What is the concept of string in PHP

stay php What is the concept of string in

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stay php in , A string is a continuous sequence of characters , Consists of a series of characters , Each character is equivalent to a byte . There are three ways to define a string ：1、 Wrap the characters in single quotation marks , grammar “' String content '”;2、 Wrap the characters in double quotation marks , grammar “" String content "”;3、 Use heredoc syntactic structure “<<<”, grammar “<<<EOF Character content EOF;”.

The operating environment of this tutorial ：windows7 System 、PHP8.1 edition 、DELL G3 The computer

php String in

A string is a continuous sequence of characters , Consists of a series of characters , Each character is equivalent to a byte .

In other languages , Characters and strings are two different data types , But in PHP in , Treat characters and strings as string data types .

stay PHP in , There are three ways to define a string , These are the single quotation marks 、 Double quotation marks 、Heredoc The way .

Use single quotation marks to define the string

The easiest way to define a string is to enclose it in single quotes （ character '）.

To express a single quotation mark itself , It needs to be preceded by a backslash （\） To escape . To express a backslash itself , Use two backslashes （\\）. Any other backslash will be treated as the backslash itself ： That is, if you want to use other escape sequences, such as \r perhaps \n, Does not mean anything special , Just the two characters themselves .

<?phpecho 'this is a simple string';echo '<br>';//  You can enter multiple lines echo 'You can also have embedded newlines instrings this way as it isokay to do';echo '<br>';//  Output ： Arnold once said: "I'll be back"echo 'Arnold once said: "I\'ll be back"';echo '<br>';//  Output ： You deleted C:\*.*?echo 'You deleted C:\\*.*?';echo '<br>';//  Output ： You deleted C:\*.*?echo 'You deleted C:\*.*?';echo '<br>';//  Output ： This will not expand: \n a newlineecho 'This will not expand: \n a newline';echo '<br>';//  Output ： Variables do not $expand $eitherecho 'Variables do not $expand $either';echo '<br>';?>

Use double quotation marks to define the string

If the string is enclosed in double quotes （"） in , PHP The following special characters will be parsed ：

Escape character

Sequence	meaning
\n	Line break （ASCII In the character set LF or 0x0A (10)）
\r	enter （ASCII In the character set CR or 0x0D (13)）
\t	Horizontal tabs （ASCII In the character set HT or 0x09 (9)）
\v	Vertical tabs （ASCII In the character set VT or 0x0B (11)）
\e	Escape（ASCII In the character set ESC or 0x1B (27)）
\f	Change the page （ASCII In the character set FF or 0x0C (12)）
\\	Backslash
\$	Dollar sign
\"	Double quotes
\[0-7]{1,3}	What matches the regular expression sequence is a character expressed in octal ,which silently overflows to fit in a byte        (e.g. "\400" === "\000")
\x[0-9A-Fa-f]{1,2}	What matches the regular expression sequence is a character expressed in hexadecimal
\u{[0-9A-Fa-f]+}	The sequence of characters matching the regular expression is unicode Code bits ,         This code bit can be used as UTF-8 The expression of the output string

Just like a single quote string , Escaping any other character will cause the backslash to be displayed .

<?phpecho "this is a simple string";?>

Heredoc structure

The third way to express a string is to use heredoc syntactic structure ：<<<. Provide an identifier after the operator , And then line break . Next is the string string In itself , Finally, use the identifier defined above as the end flag .

End identifiers can use spaces or tabs （tab） Indent , The document string removes all indents . stay PHP 7.3.0 In the previous version , The identifier referenced at the end must be in the first column of the row .

and , The naming of identifiers should also be followed like other tags PHP The rules of ： Can only contain letters 、 Numbers and underscores , And must start with a letter and an underscore .

Example 1

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

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