In-depth understanding of PHP string functions_PHP tutorial

We all know that no matter which language, string operation is an important foundation, often simple and important. Just like human speech, it generally has a form (graphical interface) and language (print string?). Obviously strings can explain more things. PHP provides a large number of string operation functions, which are powerful and relatively simple to use. The following will briefly describe the functions and characteristics of PHP string functions.

PHP string function weak type

PHP is a weakly typed language, so other types of data can generally be directly applied to string operation functions and automatically converted into String type is processed, such as: echo substr("1234567", 1, 3); and echo substr(123456,1, 3); are the same definition. Generally, double quotes or single quotes are used to identify a string. For example, there are some differences between

<ol class="dp-xml">
<li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">str</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">"i love u"</font></span><span>;  </span></span></li>
<li class="">
<span>$</span><span class="attribute"><font color="#ff0000">str</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">'i love u'</font></span><span>; </span>
</li>
</ol>

and others. The latter treats all single quotation marks as characters; the former does not. For example,

<ol class="dp-xml">
<li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">test</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">"iwind"</font></span><span>;  </span></span></li>
<li class="">
<span>$</span><span class="attribute"><font color="#ff0000">str</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">"i love $test"</font></span><span>;  </span>
</li>
<li class="alt">
<span>$</span><span class="attribute"><font color="#ff0000">str1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">'i love $test'</font></span><span>;  </span>
</li>
<li class=""><span>echo $str; //将得到 i love iwind  </span></li>
<li class="alt"><span>echo $str1; //将得到 i love $test </span></li>
</ol>

The behavior of the following two examples is also different:

<ol class="dp-xml">
<li class="alt"><span><span>echo "i love test"; // 将得到 i love est,已经将t视为转义  </span></span></li>
<li class=""><span>echo 'i love test'; // 将得到 i love test </span></li>
</ol>

So you can simply think of double quotes The content inside is "explained", and the single quotes are "what you see is what you get" (in particular, '' will be recognized as a ''). Obviously, the double quotation mark form is more flexible. Of course, single quotation marks will be suitable for some special occasions, which will not be explained here. The most commonly used methods for outputting output in PHP are echo and print. Neither of them are real functions, but language constructs, so there is no need to use double brackets when calling (such as echo("test");print("test")). Both can achieve assignment when outputting: echo $str="test"; on the one hand, it outputs test, and on the other hand, it assigns "test" to the string variable $strprint $str="test"; except for the name, the two are different. Besides, there are other differences. Print has a return value and always returns 1, but echo does not, so echo is faster than print:

<ol class="dp-xml">
<li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">return</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">print</font></span><span> "test";  </span></span></li>
<li class=""><span>echo $return; // 输出1 </span></li>
</ol>

For this reason, print can be used in compound statements, but echo cannot:

<ol class="dp-xml">
<li class="alt"><span><span>isset($str) or print "str 变量未定义"; // 将输出"str 变量未定义"  </span></span></li>
<li class=""><span>isset($str) or echo "str 变量未定义";// 将提示分析错误  </span></li>
<li class="alt"><span>echo一次可输出多个字符串，而print则不可以：  </span></li>
<li class=""><span>echo "i ","love ","iwind"; // 将输出 "i love iwind"  </span></li>
<li class="alt"><span>print "i ","love ","iwind"; // 将提示错误  </span></li>
<li class=""><span>echo,print还可以输出被称作“文档句法”的字符串，句法如:  </span></li>
<li class="alt">
<span>echo </span><strong><font color="#006699"><span class="tag"><</span><span class="tag"><</span><span class="tag"><</span></font></strong><span> 标签名称 </span>
</li>
</ol>

PHP string function content tag name; such as

<ol class="dp-xml">
<li class="alt"><span><span>echo </span><strong><font color="#006699"><span class="tag"><</span><span class="tag"><</span><span class="tag"><</span></font></strong><span> </span><span class="tag-name"><strong><font color="#006699">test</font></strong></span><span> </span></span></li>
<li class=""><span>i love iwind  </span></li>
<li class="alt"><span>test; </span></li>
</ol>

. It should be noted that the two tag names at the beginning and end of the statement are the same, and there cannot be before the latter tag name. If it is blank, it must be written in top format. The content of the document syntax output identifies variable names and common symbols, which is roughly the same as the function of double quotes. In addition to outputting echo and print, PHP also provides some functions for formatting strings, such as printf, sprintf, vprintf, vsprintf, which will not be explained in detail here.

http://www.bkjia.com/PHPjc/446472.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/446472.htmlTechArticleWe all know that no matter which language, string operation is an important foundation, often simple and important. Just like when people speak, they generally have form (graphical interface) and language (...