PHP中的string类型使用说明

鉴于大家对PHP十分关注，我们编辑小组在此为大家搜集整理了“PHP中的string类型使用说明”一文，供大家参考学习!

注意：PHP没有对string的长度做限制。唯一限制的就是PHP在计算机中的可用内存（php.ini文件中的memory_limit变量的值)
限定字符串范围的方法有4中：
1、单引号；
2、双引号；
3、原型文档语法；
4、nowdoc syntax（PHP5.3.0开始）

1、如果字符串使用单引号“‘”包裹，字符串中如果出现单引号“，”和反斜杠“\”符号，需要进行转义。
复制代码 代码如下:
// Outputs: Arnold once said: "I''ll be back"
echo ''Arnold once said: "I\''ll be back"'';
// Outputs: You deleted C:\*.*?
echo ''You deleted C:\\*.*?'';
// Outputs: You deleted C:\*.*?
echo ''You deleted C:\*.*?'';

（有待验证 单引号包裹的字符串反斜杠是否需要转义）

2、如果字符串被双引号包裹 一下字符都会被转义：
Escaped characters Sequence Meaning
\n linefeed (LF or 0x0A (10) in ASCII)
\r carriage return (CR or 0x0D (13) in ASCII)
\t horizontal tab (HT or 0x09 (9) in ASCII)
\v vertical tab (VT or 0x0B (11) in ASCII) (since PHP 5.2.5)
\f form feed (FF or 0x0C (12) in ASCII) (since PHP 5.2.5)
\\ backslash
\$ dollar sign
\" double-quote
\[0-7]{1,3} the sequence of characters matching the regular expression is a character in octal notation
\x[0-9A-Fa-f]{1,2} the sequence of characters matching the regular expression is a character in hexadecimal notation

如果字符串 使用双引号“"”或者原形文档语法的形式包裹的话，在字符串中的变量会被解析。
1、简单语法：
因为解析器会贪婪匹配$后面的字符，所以，为了不出什么以外，应该使用"{"和"}"来表名变量的边界。
复制代码 代码如下:
<?php
$beer = ''Heineken'';
echo "$beer''s taste is great"; // works; "''" is an invalid character for variable names
echo "He drank some $beers"; // won''t work; ''s'' is a valid character for variable names but the variable is "$beer"
echo "He drank some ${beer}s"; // works
echo "He drank some {$beer}s"; // works
?>

同样，数组的下标和对象的属性也会不解析。
复制代码 代码如下:
<?php
// These examples are specific to using arrays inside of strings.
// When outside of a string, always quote array string keys and do not use
// {braces}.
// Show all errors
error_reporting(E_ALL);
$fruits = array(''strawberry'' => ''red'', ''banana'' => ''yellow'');
// Works, but note that this works differently outside a string
echo "A banana is $fruits[banana].";
// Works
echo "A banana is {$fruits[''banana'']}.";
// Works, but PHP looks for a constant named banana first, as described below.
echo "A banana is {$fruits[banana]}.";
// Won''t work, use braces. This results in a parse error.
echo "A banana is $fruits[''banana''].";
// Works
echo "A banana is " . $fruits[''banana''] . ".";
// Works
echo "This square is $square->width meters broad.";
// Won''t work. For a solution, see the complex syntax.
echo "This square is $square->width00 centimeters broad.";
?>

2、复合语法:
复制代码 代码如下:
<?php
// Show all errors
error_reporting(E_ALL);
$great = ''fantastic'';
// Won''t work, outputs: This is { fantastic}
echo "This is { $great}";
// Works, outputs: This is fantastic
echo "This is {$great}";
echo "This is ${great}";
// Works
echo "This square is {$square->