章 11. Operators

內容目錄
Operator Precedence
Arithmetic Operators
Assignment Operators
Bitwise Operators
Comparison Operators
Error Control Operators
Execution Operators
Incrementing/Decrementing Operators
Logical Operators
String Operators
Array Operators

Operator Precedence

The precedence of an operator specifies how "tightly" it binds two expressions together. For example, in the expression 1 + 5 * 3, the answer is 16 and not 18 because the multiplication ("*") operator has a higher precedence than the addition ("+") operator. Parentheses may be used to force precedence, if necessary. For instance: (1 + 5) * 3 evaluates to 18.

The following table lists the precedence of operators with the lowest-precedence operators listed first.

表格 11-1. Operator Precedence

Associativity Operators
left ,
left or
left xor
left and
right print
left = += -= *= /= .= %= = |= ^= ~= = =
left ? :
left ||
left
left |
left ^
left
non-associative == != === !==
non-associative = =
left
left + - .
left * / %
right ! ~ ++ -- (int) (float) (string) (array) (object) @
right [
non-associative new


注: Although ! has a higher precedence than =, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the output from foo() is put into $a.