Operators in C and C++

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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 &&, ||, ?:, 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.

Contents

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 example

(T1 and T2 are types)

Unary plus +a Yes Yes T1 operator +(const T1& a);
Addition (sum) a + b Yes Yes T1 operator+(const T1& a, const T1& b);
Prefix increment ++a Yes Yes T1& operator++ (T1& a);
Postfix increment a++ Yes Yes T1 operator++ (T1& a, int);

(The int argument is required by C++ to differentiate the operator from a prefix-increment operator.)

Assignment by addition a += b Yes Yes T1& operator+=(T1& a, const T1& b);
Unary minus (negation) -a Yes Yes T1 operator-(const T1& a);
Subtraction (difference) a - b Yes Yes T1 operator-(const T1& a, const T1& b);
Prefix decrement --a Yes Yes T1& operator--(T1& a);
Postfix decrement a-- Yes Yes T1 operator--(T1& a, int);
Assignment by subtraction a -= b Yes Yes T1& operator-=(T1& a, const T1& b);
Multiplication (product) a * b Yes Yes T1 operator*(const T1 &a, const T1& b);
Assignment by multiplication a *= b Yes Yes T1& operator*=(T1& a, const T1& b);
Division (quotient) a / b Yes Yes T1 operator/(const T1& a, const T1& b);
Assignment of division a /= b Yes Yes T1& operator/=(T1& a, const T1& b);
Modulo (remainder) a % b Yes Yes T1 operator%(const T1& a, const T1& b);
Assignment of modulo a %= b Yes Yes T1& operator%=(T1& a, const T1& b);

Comparison operators/Relational operators

Operator name Syntax Overloadable Included in C Prototype example
Less than a < b Yes Yes bool operator<(const T1& a, const T2& b);

bool T1::operator<(const T2& b) const;

Less than or equal to a <= b Yes Yes bool operator<=(const T1& a, const T2& b);
Greater than a > b Yes Yes bool operator>(const T1& a, const T2& b);
Greater than or equal to a >= b Yes Yes bool operator>=(const T1& a, const T2& b);
Not equal to a != b Yes Yes bool operator!=(const T1& a, const T2& b);
Equal to a == b Yes Yes bool operator==(const T1& a, const T2& b);

Logical operators

Operator name Syntax Overloadable Included in C Prototype example
Logical negation (NOT) !a Yes Yes bool operator!(const T1& a);
Logical AND a && b Yes Yes bool operator&&(const T1& a, const T2& b);
Logical OR a || b Yes Yes bool operator||(const T1& a, const T2& b);

Bitwise operators

Operator name Syntax Overloadable Included in C Prototype example
Bitwise left shift a << b Yes Yes T1 operator<<(const T1& a, const T2& b);
Assignment by bitwise left shift a <<= b Yes Yes T1& operator<<=(T1& a, const T2& b);
Bitwise right shift a >> b Yes Yes T1 operator>>(const T1& a, const T2& b);
Assignment by bitwise right shift a >>= b Yes Yes T1& operator>>=(T1& a, const T2& b);
Bitwise one's complement (NOT) ~a Yes Yes T1 operator~(const T1& a);
Bitwise AND a & b Yes Yes T1 operator&(const T1& a, const T2& b);
Assignment by bitwise AND a &= b Yes Yes T1& operator&=(T1& a, const T2& b);
Bitwise OR a | b Yes Yes T1 operator|(const T1& a, const T2& b);
Assignment by bitwise OR a |= b Yes Yes T1& operator|=(T1& a, const T2& b);
Bitwise XOR a ^ b Yes Yes T1 operator^(const T1& a, const T2& b);
Assignment by bitwise XOR a ^= b Yes Yes T1& operator^=(T1& a, const T2& b);

Other operators

Operator name Syntax Overloadable Included in C Prototype example
Basic assignment a = b Yes Yes T1& T1::operator= (const T2& b);
Function call a() Yes Yes void operator() (T1& a);
Array subscript a[b] Yes Yes const T2& operator[] (const T1& a, const T2& b);
Indirection (dereference) *a Yes Yes T2& operator* (T1& a);
Address-of (reference) &a Yes Yes T2* operator& (T1& a);
Member by pointer a->b Yes Yes T2* T1::operator-> (); // must be a member function
Member a.b No Yes N/A
Bind pointer to member by pointer a->*b Yes No N/A
Bind pointer to member by reference a.*b No No N/A
cast (type) a Yes Yes T1::operator type(); // must be a member function and return an object of type type
comma a , b Yes Yes T2& operator, (const T1& a, T2& b);
ternary conditional a ? b : c No Yes N/A
Scope resolution a::b No No N/A
Pointer to member a::*b No No N/A
size-of sizeof a
sizeof(type)
No Yes N/A
Type identification typeid(a)
typeid(type)
No No N/A
Allocate storage new type Yes No void *T1::operator new(size_t x)
Allocate storage (array) new type[n] Yes No void *T1::operator new[](size_t x)
Deallocate storage delete a Yes No void T1::operator delete(void *x)
Deallocate storage (array) delete[] a Yes No void T1::operator delete[](void *x)

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.[citation needed] The table given here has been inferred from the grammar.[citation needed]

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 < <= Relational “less than” and “less than or equal to”
> >= Relational “greater than” and “greater than or equal to”
9 == != Relational “equal to” and “not equal to”
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
(Not available for throw)
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.
File:Precedence 2.png
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 parsed 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[1] 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 punctuation that is aliased, not the operators. For example, bitand can 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.

All comparison operators (see tables at top) return a bool.

    bool a;
    int b = 1;
    int c = 2;
    a = b == c;

That will work since == returns a boolean, never requiring it to be inside of an if statement or something similar. a = b == c; is also shorthand for

    bool a;
    int b = <Some Number Here>;
    int c = <Some Number Here>;
    if(b == c)
        a = true;
    else
        a = false;

External links

References

  1. ISO/IEC JTC1/SC22/WG21 - The C++ Standards Committee (1 September 1998). ISO/IEC 14882:1998(E) Programming Language C++. International standardization working group for the programming language C++. pp. 40–41. 
es:Operadores de C y C++

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