number of operators:

Keyword	Operator
and	&&
and_eq	&=
bitand	&
bitor	|
compl	~
not	!
not_eq	!=
or	||
or_eq	|=
xor	^
xor_eq	^=

These can be used exactly the same way as the punctuation symbols they replace, as they are not the same operator under a different name, but rather simple token replacements for the name (character string) of the respective operator. This means that the expressions (a > 0 and not flag) and (a > 0 && !flag) have identical meanings. It also means that, for example, the bitand keyword may be used to replace not only the bitwise-and operator but also the address-of operator, and it can even be used to specify reference types (e.g., int bitand ref = n). The ISO C specification makes allowance for these keywords as preprocessor macros in the header file iso646.h. For compatibility with C, C++ provides the header ciso646, the inclusion of which has no effect.

See also

• Bitwise operations in C
• Bit manipulation
• Logical operator
• Boolean algebra (logic)
• Table of logic symbols
• Digraphs and trigraphs in C and in C++

External links

• "Operators", C++ reference, https://en.cppreference.com/w/cpp/language/expressions#Operators .
• C Operator Precedence
• Postfix Increment and Decrement Operators: ++ and --, Microsoft, 17 August 2021, https://docs.microsoft.com/en-US/cpp/cpp/postfix-increment-and-decrement-operators-increment-and-decrement .