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', indicates whether an operator is also present in C. Note that C does not support operator overloading.

When not overloaded, for the operators &&, ||, ?: (the Ternary operator), 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 Java, Perl, C#, 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
Unary plus		+a	Yes	Yes	T T::operator +() const;	T operator +(const T& a);
Addition		a + b	Yes	Yes	T T::operator +(const T& b) const;	T operator +(const T& a, const T& b);
Increment	Prefix	++a	Yes	Yes	T& T::operator ++();	T& operator ++(T& a);
	Postfix	a++	Yes	Yes	T T::operator ++(int);	T operator ++(T& a, int);
					Note: C++ uses the unnamed dummy-parameter int to differentiate between prefix and postfix increment operators.
Assignment by addition		a += b	Yes	Yes	T& T::operator +=(const T& b);	T& operator +=(T& a, const T& b);
Unary minus (negation)		-a	Yes	Yes	T T::operator -() const;	T operator -(const T& a);
Subtraction (difference)		a - b	Yes	Yes	T T::operator -(const T& b) const;	T operator -(const T& a, const T& b);
Decrement	Prefix	--a	Yes	Yes	T& T::operator --();	T& operator --(T& a);
	Postfix	a--	Yes	Yes	T T::operator --(int);	T operator --(T& a, int);
					Note: C++ uses the unnamed dummy-parameter int to differentiate between prefix and postfix decrement operators.
Assignment by subtraction		a -= b	Yes	Yes	T& T::operator -=(const T& b);	T& operator -=(T& a, const T& b);
Multiplication (product)		a * b	Yes	Yes	T T::operator *(const T& b) const;	T operator *(const T &a, const T& b);
Assignment by multiplication		a *= b	Yes	Yes	T& T::operator *=(const T& b);	T& operator *=(T& a, const T& b);
Division (quotient)		a / b	Yes	Yes	T T::operator /(const T& b) const;	T operator /(const T& a, const T& b);
Assignment of division		a /= b	Yes	Yes	T& T::operator /=(const T& b);	T& operator /=(T& a, const T& b);
Modulo (remainder)		a % b	Yes	Yes	T T::operator %(const T& b) const;	T operator %(const T& a, const T& b);
Assignment of modulo		a %= b	Yes	Yes	T& T::operator %=(const T& b);	T& operator %=(T& a, const T& b);

Comparison operators/Relational operators

Operator name		Syntax	Overloadable	Included in C	Prototype examples (T is any type)
					As member of T	Outside class definitions
Less than		a < b	Yes	Yes	bool T::operator <(const T& b) const;	bool operator <(const T& a, const T& b);
Less than or equal to		a <= b	Yes	Yes	bool T::operator <=(const T& b) const;	bool operator <=(const T& a, const T& b);
Greater than		a > b	Yes	Yes	bool T::operator >(const T& b) const;	bool operator >(const T& a, const T& b);
Greater than or equal to		a >= b	Yes	Yes	bool T::operator >=(const T& b) const;	bool operator >=(const T& a, const T& b);
Not equal to		a != b	Yes	Yes	bool T::operator !=(const T& b) const;	bool operator !=(const T& a, const T& b);
Equal to		a == 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)		!a	Yes	Yes	bool T::operator !() const;	bool operator !(const T& a);
Logical AND		a && b	Yes	Yes	bool T::operator &&(const T& b) const;	bool operator &&(const T& a, const T& b);
Logical OR		a || 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 (T1 and T2 are types)
					As member of T1	Outside class definitions
Bitwise left shift		a << b	Yes	Yes	T1 T1::operator <<(const T2& b) const;	T1 operator <<(const T1& a, const T2& b);
Assignment by bitwise left shift		a <<= b	Yes	Yes	T1& T1::operator <<=(const T2& b);	T1& operator <<=(T1& a, const T2& b);
Bitwise right shift		a >> b	Yes	Yes	T1 T1::operator >>(const T2& b) const;	T1 operator >>(const T1& a, const T2& b);
Assignment by bitwise right shift		a >>= b	Yes	Yes	T1& T1::operator >>=(const T2& b);	T1& operator >>=(T1& a, const T2& b);
Bitwise ones′ complement (NOT)		~a	Yes	Yes	T1 T1::operator ~() const;	T1 operator ~(const T1& a);
Bitwise AND		a & b	Yes	Yes	T1 T1::operator &(const T2& b) const;	T1 operator &(const T1& a, const T2& b);
Assignment by bitwise AND		a &= b	Yes	Yes	T1& T1::operator &=(const T2& b);	T1& operator &=(T1& a, const T2& b);
Bitwise OR		a | b	Yes	Yes	T1 T1::operator |(const T2& b) const;	T1 operator |(const T1& a, const T2& b);
Assignment by bitwise OR		a |= b	Yes	Yes	T1& T1::operator |=(const T2& b);	T1& operator |=(T1& a, const T2& b);
Bitwise XOR		a ^ b	Yes	Yes	T1 T1::operator ^(const T2& b) const;	T1 operator ^(const T1& a, const T2& b);
Assignment by bitwise XOR		a ^= b	Yes	Yes	T1& T1::operator ^=(const T2& b);	T1& operator ^=(T1& a, const T2& b);

Other operators

Operator name		Syntax	Overloadable	Included in C	Prototype examples
					As member of T1	Outside class definitions
Basic assignment		a = b	Yes	Yes	R T1::operator =(T2);	—
Function call See Function object.		a()	Yes	Yes	R T1::operator ()(T2, T3, …);	—
Array subscript		a[b]	Yes	Yes	R T1::operator [](T2);	—
Indirection (dereference)		*a	Yes	Yes	R T1::operator *();	R operator *(T1);
Address-of (reference)		&a	Yes	Yes	T1* T1::operator &();	T1* operator &(T1& a);
Member by pointer		a->b	Yes	Yes	T2* T1::operator ->();	—
Member		a.b	No	Yes	—
Bind pointer to member by pointer		a->*b	Yes	No	R T1::operator->*(T2);	R operator->*(T1, T2);
Bind pointer to member by reference		a.*b	No	No	—
cast		(type) a	Yes	Yes	T1::operator T2() const;	—
					Note: for user-defined conversions, the return type implicitly and necessarily matches the operator name.
comma		a, b	Yes	Yes	T2& T1::operator ,(T2& b) const;	T2& operator ,(const T1& a, T2& b);
ternary conditional		a ? b : c	No	Yes	—
Scope resolution		a::b	No	No	—
size-of		sizeof(a) sizeof(T1)	No	Yes	—
Type identification		typeid(a) typeid(type)	No	No	—
Allocate storage		new type	Yes	No	void* T1::operator new(size_t x);	void* operator new(size_t x);
Allocate storage (array)		new type[n]	Yes	No	void* T1::operator new[](size_t x);	void* operator new[](size_t x);
Deallocate storage		delete a	Yes	No	void T1::operator delete(void* x);	void operator delete(void* x);
Deallocate storage (array)		delete[] a	Yes	No	void T1::operator delete[](void* x);	void operator delete[](void* x);

Notes:

Operator precedence

The following is a table that lists the precedence and associativity of all the operators in the C++ and C programming 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. 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). 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	++ --	Postfix increment and decrement
	()	Function call
	[]	Array subscripting
	.	Element selection by reference
	->	Element selection through pointer
	typeid()	Run-time type information (C++ only)
	const_cast	Type cast (C++ only)
	dynamic_cast	Type cast (C++ only)
	reinterpret_cast	Type cast (C++ only)
	static_cast	Type cast (C++ only)
3	++ --	Prefix increment and decrement	Right-to-left
	+ -	Unary plus and minus
	! ~	Logical NOT and bitwise NOT
	(type)	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	c ? t : f	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, ++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); it is functionally equivalent to something like (tmp=3*x, x++, tmp) with tmp being a temporary value.

Precedence and bindings

• 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 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, but many compilers parse it as:

e = ((a < d ? a++ : a) = d)

which is a semantic error, since the result of the conditional-expression (which might be a++) is not an lvalue. In C++, it is parsed as:

e = (a < d ? a++ : (a = d))

which is a valid expression.

The precedence of the bitwise logical operators has been criticized.[1] 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.

C++ operator synonyms

C++ defines keywords to act as aliases for a number of symbols that function as operators: and (&&), bitand (&), and_eq (&=), or (||), bitor (|), or_eq (|=), xor (^), xor_eq (^=), not (!), not_eq (!=), compl (~). These are parsed exactly like their symbolic equivalents, and can be used in place of the symbol they replace. It is the character or string that is aliased, not the operator. As a result, bitand (e.g.) is used to replace both the bitwise AND operator and the address-of operator.

The ANSI 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; inclusion of which has no effect.

External links

• Basic types & Operators
• Prefix vs. postfix operators in C and C++