The difference between mb_ series functions and ordinary character functions

The

mb function is a function extension that processes text according to the encoding format.

Modify the /etc/php.ini configuration file and add extension=php_mbstring.so

Let’s use my most commonly used substr function as an example. It's clear at a glance.

Example:

<span style="color: #008080"> 1</span> <span style="color: #000000">php
</span><span style="color: #008080"> 2</span>         <span style="color: #008000">//</span><span style="color: #008000">phpinfo();</span>
<span style="color: #008080"> 3</span>         <span style="color: #800080">$str</span> = 'abcdef'<span style="color: #000000">;
</span><span style="color: #008080"> 4</span>         <span style="color: #0000ff">echo</span> <span style="color: #008080">strlen</span>(<span style="color: #800080">$str</span>);<span style="color: #008000">//</span><span style="color: #008000"> 6</span>
<span style="color: #008080"> 5</span>         <span style="color: #0000ff">echo</span> '<br>'<span style="color: #000000">;
</span><span style="color: #008080"> 6</span>         <span style="color: #0000ff">echo</span> <span style="color: #008080">substr</span>(<span style="color: #800080">$str</span>, 1,2);<span style="color: #008000">//</span><span style="color: #008000"> bc</span>
<span style="color: #008080"> 7</span>         <span style="color: #0000ff">echo</span> '<br>'<span style="color: #000000">;
</span><span style="color: #008080"> 8</span> 
<span style="color: #008080"> 9</span>         <span style="color: #800080">$str2</span> = '我是谁ab'<span style="color: #000000">;
</span><span style="color: #008080">10</span>         <span style="color: #0000ff">echo</span> <span style="color: #008080">substr</span>(<span style="color: #800080">$str2</span>, 2, 2);<span style="color: #008000">//</span><span style="color: #008000"> ��</span>
<span style="color: #008080">11</span>         <span style="color: #0000ff">echo</span> '<br>'<span style="color: #000000">;
</span><span style="color: #008080">12</span>         <span style="color: #0000ff">echo</span> mb_substr(<span style="color: #800080">$str2</span>, 2, 2, 'UTF-8');<span style="color: #008000">//</span><span style="color: #008000"> 谁a</span>
<span style="color: #008080">13</span>         <span style="color: #0000ff">echo</span> '<br>'<span style="color: #000000">;
</span><span style="color: #008080">14</span>         <span style="color: #0000ff">echo</span> <span style="color: #008080">strlen</span>(<span style="color: #800080">$str2</span>);<span style="color: #008000">//</span><span style="color: #008000"> 11</span>
<span style="color: #008080">15</span>         <span style="color: #0000ff">echo</span> '<br>'<span style="color: #000000">;
</span><span style="color: #008080">16</span>         <span style="color: #0000ff">echo</span> mb_strlen(<span style="color: #800080">$str2</span>, 'UTF-8');<span style="color: #008000">//</span><span style="color: #008000"> 5</span>
<span style="color: #008080">17</span>         <span style="color: #0000ff">echo</span> '<br>';

Look at lines 10 and 12, the effect is clear.