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An expression is a sequence of operators and their operands, that specifies a computation.

Expression evaluation may produce a result (e.g., evaluation of 2+2 produces the result 4) and may generate side-effects (e.g. evaluation of std::printf("%d",4) prints the character '4' on the standard output).

Contents

General

  • value categories (lvalue, rvalue, glvalue, prvalue, xvalue) classify expressions by their values
  • order of evaluation of arguments and subexpressions specify the order in which intermediate results are obtained

Operators

Common operators
assignment increment
decrement
arithmetic logical comparison member
access
other

a = b
a = rvalue
a += b
a -= b
a *= b
a /= b
a %= b
a &= b
a |= b
a ^= b
a <<= b
a >>= b

++a
--a
a++
a--

+a
-a
a + b
a - b
a * b
a / b
a % b
~a
a & b
a | b
a ^ b
a << b
a >> b

!a
a && b
a || b

a == b
a != b
a < b
a > b
a <= b
a >= b

a[b]
*a
&a
a->b
a.b
a->*b
a.*b

a(...)
a, b
(type) a
? :

Special operators

static_cast converts one type to another compatible type
dynamic_cast converts virtual base class to derived class
const_cast converts type to compatible type with different cv qualifiers
reinterpret_cast converts type to incompatible type
new allocates memory
delete deallocates memory
sizeof queries the size of a type
sizeof... queries the size of a parameter pack (since C++11)
typeid queries the type information of a type
noexcept checks if an expression can throw an exception (since C++11)
alignof queries alignment requirements of a type (since C++11)

Conversions

Memory allocation

Other


Primary expressions

The operands of any operator may be other expressions or primary expressions (e.g. in 1+2*3, the operands of operator+ are the subexpression 2*3 and the primary expression 1).

Primary expressions are any of the following:

1) Literals (e.g. 2 or "Hello, world")
2) Suitably declared unqualified identifiers (e.g. n or cout)
3) Suitably declared qualified identifiers (e.g. std::string::npos)

Any expression in parentheses is also classified as a primary expression: this guarantees that the parentheses have higher precedence than any operator.

Literals

Literals are the tokens of a C++ program that represent constant values embedded in the source code.

Unevaluated expressions

The operands of the four operators typeid, sizeof, noexcept, and decltype are expressions that are not evaluated, since these operators only query the compile-time properties of their operands. Thus, std::size_t n = sizeof(std::cout << 42); does not perform console output.