php字符串有哪几种定义方式

<?php
echo 'this is a simple string';
echo '<br>';

// 可以录入多行
echo 'You can also have embedded newlines in
strings this way as it is
okay to do';
echo '<br>';

// 输出： Arnold once said: "I'll be back"
echo 'Arnold once said: "I'll be back"';
echo '<br>';

// 输出： You deleted C:*.*?
echo 'You deleted C:\*.*?';
echo '<br>';

// 输出： You deleted C:*.*?
echo 'You deleted C:*.*?';
echo '<br>';

// 输出： This will not expand: n a newline
echo 'This will not expand: n a newline';
echo '<br>';

// 输出： Variables do not $expand $either
echo 'Variables do not $expand $either';
echo '<br>';
?>

<?php
echo "this is a simple string";
echo "<br>";

// 也可以录入多行
echo "You can also have embedded newlines in
strings this way as it is
okay to do";
?>

<?php
$str = <<<EOF
  url:
  https://www.uoften.com/
EOF;
echo $str;
?>

<?php
// 无缩进
echo <<<END
      a
     b
    c
n
END;
// 4 空格缩进
echo <<<END
      a
     b
    c
    END;

<?php
echo <<<END
  a
 b
c
   END;

PHP Parse error:  Invalid body indentation level (expecting an indentation level of at least 3) in example.php on line 4

<?php
// 以下所有代码都不起作用。
// 正文（空格）和结束标记（制表符），不同的缩进
{
    echo <<<END
     a
        END;
}
// 在正文中混合空格和制表符
{
    echo <<<END
        a
     END;
}
// 在结束标记中混合空格和制表符
{
    echo <<<END
          a
         END;
}

PHP Parse error:  Invalid indentation - tabs and spaces cannot be mixed in example.php line 8

<?php
$values = [<<<END
a
  b
    c
END, 'd e f'];
var_dump($values);

array(2) {
  [0] =>
  string(11) "a
  b
    c"
  [1] =>
  string(5) "d e f"
}

<?php
echo <<<'EOD'
Example of string spanning multiple lines
using nowdoc syntax. Backslashes are always treated literally,
e.g. \ and '.
EOD;

<?php

/* 含有变量的更复杂的示例 */
class foo
{
    public $foo;
    public $bar;

    function __construct()
    {
        $this->foo = 'Foo';
        $this->bar = array('Bar1', 'Bar2', 'Bar3');
    }
}

$foo = new foo();
$name = 'MyName';

echo <<<'EOT'
My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should not print a capital 'A': x41
EOT;
?>

<?php
$juice = "apple";

echo "He drank some $juice juice.".PHP_EOL;
// Invalid. "s" is a valid character for a variable name, but the variable is $juice.
echo "He drank some juice made of $juices.";
// Valid. Explicitly specify the end of the variable name by enclosing it in braces:
echo "He drank some juice made of ${juice}s.";
?>

<?php
$juices = array("apple", "orange", "koolaid1" => "purple");

echo "He drank some $juices[0] juice.".PHP_EOL;
echo "He drank some $juices[1] juice.".PHP_EOL;
echo "He drank some $juices[koolaid1] juice.".PHP_EOL;

class people {
    public $john = "John Smith";
    public $jane = "Jane Smith";
    public $robert = "Robert Paulsen";

    public $smith = "Smith";
}

$people = new people();

echo "$people->john drank some $juices[0] juice.".PHP_EOL;
echo "$people->john then said hello to $people->jane.".PHP_EOL;
echo "$people->john's wife greeted $people->robert.".PHP_EOL;
echo "$people->robert greeted the two $people->smiths."; // Won't work
?>

<?php
$string = 'string';
echo "The character at index -2 is $string[-2].", PHP_EOL;
$string[-3] = 'o';
echo "Changing the character at index -3 to o gives $string.", PHP_EOL;
?>

<?php
// 显示所有错误
error_reporting(E_ALL);

$great = 'fantastic';

// 无效，输出: This is { fantastic}
echo "This is { $great}";

// 有效，输出： This is fantastic
echo "This is {$great}";

// 有效
echo "This square is {$square->width}00 centimeters broad.";

// 有效，只有通过花括号语法才能正确解析带引号的键名
echo "This works: {$arr['key']}";

// 有效
echo "This works: {$arr[4][3]}";

// 这是错误的表达式，因为就象 $foo[bar] 的格式在字符串以外也是错的一样。
// 换句话说，只有在 PHP 能找到常量 foo 的前提下才会正常工作；这里会产生一个
// E_NOTICE (undefined constant) 级别的错误。
echo "This is wrong: {$arr[foo][3]}";

// 有效，当在字符串中使用多重数组时，一定要用括号将它括起来
echo "This works: {$arr['foo'][3]}";

// 有效
echo "This works: " . $arr['foo'][3];

echo "This works too: {$obj->values[3]->name}";

echo "This is the value of the var named $name: {${$name}}";

echo "This is the value of the var named by the return value of getName(): {${getName()}}";

echo "This is the value of the var named by the return value of $object->getName(): {${$object->getName()}}";

// 无效，输出： This is the return value of getName(): {getName()}
echo "This is the return value of getName(): {getName()}";

// 无效, 输出： C:folder{fantastic}.txt
echo "C:folder{$great}.txt"
// 有效, 输出： C:folderfantastic.txt
echo "C:\folder\{$great}.txt"
?>

<?php
class foo {
    var $bar = 'I am bar.';
}

$foo = new foo();
$bar = 'bar';
$baz = array('foo', 'bar', 'baz', 'quux');
echo "{$foo->$bar}n";
echo "{$foo->{$baz[1]}}n";
?>