PHP operators

Arithmetic operator
Assignment operator
An operator
Comparison operator
Error control operators
The execution operator
Increasing （ reduce ） Operator
Logical operators
String operators
Array operators
Type operators
Operator priority

Arithmetic operator

Common arithmetic operators include

-$a, Take the opposite
$a + $b, Add ,a and a and b And
$a - $b, Subtraction ,a and a and b Difference
$a * $b, Multiplication ,a and a and b Product of
$a / $b, division ,a and a and b The business of
$a % $b, Remainder ,a Divide a Divide b The remainder of
$a ** $b, chengfang ,a Of a Of b Power
edit /home/project/arithmetic.php

<?php

$a = 9 / 3;
$b = 9 / 4;
$c = -5 % 3;
$d = 5 % -3;
$e = 2 ** -2;

echo <<<EOT 9 / 3 = $a 9 / 4 = $b -5 % 3 = $c 5 % -3 = $d 2 ** -2 = $e EOT;

perform

php arithmetic.php

It can be seen from the results

• The division operator always returns a floating point number . Only in the following cases ： Both operands are integers （ Or an integer converted from a string ） And it can just divide , Then it returns an integer .
• The operands of the remainder operator are converted to integers before operation （ Remove the decimal part ）. And the sign of the result and the divisor （ The sign ） identical . namely a %ab The result and $a The same symbol as .

Assignment operator

The basic assignment operator is =, It means assigning the value of the expression on the right to the operand on the left .

The value of the assignment expression is the assigned value . in other words ,$a = 3 The value of is 3. So you can do some tricks ：

<?php

$a = ($b = 4) + 5; // $a  Now it's  9, and  $b  a  4.

For arrays array, Assigning values to named keys is done with => Operator . This operator has the same priority as other assignment operators .

<?php

$a = ['a' => 1, 'b' => 3 * 4];

Outside the basic assignment operator , And for all binary arithmetic , Combination operator of array set and string operator , You can assign it a value to the result of such an expression , for example ：

<?php

$a = 3;
$a += 5; // amount to  $a = $a + 5;
$b = "Hello ";
$b .= "There!"; // amount to  $b = $b. "There" ;

Note that the assignment operation copies the value of the original variable into the new variable （ Pass value assignment ）, So changing one doesn't affect the other . This is also suitable for copying some values in a dense loop, such as a large array .

Reference assignment

PHP Support reference assignment , Reference assignment means that two variables point to the same data , Didn't copy anything .

edit /home/project/assign.php

<?php

$arr1 = $arr2 = [1,2,3];

foreach($arr1 as &$a) {
    
    $a++;
}
foreach($arr2 as $a) {
    
    $a++;
}
print_r($arr1);
print_r($arr2);

perform

php assign.php
As can be seen from the results , Reference assignment will change the original value , Value assignment will not .

Comparison operator

Comparison operator , As their name implies , Allows two values to be compared .

• $a == $b, If after type conversion a be equal to a be equal to b, return TRUE.
• $a === $b, If a be equal to a be equal to b, And they're of the same type , return TRUE.
• $a != $b, If after type conversion a It's not equal to a It's not equal to b, return TRUE.
• $a <> $b, Equate to !=
• $a !== $b, If a and a and b Different values or types , return TRUE.
• $a < $b , If a Strictly less than a Strictly less than b, return TRUE.
• $a > $b, If a Strictly greater than a Strictly greater than b, return TRUE.
• $a <= $b, If a Less than or equal to a Less than or equal to b, return TRUE.
• $a >= $b, If a Greater than or equal to a Greater than or equal to b, return TRUE.
  If you compare a number to a string or a string that involves the contents of a number , The string will be converted to a numeric value and the comparison will be performed according to the numeric value . This rule also applies to switch sentence . When used === or !== When comparing, there is no type conversion , Because at this time, the type and value must be compared .

edit /home/project/compare.php

<?php

var_dump(null == "");
var_dump(null == false);
var_dump(true > false);
var_dump(0 == "a");
var_dump("1" == "01");
var_dump("10" == "1e1");
var_dump(100 == "1e2");
var_dump([4,5] < [1,2,3]);
var_dump((object)"Test" > "Test");
var_dump((object)"Test" > [2,3]);

switch ("a") {
    
case 0:
    echo "0";
    break;
case "a":
    echo "a";
    break;
}

perform

php compare.php

It can be seen from the results

• null or String and string When comparing , take null Convert to “”, Compare numbers or words
• bool or null When compared with other types , Convert to bool,FALSE < TRUE
• string,resource or number When comparing with each other , Convert a string or resource to a number , Compare... By ordinary numbers
• array When comparing between , Arrays with fewer members are smaller
• object When compared with other types ,object Always bigger
• array When compared with other types ,array Always bigger , But smaller than the object
• switch When the first condition is satisfied , The following statements that meet the conditions will not be executed

Increasing （ reduce ） Operator

Common incremental （ reduce ） Operator

• ++$a,a Add one to return a Add one to return a.
• $a++, return a, And then a, And then a Add one to the value of .
• --$a,a Minus one returns a Minus one returns a.
• $a--, return a, And then a, And then a Value of minus one .
  Increasing （ reduce ） Operator on Boolean and NULL Impact of type

<?php

$a = null;
$b = true;

var_dump(++$a, --$a, ++$b, --$b);

Results output

int(1)
int(0)
bool(true)
bool(true)

Boolean values are not affected ,NULL Increment to 1, Decrement to 0

edit /home/project/xcre.php

<?php

$a = 0;
$i = 'W';
while($a < 6) {
    
    echo "$a : ".++$i . PHP_EOL;
    $a++;
}

perform

php xcre.php

From the results, we can see

When dealing with the arithmetic operation of character variables ,PHP Followed Perl The habit of , Instead of C Of . for example

$a = 'Z';

// Perl  in 
$a++;// Will put  $a  become 'AA'

//C  in 
$a++;// Will put  $a  become  '['（'Z'  Of  ASCII  The value is  90,'['  Of  ASCII  The value is  91）

Note that character variables can only be incremented , Not decreasing , And only pure letters are supported （a-z and A-Z）. Increasing （ reduce ） Other character variables are not valid , The original string has not changed .

Logical operators

Common logical operators

• $a and $b, Logic and , If a and a and b All for TRUE
• $a && $b, Logic and , If a and a and b All for TRUE, among && Priority over and
• $a or $b, Logic or , If a or a or b Any for TRUE
• $a || $b, Logic or , If a or a or b Any for TRUE,|| Priority over or
• $a xor $b, Logical XOR , If a or a or b Any for TRUE, But not at the same time , Then return to TRUE
• ! $a, Logic is not , If $a Not for TRUE
  edit /home/project/logical.php

<?php

$a = (false && foo());
$b = (true  || foo());
$c = (false and foo());
$d = (true  or  foo());

var_dump($a, $b, $c, $d);

$e = false || true;
$f = false or true;

$g = true && false;
$h = true and false;

var_dump($e, $f, $g, $h);

perform

php logical.php

From the results, we can see

foo() Although there is no definition , But there is no chance to implement , Because the previous expression has determined the result ,foo() Short circuited .
&&,|| Has a higher priority than =,= Has a higher priority than and,or.

String operators

There are two string operators .

• The first is the join operator ., It returns the string connected by its left and right parameters
• The second is the join assignment operator .=, It appends the right parameter to the left parameter .

<?php
$a = "Hello ";
$b = $a . "World!"; // now $b contains "Hello World!"

$a = "Hello ";
$a .= "World!";     // now $a contains "Hello World!"

Click the environment window below , Start actual combat

Array operators

Common array operators

• $a + $b,a and a and b Union
• $a == $b,a and a and b If the key and value are the same, it is TRUE
• $a === $b,a and a and b Keys and values in the same order and type return TRUE
• $a != $b,a and a and b If the middle key or value is different, return TRUE
• $a <> $b, Equate to !=
• $a !== $b,a and a and b In the key , value , Order or type , If one of them is different, it returns TRUE
  edit /home/project/array.php

<?php

$a = ["a" => "apple", "b" => "banana"];
$b = ["a" => "pear", "b" => "strawberry", "c" => "cherry"];
$c = ["b" => "banana", "a" => "apple"];


var_dump($a + $b, $b + $a);
var_dump($a == $c, $a === $c);

perform

php array.php

It can be seen from the results

• Operator takes the array element on the right （ Remove those elements with the same key value as the array element on the left ） Append to the array on the left , However, duplicate key values will not be overwritten .
  ===, Array keys are required , value , The type and order are the same , To return to TRUE.

The execution operator

PHP Support an execution operator ： The quotation marks （``）. Note that this is not a single quotation mark ！PHP Will try to execute the contents of the backquote as a shell command , And return its output information to （ for example , You can assign a variable instead of simply discarding it to standard output ）.

<?php
$output = `ls -al`;
echo "<pre>$output</pre>";

Be careful , The backquote operator activates safe mode or turns off shell_exec() Time is invalid .

Error control operators

PHP Supports an error control operator ：@. When placing it in a PHP Before expression , Any error messages that this expression may generate are ignored .

<?php

$my_file = @file ('non_existent_file') or
    die ("Failed opening file: error was '$php_errormsg'");

$value = @$cache[$key];

Error control operators are only valid for expressions . A simple rule for beginners is ：

• If you can get value from somewhere , You can put... In front of it @ Operator . for example , You can put it in variables , Functions and include call , Constant , Wait, before .
• It cannot be placed before the definition of a function or class , Nor can it be used for conditional structures such as if and foreach etc. .

Be careful ： current @ The error control operator prefix invalidates even error reports of serious errors that cause the script to terminate .

This means that if you use... Before a function call that does not exist or has the wrong letter @ To suppress error messages , The script will show no sign of the cause of death there .

An operator

Bit operators allow evaluation and manipulation of the bits specified in an integer number .

$a & $b,And（ Bitwise AND ）, Will put a and a and b All of them are for 1 The bit of is set to 1.
$a | $b,Or（ Press bit or ）, Will put a and a and b Any one of them is 1 The bit of is set to 1.
$a ^ $b,Xor（Presspositiondifferentor）,takeholdaandaandbinOneindividualby1anotherOneindividualby0Ofpositionset\; upby1.$a,Not（ According to the not ）, take $a In Chinese, it means 0 The bit of is set to 1, vice versa .
$a << $b,Shift left（ Move left ）, take a The position in is shifted to the left a The position in is shifted to the left b Time （ Every move means multiplying by 2）.
$a >> $b,Shift right（ Move right ）, take a The position in moves to the right a The position in moves to the right b Time （ Every move is divided by 2）.
Example 1 The integer AND,OR and XOR An operator .

<?php
/* * Ignore the top section, * it is just formatting to make output clearer. */

$format = '(%1$2d = %1$04b) = (%2$2d = %2$04b)'
        . ' %3$s (%4$2d = %4$04b)' . "\n";

echo <<<EOH --------- --------- -- --------- result value op test --------- --------- -- --------- EOH;


/* * Here are the examples. */

$values = array(0, 1, 2, 4, 8);
$test = 1 + 4;

echo "\n Bitwise AND \n";
foreach ($values as $value) {
    
    $result = $value & $test;
    printf($format, $result, $value, '&', $test);
}

echo "\n Bitwise Inclusive OR \n";
foreach ($values as $value) {
    
    $result = $value | $test;
    printf($format, $result, $value, '|', $test);
}

echo "\n Bitwise Exclusive OR (XOR) \n";
foreach ($values as $value) {
    
    $result = $value ^ $test;
    printf($format, $result, $value, '^', $test);
}
?>

The above routine will output ：

---------     ---------  -- ---------
 result        value      op test
 ---------     ---------  -- ---------
 Bitwise AND
( 0 = 0000) = ( 0 = 0000) & ( 5 = 0101)
( 1 = 0001) = ( 1 = 0001) & ( 5 = 0101)
( 0 = 0000) = ( 2 = 0010) & ( 5 = 0101)
( 4 = 0100) = ( 4 = 0100) & ( 5 = 0101)
( 0 = 0000) = ( 8 = 1000) & ( 5 = 0101)

 Bitwise Inclusive OR
( 5 = 0101) = ( 0 = 0000) | ( 5 = 0101)
( 5 = 0101) = ( 1 = 0001) | ( 5 = 0101)
( 7 = 0111) = ( 2 = 0010) | ( 5 = 0101)
( 5 = 0101) = ( 4 = 0100) | ( 5 = 0101)
(13 = 1101) = ( 8 = 1000) | ( 5 = 0101)

 Bitwise Exclusive OR (XOR)
( 5 = 0101) = ( 0 = 0000) ^ ( 5 = 0101)
( 4 = 0100) = ( 1 = 0001) ^ ( 5 = 0101)
( 7 = 0111) = ( 2 = 0010) ^ ( 5 = 0101)
( 1 = 0001) = ( 4 = 0100) ^ ( 5 = 0101)
(13 = 1101) = ( 8 = 1000) ^ ( 5 = 0101)

PHP7 New operator

Combination comparator
The spacecraft operator uses <=> Express , Used to compare two expressions . When a Less than 、 Equal to or greater than a Less than 、 Equal to or greater than b When it returns to -1、0 or 1. The principle of comparison is to use PHP The regular comparison rules of .

<?php
//  Integers 
echo 1 <=> 1; // 0
echo 1 <=> 2; // -1
echo 2 <=> 1; // 1

//  Floating point numbers 
echo 1.5 <=> 1.5; // 0
echo 1.5 <=> 2.5; // -1
echo 2.5 <=> 1.5; // 1

//  character string 
echo "a" <=> "a"; // 0
echo "a" <=> "b"; // -1
echo "b" <=> "a"; // 1
?>

NULL coalescing operator
NULL The merge operator uses ?? Express , It means if ?? The previous variable exists and the value is not NULL, It will return its own value , Otherwise return to ?? Operand after .

<

?php

$username = $_GET['user'] ?? 'nobody';
$username = isset($_GET['user']) ? $_GET['user'] : 'nobody';

$username = $_GET['user'] ?? $_POST['user'] ?? 'nobody';

Merge operators can usually be replaced by ternary operators , Multiple merge operators are executed at one time from left to right .