PHP中奇妙的String
字符串的表示
PHP中字符串的表示可以用双引号，也可以用单引号，但是两者之间有些区别。
- 字符串中有变量的时候，单引号仅输出变量名，而不是值：
<div> <span style="color: #008080;">1</span> <span style="color: #000000;"> </span><span style="color: #000000;"></span><span style="color: #000000;">php<br></span><span style="color: #008080;">2</span> <span style="color: #000000;"> </span><span style="color: #800080;">$color</span><span style="color: #000000;"> </span><span style="color: #000000;">=</span><span style="color: #000000;"> </span><span style="color: #000000;">"</span><span style="color: #000000;">red</span><span style="color: #000000;">"</span><span style="color: #000000;">;<br></span><span style="color: #008080;">3</span> <span style="color: #000000;"> </span><span style="color: #0000ff;">echo</span><span style="color: #000000;"> </span><span style="color: #000000;">"</span><span style="color: #000000;">Roses are</span><span style="color: #800080;">$color</span><span style="color: #000000;">"</span><span style="color: #000000;">;<br></span><span style="color: #008080;">4</span> <span style="color: #000000;"> </span><span style="color: #0000ff;">echo</span><span style="color: #000000;"> </span><span style="color: #000000;">"</span><span style="color: #000000;"><br></span><span style="color: #000000;">"</span><span style="color: #000000;">;<br></span><span style="color: #008080;">5</span> <span style="color: #000000;"> </span><span style="color: #0000ff;">echo</span><span style="color: #000000;"> </span><span style="color: #000000;">'</span><span style="color: #000000;">Roses are $color</span><span style="color: #000000;">'</span><span style="color: #000000;">;<br></span><span style="color: #008080;">6</span> <span style="color: #000000;"> </span><span style="color: #000000;">?></span> </div>
输出：
<div> <span style="color: #000000;">Roses are red<br>Roses are</span><span style="color: #800080;">$color</span> </div>
- 转义字符：
"\t" 输出时就是制表符， 而‘\t' 就是直接输出 \t 了。
在window下 "\r\n" 是表示换行，可是。。。
- 此外，在PHP中要输出一个换行的时候，只能用“
”，可能这也是它与HTML语言高度结合的结果吧。
字符串的拼接
在java中，我们用加号运算符“+”来连接字符串。
在 PHP 中，请使用这个点运算符 (.) ：
<div> <span style="color: #008080;">1</span> <span style="color: #000000;"></span><span style="color: #000000;">php<br></span><span style="color: #008080;">2</span> <span style="color: #000000;"> </span><span style="color: #800080;">$txt1</span><span style="color: #000000;">=</span><span style="color: #000000;">"</span><span style="color: #000000;">Hello World</span><span style="color: #000000;">"</span><span style="color: #000000;">;<br></span><span style="color: #008080;">3</span> <span style="color: #000000;"> </span><span style="color: #800080;">$txt2</span><span style="color: #000000;">=</span><span style="color: #000000;">"</span><span style="color: #000000;">1234</span><span style="color: #000000;">"</span><span style="color: #000000;">;<br></span><span style="color: #008080;">4</span> <span style="color: #000000;"> </span><span style="color: #0000ff;">echo</span><span style="color: #000000;"> </span><span style="color: #800080;">$txt1</span><span style="color: #000000;"> </span><span style="color: #000000;">.</span><span style="color: #000000;"> </span><span style="color: #000000;">"</span><span style="color: #000000;"> </span><span style="color: #000000;">"</span><span style="color: #000000;"> </span><span style="color: #000000;">.</span><span style="color: #000000;"> </span><span style="color: #800080;">$txt2</span><span style="color: #000000;">;<br></span><span style="color: #008080;">5</span> <span style="color: #000000;"> </span><span style="color: #000000;">?></span> </div>
字符串的输出
在PHP中， 我们一般用echo来输出字符串。
<div> <span style="color: #008080;">1</span> <span style="color: #000000;"></span><span style="color: #000000;">php<br></span><span style="color: #008080;">2</span> <span style="color: #000000;"> </span><span style="color: #0000ff;">echo</span><span style="color: #000000;"> </span><span style="color: #000000;">"</span><span style="color: #000000;">This text<br></span><span style="color: #008080;">3</span> <span style="color: #000000;">spans multiple<br></span><span style="color: #008080;">4</span> <span style="color: #000000;">lines.</span><span style="color: #000000;">"</span><span style="color: #000000;">;<br></span><span style="color: #008080;">5</span> <span style="color: #000000;"> </span><span style="color: #000000;">?></span> </div>
<div> <span style="color: #000000;">This text spans multiple lines</span><span style="color: #000000;">.</span> </div>
Echo的简化语法：（可以跟jsp中插入java变量的用法做个比较）
<div> <span style="color: #008080;">1</span> <span style="color: #000000;"><span style="color: #000000;">html</span><span style="color: #000000;">></span><span style="color: #000000;"><br></span><span style="color: #008080;">2</span> <span style="color: #000000;"> </span><span style="color: #000000;"><span style="color: #000000;">body</span><span style="color: #000000;">></span><span style="color: #000000;"><br></span><span style="color: #008080;">3</span> <span style="color: #000000;"> </span><span style="color: #000000;"></span><span style="color: #000000;">php<br></span><span style="color: #008080;">4</span> <span style="color: #000000;"> </span><span style="color: #800080;">$color</span><span style="color: #000000;"> </span><span style="color: #000000;">=</span><span style="color: #000000;"> </span><span style="color: #000000;">"</span><span style="color: #000000;">red</span><span style="color: #000000;">"</span><span style="color: #000000;">;<br></span><span style="color: #008080;">5</span> <span style="color: #000000;"> </span><span style="color: #000000;">?></span><span style="color: #000000;"><br></span><span style="color: #008080;">6</span> <span style="color: #000000;"><br></span><span style="color: #008080;">7</span> <span style="color: #000000;"> </span><span style="color: #000000;"><span style="color: #000000;">p</span><span style="color: #000000;">></span><span style="color: #000000;">Roses are </span><span style="color: #000000;">=</span><span style="color: #800080;">$color</span><span style="color: #000000;">?></span><span style="color: #000000;">p</span><span style="color: #000000;">></span><span style="color: #000000;"><br></span><span style="color: #008080;">8</span> <span style="color: #000000;"> </span><span style="color: #000000;"></span><span style="color: #000000;">body</span><span style="color: #000000;">></span><span style="color: #000000;"><br></span><span style="color: #008080;">9</span> <span style="color: #000000;"> </span><span style="color: #000000;"></span><span style="color: #000000;">html</span><span style="color: #000000;">></span></span></span></span> </div>
当然还有其他输出方式:print 以及printf（用于控制输出格式）。但是echo的输出速度是最快的。
字符串处理函数
PHP也提供与其他语言类似的字符串处理函数，常用的有：
chr() 从指定的 ASCII 值返回字符。
explode() 把字符串打散为数组。
str_ireplace() 替换字符串中的一些字符。（对大小写不敏感）
str_word_count() 计算字符串中的单词数。
strip_tags() 剥去 HTML、XML 以及 PHP 的标签。
stripos() 返回字符串在另一字符串中第一次出现的位置(大小写不敏感)
strlen() 返回字符串的长度。
htmlspecialchars_decode() 把一些预定义的 HTML 实体转换为字符。（可参考：http://cipw.blog.163.com/blog/static/16189330720103812949625/ ）
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