PHP学习笔记-字符串操作一
PHP学习笔记-字符串操作1
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http://blog.csdn.net/hai_qing_xu_kong/article/details/51001820
本文出自：【顾林海的博客】
前言
这几天身体比较疲惫，看看晚上十点多了，还是把今天看的PHP知识点记录下来，由于一些客观原因，PHP每天只能看一点点，慢慢学习吧。
字符串简介
字符串是指由零个或多个字符构成的一个集合，这里所说的字符主要包含以下几种类型：
- 数字类型，如1、2、3等。
- 字母类型，如a、b、c、d等。
- 特殊字符，如#、$、%、^、&等。
- 不可见字符，如\n（换行符）、\r（回车符）、\t（Tab字符）等。
其中，不可见字符是比较特殊的一组字符，它用来控制字符串格式化输出，在浏览器上不可见，只能看到字符串输出的结果，如下：
<code class=" hljs xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>); <span class="hljs-keyword">echo</span> <span class="hljs-string">"pear\rapple\nbanan\tfruit"</span>;<span class="hljs-preprocessor">?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></code>
运行结果： pear apple banan fruit
发现并没有在浏览器上进行换行、回车之类的。 点击网页查看源代码：
单引号和双引号的区别
字符串通常以串的整体作为操作对象，一般用双引号或者单引号标识一个字符串。单引号和双引号在使用上有一定区别。对于定义的普通字符串看不出两者之间的区别。而通过对变量的处理，即可轻松地理解两者之间的区别。
<code>双引号中的内容是经过PHP的语法分析器解析过的，任何变量在双引号中都会被转换为它的值进行输出显示；而单引号的内容是“所见即所得”的，无论有无变量，都被当作普通字符串进行原样输出。</code>
<code class=" hljs xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>);<span class="hljs-variable">$str</span>=<span class="hljs-string">"PHP"</span>;<span class="hljs-variable">$str1</span>=<span class="hljs-string">"$str"</span>;<span class="hljs-variable">$str2</span>=<span class="hljs-string">'$str'</span>;<span class="hljs-keyword">echo</span> <span class="hljs-variable">$str1</span>.<span class="hljs-string">"<br>"</span>;<span class="hljs-keyword">echo</span> <span class="hljs-variable">$str2</span>;<span class="hljs-preprocessor">?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></code>
运行结果：
PHP
$str
技巧：单引号串和双引号串在PHP中的处理是不相同的。双引号串中的内容可以被解释并替换，而单引号串中的内容则只能被作为普通字符进行处理。
注意：在进行SQL查询之前，所有字符串都必须加单引号，以避免可能的注入漏洞和SQL错误。
字符串的连接符
半角句号“.”是字符串连接符，可以把两个或两个以上的字符串连接成一个字符串。 应用字符串连接符号无法实现大量简单字符串的连接，PHP允许程序员在双引号中直接包含字符串变量，当echo语句后面使用的是双引号（”）时，可以使用下面的格式来达到同样的效果。
<code class=" hljs xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-string"><?phpheader("</span>Content-Type:text/html; charset=gb2312<span class="hljs-string">");$str1="</span>Java<span class="hljs-string">";$str2="</span>PHP<span class="hljs-string">";echo "</span><span class="hljs-variable">$str1</span>,<span class="hljs-variable">$str2</span>,C++<span class="hljs-string">";?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></code>运行结果：
Java,PHP,C++
去除字符串首尾空格和特殊字符
用户在输入数据时，经常会在无意中输入多余的空格，在有些情况下，字符串中不允许出现空格和特殊字符，此时就需要去除字符串中的空格和特殊字符。在PHP中提供了trim()函数去除字符串左右两边的空格和特殊字符、ltrim()函数去除字符串左边的空格和特殊字符、rtrim()函数去除字符串中右边的空格和特殊字符。
1．trim()函数
trim()函数用于去除字符串开始位置以及结束位置的空格，并返回去掉空格后的字符串。
语法格式如下：
<code class=" hljs vbscript"><span class="hljs-built_in">string</span> <span class="hljs-built_in">trim</span>(<span class="hljs-built_in">string</span> str [,<span class="hljs-built_in">string</span> charlist]);</code>
trim()函数的参数str是要操作的字符串对象，参数charlist为可选参数，指定需要从指定的字符串中删除哪些字符，如果不设置该参数，则所有的可选字符都将被删除。
trim()函数的参数charlist的可选值如下表所示。
注意：除了以上默认的过滤字符列表外，也可以在charlist参数中提供要过滤的特殊字符。
使用trim()函数去除字符串左右两边的空格及特殊字符“\r\r(: :)”：
<code class=" hljs handlebars"><span class="xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>);<span class="hljs-variable">$str</span>=<span class="hljs-string">"\r\r(:@_@ 学习PHP @_@:) "</span>;<span class="hljs-keyword">echo</span> trim(<span class="hljs-variable">$str</span>);<span class="hljs-comment">//去除字符串左右两边的空格</span><span class="hljs-keyword">echo</span> <span class="hljs-string">"<br>"</span>;<span class="hljs-keyword">echo</span> trim(<span class="hljs-variable">$str</span>,<span class="hljs-string">"\r\r(: :)"</span>);<span class="hljs-comment">//去除字符串左右两边的特殊字符\r\r(::)</span><span class="hljs-preprocessor">?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></span></code>
运行结果：
(:@@ 学习PHP @@:)
@@ 学习PHP @@
2．Itrim()函数
Itrim()函数用于去除字符串左边的空格或者指定字符串。
语法格式如下：
string ltrim( string str [,string charlist]);
使用Itrim()函数去除字符串左边的空格及特殊字符“(:@[email protected]：
<code class=" hljs xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>);<span class="hljs-variable">$str</span>=<span class="hljs-string">" (:@_@ 学习PHP @_@:) "</span>;<span class="hljs-keyword">echo</span> trim(<span class="hljs-variable">$str</span>);<span class="hljs-comment">//去除字符串左边的空格</span><span class="hljs-keyword">echo</span> <span class="hljs-string">"<br>"</span>;<span class="hljs-keyword">echo</span> ltrim(<span class="hljs-variable">$str</span>,<span class="hljs-string">" (:@_@"</span>);<span class="hljs-comment">//去除字符串左边的特殊字符 (:@_@</span><span class="hljs-preprocessor">?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></code>
运行结果：
(:@@ 学习PHP @@:)
学习PHP @_@:)
3．rtrim()函数
rtrim()函数用于去除字符串右边的空格。
语法格式如下：
<code class=" hljs vbscript"><span class="hljs-built_in">String</span> <span class="hljs-built_in">rtrim</span>(<span class="hljs-built_in">string</span> str [,<span class="hljs-built_in">string</span> charlist]);</code>
使用rtrim()函数去除字符串右边的空格及特殊字符“@_@:)”：
<code class=" hljs handlebars"><span class="xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>);<span class="hljs-variable">$str</span>=<span class="hljs-string">" (:@_@ 学习PHP @_@:) "</span>;<span class="hljs-keyword">echo</span> trim(<span class="hljs-variable">$str</span>);<span class="hljs-comment">//去除字符串右边的空格</span><span class="hljs-keyword">echo</span> <span class="hljs-string">"<br>"</span>;<span class="hljs-keyword">echo</span> rtrim(<span class="hljs-variable">$str</span>,<span class="hljs-string">" @_@:)"</span>);<span class="hljs-comment">//去除字符串右边的特殊字符 @_@:)</span><span class="hljs-preprocessor">?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></span></code>
运行结果：
(:@@ 学习PHP @@:)
(:@_@ 学习PHP
转义、还原字符串数据
字符串转义、还原的方法有两种：一种是手动转义、还原字符串数据，另一种是自动转义、还原字符串数据。下面分别对这两种方法进行详细讲解。
1．手动转义、还原字符串数据
字符串可以用单引号（‘）、双引号（“”）、定界符（{}）3种方法定义。而指定一个简单字符串的最简单的方法是用单引号（‘）括起来。当使用字符串时，很可能在该串中存在这几种符号与PHP脚本混淆的字符，因此必须要做转义语句。这就要在它的前面使用转义符号“\”。
“\”是一个转义符，紧跟在“\”后面的第一个字符将变得没有意义或有特殊意义。如‘是字符串的定界符，写为\’时就失去了定界符的意义，变为了普通的单引号‘。读者可以通过echo ’\‘’;输出一个单引号‘，同时转义字符“\”也不会显示。
技巧1：如果要在字符串中表示单引号，则需要用反斜线（\）进行转义。例如，要表示字符串“I‘m”，则需要写成“I\’m”。
技巧2 ：对于简单的字符串建议采用手动方法进行字符串转义，而对于数据量较大的字符串，建议采用自动转义函数实现字符串的转义。
说明：手动转义字符串可应用addcslashes()函数进行字符串还原，其具体的实现方法将在下面进行介绍。
使用转义字符“\”对字符串进行转义：
<code class=" hljs xml"><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>);<span class="hljs-keyword">echo</span> <span class="hljs-string">'php,\'学习PHP\''</span>;<span class="hljs-preprocessor">?></span></span></code>
运行结果：
php,’学习PHP’
2．自动转义、还原字符串数据
自动转义、还原字符串数据可以应用PHP提供的addslashes()函数和stripslashes()函数实现。
1.addslashes()函数
addslashes()函数用来为字符串str加入斜线“\”。
语法格式如下：
<code class=" hljs cs"><span class="hljs-keyword">string</span> addslashes (<span class="hljs-keyword">string</span> str)</code>
2.stripslashes()函数
stripslashes()函数用来将使用addslashes()函数转义后的字符串str返回原样。
<code class=" hljs cs"><span class="hljs-keyword">string</span> stripslashes(<span class="hljs-keyword">string</span> str);</code>
使用自动转义字符addslashes()函数对字符串进行转义，然后使用stripslashes()函数进行还原：
<code class=" hljs xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>);<span class="hljs-variable">$str</span>=<span class="hljs-string">"php,'学习PHP'"</span>;<span class="hljs-keyword">echo</span> <span class="hljs-variable">$str</span>.<span class="hljs-string">"<br>"</span>;<span class="hljs-variable">$a</span>=addslashes(<span class="hljs-variable">$str</span>); <span class="hljs-comment">//对字符串中的特殊字符进行转义</span><span class="hljs-keyword">echo</span> <span class="hljs-variable">$a</span>.<span class="hljs-string">"<br>"</span>;<span class="hljs-variable">$b</span>=stripslashes(<span class="hljs-variable">$a</span>);<span class="hljs-comment">//对转义字符进行还原</span><span class="hljs-keyword">echo</span> <span class="hljs-variable">$b</span>;<span class="hljs-preprocessor">?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></code>
运行结果：
php,’学习PHP’
php,\’学习PHP\’
php,’学习PHP’
<code class=" hljs scss">技巧：所有数据在插入数据库之前，有必要应用<span class="hljs-function">addslashes()</span>函数进行字符串转义，以免特殊字符未经转义在插入数据库时出现错误。另外，对于使用<span class="hljs-function">addslashes()</span>函数实现的自动转义字符串可以使用<span class="hljs-function">stripcslashes()</span>函数进行还原，但数据在插入数据库之前必须再次进行转义。</code>
以上两个函数实现了对指定字符串进行自动转义和还原。除了上面介绍的方法外，还可以对要转义、还原的字符串进行一定范围的限制，通过使用addcslashes()函数和stripcslashes()函数实现对指定范围内的字符串进行自动转义、还原。下面分别对两个函数进行详细介绍。
3.addcslashes()函数
实现转义字符串中的字符，即在指定的字符charlist前加上反斜线。
语法格式如下：
<code class=" hljs cs"><span class="hljs-keyword">string</span> addcslashes (<span class="hljs-keyword">string</span> str, <span class="hljs-keyword">string</span> charlist)</code>
参数说明：
参数str为将要被操作的字符串，参数charlist指定在字符串中的哪些字符前加上反斜线“\”，如果参数charlist中包含\n、\r等字
符，将以C语言风格转换，而其他非字母数字且ASCII码低于32以及高于126的字符均转换成八进制表示。
注意：在定义参数charlist的范围时，需要明确在开始和结束的范围内的字符。
4.stripcslashes()函数
stripcslashes()函数用来将应用addcslashes()函数转义的字符串str还原。
语法格式如下：
<code class=" hljs cs"><span class="hljs-keyword">string</span> stripcslashes (<span class="hljs-keyword">string</span> str)</code>
使用addcslashes()函数对字符串进行转义，使用stripcslashes()函数对转义的字符串进行还原。
<code class=" hljs handlebars"><span class="xml"><span class="hljs-doctype"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"></span><span class="hljs-tag"><<span class="hljs-title">html</span> <span class="hljs-attribute">xmlns</span>=<span class="hljs-value">"http://www.w3.org/1999/xhtml"</span>></span><span class="hljs-tag"><<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">meta</span> <span class="hljs-attribute">http-equiv</span>=<span class="hljs-value">"Content-Type"</span> <span class="hljs-attribute">content</span>=<span class="hljs-value">"text/html; charset=gb2312"</span> /></span><span class="hljs-tag"><<span class="hljs-title">title</span>></span>PHP语言基础<span class="hljs-tag"></<span class="hljs-title">title</span>></span><span class="hljs-tag"></<span class="hljs-title">head</span>></span><span class="hljs-tag"><<span class="hljs-title">body</span>></span><span class="php"><span class="hljs-preprocessor"><?php</span>header(<span class="hljs-string">"Content-Type:text/html; charset=gb2312"</span>);<span class="hljs-variable">$str</span>=<span class="hljs-string">"学习PHP"</span>;<span class="hljs-keyword">echo</span> <span class="hljs-variable">$str</span>.<span class="hljs-string">"<br>"</span>;<span class="hljs-variable">$b</span>=addcslashes(<span class="hljs-variable">$str</span>,<span class="hljs-string">"学习PHP"</span>);<span class="hljs-keyword">echo</span> <span class="hljs-variable">$b</span>.<span class="hljs-string">"<br>"</span>;<span class="hljs-variable">$c</span>=stripcslashes(<span class="hljs-variable">$b</span>);<span class="hljs-keyword">echo</span> <span class="hljs-variable">$c</span>;<span class="hljs-preprocessor">?></span></span><span class="hljs-tag"></<span class="hljs-title">body</span>></span><span class="hljs-tag"></<span class="hljs-title">html</span>></span></span></code>
运行结果：
学习PHP
\321\247\317\260\P\H\P
学习PHP
技巧：在缓存文件中，一般对缓存数据的值采用addcslashes()函数进行指定范围的转义。
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