precedence - hpgDesigns/hpgdesigns-dev.io GitHub Wiki
In mathematics and programming, the precedence of an operator is the order in which the operator is evaluated in the presence of other operators. For example, in the expression `1 + 4 / 2
- 3 * 4
, division and multiplication have the highest precedence. Hence, they are performed first, from left to right, leaving1 + 2 - 12`, the sum of which is simply 15.
Using the more complicated set of operators available in C++ (and, by extension, in EDL), the following table (shamelessly stolen from cppreference.com) lists operators in the order they are evaluated:
| Precedence | Operator | Description | Associativity |
|---|---|---|---|
| 1 | :: |
Scope resolution | Left-to-right |
| 2 |
++ --
|
Suffix/postfix increment and decrement | |
() |
Function call | ||
[] |
Array subscripting | ||
. |
Element selection by reference | ||
−> |
Element selection through pointer | ||
| 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 | ||
delete, delete[]
|
Dynamic memory deallocation | ||
| 4 |
.* ->*
|
Pointer to member | Left-to-right |
| 5 |
* / %
|
Multiplication, division, and remainder | |
| 6 |
+ −
|
Addition and subtraction | |
| 7 |
<< >>
|
Bitwise left shift and right shift | |
| 8 |
< <=
|
For relational operators < and ≤ respectively | |
> >=
|
For relational operators > and ≥ respectively | ||
| 9 |
== !=
|
For relational = and ≠ respectively | |
| 10 | & |
Bitwise AND | |
| 11 | ^ |
Bitwise XOR (exclusive or) | |
| 12 | | |
Bitwise OR (inclusive or) | |
| 13 | && |
Logical AND | |
| 14 | |
Logical OR | |
| 15 | ?: |
Ternary conditional | Right-to-Left |
| 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 (for exceptions) | |
| 18 | , |
Comma | Left-to-right |
Hence, 1 == 2 << 3 + 4 * 5 is actually performed right to left, since
the operators are of ascending precedence. Multiplication is performed
first, then addition, then the left shift, then the comparison. Writing
it as 5 * 4 + 3 << 2 == 1 does not change the order in which they are
performed, but does change the result, as a << b is not
the same as b << a. This is known as communativity.