An operator is a C symbol or symbol sequence that specifies an operation on one or more operands. In a + b, + is the operator, while a and b are operands. section 4.1
Binding and arithmetic
With size_t a = 45 and size_t b = 7, (a - b) * 2 produces 76, whereas a - b * 2 produces 31. Parentheses group sub-expressions and enforce the intended binding. Unary + provides a value and unary - produces its negative. section 4.2.1
C organizes operators by what they operate on:
- Value operators perform arithmetic, bit, comparison, and related operations. section 4.1
- Object operators evaluate, assign, increment, access members, subscript arrays, obtain addresses, and determine size or alignment. section 4.1
- Type operators such as sizeof, alignof, and offsetof produce integer constants describing size, alignment, or member offset. section 4.1
Operator meaning depends on operand types. Binary expressions such as a*b+c can work across wide integer, floating, complex, and pointer types; conversions reconcile operands when required, while some operators accept differing types directly. section 18.1.1
For size_t, +, -, and * produce the mathematically correct result when representable; unsigned arithmetic remains well defined, but an unrepresentable result is arithmetic overflow. section 4.2.1
Operators also participate in sequencing. An operator runs after its operands are evaluated, and assignment, increment, or decrement updates occur after operand evaluation; side effects can still produce indeterminate results in larger expressions. section 19.2
Table 4.1 Value operators: The Form column gives the syntactic form of the operation, where @ represents the operator and a and possibly b denote values that serve as operands. For arithmetic and bit operations, the type of the result is a type that reconciles the types of a and b. For some of the operators, the Nick column gives an alternative form of the operator or lists a combination of operators that has special meaning. Most of the operators and terms will be discussed later.
| Type restriction | ||||||
| Operator | Nick | Form | a |
b |
Result | |
a |
Narrow | Wide | Promotion | |||
+ - |
a@b |
Pointer | Integer | Pointer | Arithmetic | |
+ - * / |
a@b |
Arithmetic | Arithmetic | Arithmetic | Arithmetic | |
+ - |
@a |
Arithmetic | Arithmetic | Arithmetic | ||
% |
a@b |
Integer | Integer | Integer | Arithmetic | |
|
compl |
@a |
Integer | Integer | Bit | |
& |
bitand |
a@b |
Integer | Integer | Integer | Bit |
| |
bitor |
|||||
^ |
xor |
|||||
<< >> |
a@b |
Integer | Positive | Integer | Bit | |
== < > <= >= |
a@b |
Scalar | Scalar | 0,1 |
Comparison | |
!= |
not_eq |
a@b |
Scalar | Scalar | 0,1 |
Comparison |
!!a |
a |
Scalar | 0,1 |
Logic | ||
!a |
not |
@a |
Scalar | 0,1 |
Logic | |
&& || |
and or |
a@b |
Scalar | Scalar | 0,1 |
Logic |
. |
a@m |
struct |
Value | Member | ||
* |
@a |
Pointer | Object | Reference | ||
[] |
a[b] |
Pointer | Integer | Object | Member | |
-> |
a@m |
struct pointer |
Object | Member | ||
() |
a(b ...) |
Function pointer | Value | Call | ||
sizeof |
@ a |
None | size_t |
Size, ICE | ||
alignof |
_Alignof |
@(a) |
None | size_t |
Alignment, ICE |
Use the value-operator table as a compact reference for forms, operand restrictions, promotions, and result types. section 4.1
