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->width}00 centimeters broad.";
// works
echo "this works: {$arr[4][3]}";
// this is wrong for the same reason as $foo[bar] is wrong outside a string.
// in other words, it will still work, but only because php first looks for a
// constant named foo; an error of level e_notice (undefined constant) will be
// thrown.
echo "this is wrong: {$arr[foo][3]}";
// works. when using multi-dimensional arrays, always use braces around arrays
// when inside of strings
echo "this works: {$arr['foo'][3]}";
// works.
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()}}";
访问,修改字符串中的指定字符：
字符串可以使用"[]"和"{}"进行访问。（注意：php5.3.0以后不建议使用“｛｝”访问）
注意：使用其他类型（非integer）类型访问字符串指定的字符，都会返回null
警告：
writing to an out of range offset pads the string with spaces. non-integer types are converted to integer. illegal offset type emits e_notice. negative offset emits e_notice in write but reads empty string. only the first character of an assigned string is used. assigning empty string assigns nul byte。
【说明】：本文章由站长整理发布，文章内容不代表本站观点，如文中有侵权行为，请与本站客服联系(QQ:)！