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.
When operators have equal precedence their
associativity decides how the operators are grouped. For example "-" is left-associative, so 1 - 2 - 3 is grouped as [1 - 2] - 3 and evaluates to -4. "=" on the other hand is right-associative, so $a = $b = $c is grouped as $a = [$b = $c].
Operators of equal precedence that are non-associative cannot be used next to each other, for example 1 < 2 > 1 is illegal in PHP. The expression 1
Operator precedence and associativity only determine how expressions are grouped, they do not specify an order of evaluation. PHP does not [in the general case] specify in which order an expression is evaluated and code that assumes a specific order of evaluation should be avoided, because the behavior can change between versions of PHP or depending on the surrounding code.
Example #2 Undefined order of evaluation
Example #3 +, - and . have the same precedence [prior to PHP 8.0.0]
The above example will output:
-1, or so I hope -1, or so I hope x minus one equals 3, or so I hope
Note:
Although
=has a lower precedence than most other operators, PHP will still allow expressions similar to the following:if [!$a = foo[]], in which case the return value offoo[]is put into $a.
Changelog
| 8.0.0 | String concatenation [.] now has a lower precedence than arithmetic addition/subtraction [+ and -] and bitwise shift left/right [+ and - and a higher precedence than |
| 8.0.0 | The ternary operator [? :] is non-associative now; previously it was left-associative.
|
| 7.4.0 | Relying on the precedence of string concatenation [.] relative to arithmetic addition/subtraction [+ or -] or bitwise shift left/right [ |
| 7.4.0 | Relying on left-associativity of the ternary operator [? :], i.e. nesting multiple unparenthesized ternary operators, is deprecated.
|
fabmlk ¶
7 years ago
Watch out for the difference of priority between 'and vs &&' or '|| vs or':
karlisd at gmail dot com ¶
6 years ago
Sometimes it's easier to understand things in your own examples.
If you want to play around operator precedence and look which tests will be made, you can play around with this:
Now put in IF arguments f for false and t for true, put in them some ID's. Play out by changing "F" to "T" and vice versa, by keeping your ID the same. See output and you will know which arguments actualy were checked.
tlili dot mokhtar at gmail dot com ¶
1 year ago
An easy trick to get the result of the left shift operation [