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
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.

[add_random_link]

Arithmetic operators[edit]

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

[add_random_link]

Comparison operators/relational
operators[edit]

All comparison operators can be overloaded in
C++.

[add_random_link]

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]

[add_random_link]

Bitwise operators[edit]

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

[add_random_link]

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.

[add_random_link]

Member and pointer operators[edit]

[add_random_link]

Other operators[edit]

Notes:

[add_random_link]

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).

^[7][8][9]

[add_random_link]

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; 

[add_random_link]

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.

[add_random_link]

C++ operator synonyms[edit]

C++ defines^[16] certain keywords to act as aliases for
a number of operators:

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.

[add_random_link]

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++

[add_random_link]

References[edit]

[add_random_link]

External links[edit]

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