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Wednesday Feb 08, 2023

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
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[edit]

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.

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Arithmetic operators[edit]

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 RK::operator+(Sb); Roperator+(Ka,Sb);
Subtraction a - b RK::operator-(Sb); Roperator-(Ka,Sb);
Unary plus (integer promotion) +a RK::operator+(); Roperator+(Ka);
Unary minus (additive inverse) -a RK::operator-(); Roperator-(Ka);
Multiplication a * b RK::operator*(Sb); Roperator*(Ka,Sb);
Division a / b RK::operator/(Sb); Roperator/(Ka,Sb);
Modulo (integer remainder)[a] a % b RK::operator%(Sb); Roperator%(Ka,Sb);
Increment Prefix ++a R&K::operator++(); R&operator++(K&a);
Postfix a++ RK::operator++(int); Roperator++(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-- RK::operator--(int); Roperator--(K&a,int);
Note: C++ uses the unnamed
dummy-parameter int to differentiate between prefix and postfix
decrement operators.

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Comparison operators/relational
operators[edit]

All comparison operators can be overloaded in
C++.

Operator name Syntax Includedin C Prototype examples
As member of K Outside class definitions
Equal to a == b Yes boolK::operator==(Sconst&b)const; booloperator==(Kconst&a,Sconst&b);
Not equal to a != ba not_eq b[b] Yes boolK::operator!=(Sconst&b)const; booloperator!=(Kconst&a,Sconst&b);
Greater than a > b Yes boolK::operator>(Sconst&b)const; booloperator>(Kconst&a,Sconst&b);
Less than a < b Yes boolK::operator<(Sconst&b)const; booloperator<(Kconst&a,Sconst&b);
Greater than or equal to a >= b Yes boolK::operator>=(Sconst&b)const; booloperator>=(Kconst&a,Sconst&b);
Less than or equal to a <= b Yes boolK::operator<=(Sconst&b)const; booloperator<=(Kconst&a,Sconst&b);
Three-way
comparison[c]
a <=>
b
No autoK::operator<=>(constS&b); autooperator<=>(constK&a,constS&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.

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Logical operators[edit]

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.[1]

Operator name Syntax C++ prototype examples
As member of K Outside class definitions
Logical negation
(NOT)
!anot
a
[b]
boolK::operator!(); booloperator!(Ka);
Logical AND a && b a and b[b] boolK::operator&&(Sb); booloperator&&(Ka,Sb);
Logical OR a || ba ??!??! b[d][e]a or b[b] boolK::operator||(Sb); booloperator||(Ka,Sb);

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Bitwise operators[edit]

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[d]compl a[b] RK::operator~(); Roperator~(Ka);
Bitwise AND a & b a bitand b[b] RK::operator&(Sb); Roperator&(Ka,Sb);
Bitwise OR a | ba ??! b[d]a bitor
b
[b]
RK::operator|(Sb); Roperator|(Ka,Sb);
Bitwise XOR a ^ ba ??' b[d]a xor b[b] RK::operator^(Sb); Roperator^(Ka,Sb);
Bitwise left shift[f] a << b RK::operator<<(Sb); Roperator<<(Ka,Sb);
Bitwise right shift[f][g] a >> b RK::operator>>(Sb); Roperator>>(Ka,Sb);

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Assignment operators[edit]

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=(Sb);
Addition assignment a += b R&K::operator+=(Sb); R&operator+=(K&a,Sb);
Subtraction assignment a -= b R&K::operator-=(Sb); R&operator-=(K&a,Sb);
Multiplication assignment a *= b R&K::operator*=(Sb); R&operator*=(K&a,Sb);
Division assignment a /= b R&K::operator/=(Sb); R&operator/=(K&a,Sb);
Modulo assignment a %= b R&K::operator%=(Sb); R&operator%=(K&a,Sb);
Bitwise AND assignment a &= ba and_eq b[b] R&K::operator&=(Sb); R&operator&=(K&a,Sb);
Bitwise OR assignment a |= ba ??!= b[d]a or_eq
b
[b]
R&K::operator|=(Sb); R&operator|=(K&a,Sb);
Bitwise XOR assignment a ^= ba ??'= b[d]a xor_eq
b
[b]
R&K::operator^=(Sb); R&operator^=(K&a,Sb);
Bitwise left shift assignment a <<= b R&K::operator<<=(Sb); R&operator<<=(K&a,Sb);
Bitwise right shift assignment[g] a >>= b R&K::operator>>=(Sb); R&operator>>=(K&a,Sb);

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Member and pointer operators[edit]

Operator name Syntax Can overload in C++ Includedin C C++ prototype examples
As member of K Outside class definitions
Subscript a[b]a<:b:>a??(b??)[d][h] Yes Yes R&K::operator[](Sb);
Indirection (“object pointed to by
a“)
*a Yes Yes R&K::operator*(); R&operator*(Ka);
Address-of (“address of
a“)
&abitand a[b][i] Yes Yes R*K::operator&(); R*operator&(Ka);
Structure dereference (“member
b of object pointed to by a“)
a->b Yes Yes R*K::operator->();[j]
Structure reference (“member b
of object a“)
a.b No Yes
Member selected by pointer-to-member
b of object pointed to by a[k]
a->*b Yes No R&K::operator->*(Sb); R&operator->*(Ka,Sb);
Member of object a selected by
pointer-to-member b
a.*b No No

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Other operators[edit]

Operator name Syntax Can overload in C++ Includedin C Prototype examples
As member of K Outside class definitions
Function
callSee Function object.
a(a1, a2) Yes Yes RK::operator()(Sa,Tb,...);
Comma a, b Yes Yes RK::operator,(Sb); Roperator,(Ka,Sb);
Ternary conditional a ? b :
c
No Yes
Scope resolution a::b No No
User-defined literals[l]since
C++11
"a"_b Yes No Roperator""_b(Ta)
Sizeof sizeof a[m]sizeof (type) No Yes
Size of parameter packsince
C++11
sizeof...(Args) No No
Alignofsince C++11 alignof(type) or
_Alignof(type)[n]
No Yes
Type identification typeid(a)typeid(type) No No
Conversion (C-style cast) (type)a Yes Yes K::operatorR();[3]
Conversion type(a) No No Note: behaves like
const_cast/static_cast/reinterpret_cast[4]
static_cast
conversion
static_cast<type>(a) Yes No K::operatorR();explicitK::operatorR(); since C++11
Note: for user-defined conversions,
the return type implicitly and necessarily matches the operator
name.
dynamic cast conversion dynamic_cast<type>(a) No No
const_cast conversion const_cast<type>(a) No No
reinterpret_cast conversion reinterpret_cast<type>(a) No No
Allocate storage new type Yes No void*K::operatornew(size_tx); void*operatornew(size_tx);
Allocate storage (array) new type[n]new type<:n:>new
type??(n??)
[d][h]
Yes No void*K::operatornew[](size_ta); void*operatornew[](size_ta);
Deallocate storage delete a Yes No voidK::operatordelete(void*a); voidoperatordelete(void*a);
Deallocate storage (array) delete[] adelete<::> adelete??(??) a[d][h] Yes No voidK::operatordelete[](void*a); voidoperatordelete[](void*a);
Exception checksince
C++11
noexcept(a) No No

Notes:

  1. ^ The modulus
    operator works just with integer operands, for floating point
    numbers a library function must be used instead (like fmod).
  2. ^ a b
    c d e
    f g h
    i j k
    l Requires
    iso646.h in C. See C++ operator synonyms
  3. ^
    About C++20 three-way comparison
  4. ^ a b
    c d e
    f g h
    i Trigraphs were removed in
    C++17. They are still available in C as of C17 but will be removed
    in C23.
  5. ^ Since
    trigraphs are simply substituted by the preprocessor, the different
    representations of the characters in this operator can be mixed and
    matched in any way. For brevity, only the forms that use only
    trigraphs and neither are provided.
  6. ^ 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.
  7. ^ a b
    According to the C99 standard, the right shift of a negative number
    is implementation defined. Most implementations, e.g., the
    GCC,[2] use an
    arithmetic shift (i.e., sign extension), but a logical shift is
    possible.
  8. ^ a b
    c The brackets do not need
    to match as the trigraph bracket is substituted by the preprocessor
    and the digraph bracket is an alternative token that is equivalent.
    Only the cases where the brackets match are included since the
    other forms can be easily derived from the provided ones.
  9. ^ This
    alternative form is a side effect of the bitwise and alternative
    form for reasons explained in C++ operator synonyms
  10. ^ The return
    type of operator->() must be a type for which the
    -> operation can be
    applied, such as a pointer type. If x is of type C where C overloads operator->(), x->y gets expanded to x.operator->()->y.
  11. ^Meyers, Scott (October 1999),
    “Implementing operator->* for Smart Pointers” (PDF), Dr.
    Dobb’s Journal
    , Aristeia
    .
  12. ^ About C++11
    User-defined literals
  13. ^ 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.
  14. ^ C++ defines
    alignof operator, whereas C defines
    _Alignof. Both operators have the same semantics.

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Operator precedence[edit]

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.[5] 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.”[6]

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

[7][8][9]

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Notes[edit]

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.[10][11]

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,[12][13] e.g.:

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

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Criticism of bitwise and equality operators
precedence[edit]

The precedence of the bitwise logical operators
has been criticized.[14] 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.[15]

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.

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C++ operator synonyms[edit]

C++ defines[16] 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.

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See also[edit]

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

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References[edit]

  1. ^ “Standard C++”.
  2. ^ “Integers implementation”, GCC 4.3.3,
    GNU
    .
  3. ^ “user-defined conversion”. Retrieved 5 April
    2020.
  4. ^ Explicit type
    conversion in C++
  5. ^ ISO/IEC 9899:201x Programming Languages –
    C
    . open-std.org – The C Standards Committee. 19 December 2011.
    p. 465.
  6. ^ the ISO C 1999 standard, section 6.5.6
    note 71
    (Technical report). ISO. 1999.
  7. ^ “C Operator Precedence – cppreference.com”.
    en.cppreference.com. Retrieved 16 July 2019.
  8. ^ “C++ Built-in Operators, Precedence and
    Associativity”. docs.microsoft.com. Retrieved 11 May
    2020.
  9. ^ “C++ Operator Precedence – cppreference.com”.
    en.cppreference.com. Retrieved 16 July 2019.
  10. ^ “C Operator Precedence – cppreference.com”.
    en.cppreference.com. Retrieved 10 April 2020.
  11. ^ “Does the C/C++ ternary operator actually have
    the same precedence as assignment operators?”. Stack
    Overflow
    . Retrieved 22 September 2019.
  12. ^ “Other operators – cppreference.com”.
    en.cppreference.com. Retrieved 10 April 2020.
  13. ^ “c++ – How does the Comma Operator work”.
    Stack Overflow. Retrieved 1 April 2020.
  14. ^ C history § Neonatal C, Bell
    labs
    .
  15. ^ “Re^10: next unless condition”.
    www.perlmonks.org. Retrieved 23 March 2018.
  16. ^ ISO/IEC 14882:1998(E) Programming Language
    C++
    . open-std.org – The C++ Standards Committee. 1 September
    1998. pp. 40–41.

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External links[edit]

  • “Operators”, C++ reference
    (wiki)
    .
  • C Operator Precedence
  • Postfix Increment and Decrement Operators: ++ and
    (Developer network), Microsoft
    .

Retrieved from
“https://en.wikipedia.org/w/index.php?title=Operators_in_C_and_C%2B%2B&oldid=1131194495”

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