The differences and characteristics between php heredoc and nowdoc-PHP Tutorial-php.cn

The differences and characteristics between php heredoc and nowdoc

jacklove

Release： 2023-03-31 09:10:01

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php heredoc and nowdoc

heredoc structure

heredoc syntax Structure: <<<. After the operator, provide an identifier and then a newline. Next comes the string itself, ending with the previously defined identifier.

<?php
$content = <<<FDIPZONE
<html>
<head>
<title>test</title>
</head>
<body>
<p><img src="http://www.csdn.net/css/logo.png"></p>
<p><a href=&#39;http://blog.csdn.net/fdipzone&#39;>blog</a></p>
</body>
</html>
FDIPZONE;
echo $content;
?>

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The heredoc structure cannot be used to initialize properties of a class. As of PHP 5.3, this restriction only applies when the heredoc contains variables. The following example will go wrong.

<?php
class test{
public $var = &#39;123&#39;;
public $a = <<<FDIPZONE
$var
FDIPZONE;
}
$obj = new test();
echo $obj->a;
?>

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In the heredoc structure, variables will be replaced, but methods will not. Be careful when containing complex variables.

<?php
$var = &#39;123&#39;;
$content = <<<FDIPZONE
$var time();
FDIPZONE;
echo $content; // 123 time();
?>

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nowdoc structure

##nowdoc syntactic structure is very similar to the heredoc structure, but in nowdoc No parsing operation is performed. This structure is suitable for embedding PHP code or other large pieces of text without escaping special characters.

nowdoc The same tags <<< as in the heredoc structure, but the identifier following must be enclosed in single quotes, that is, <<<'EOF'. All the rules for heredoc structures also apply to nowdoc structures, especially the rules for terminating identifiers. nowdoc was added after php5.3.

<?php
$var = &#39;123&#39;;
$content = <<<&#39;FDIPZONE&#39;
$var time();
FDIPZONE;
echo $content; // $var time(); $var没有被替换
?>

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nowdoc structure can be used in any static data environment. The most typical example is to initialize properties or constants of a class. The following example will not go wrong, you can compare it with the heredoc example.

<?php
class test{
public $a = <<<&#39;FDIPZONE&#39;
$var
FDIPZONE;
}
$obj = new test();
echo $obj->a;
?>

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