[PHP源码阅读]strtolower和strtoupper函数，strtoupper

<p>string strtolower ( string $string )</p>

<p>string strtoupper ( string $string )</p><p><span>立即学习</span>“<a href="https://pan.quark.cn/s/7fc7563c4182" style="text-decoration: underline !important; color: blue; font-weight: bolder;" rel="nofollow" target="_blank">PHP免费学习笔记（深入）</a>”；</p>

<span>$str</span> = 'Hello World'<span>;
</span><span>$new_str</span> = <span>strtolower</span>(<span>$str</span>); <span>//</span><span> hello world</span>

<span>$str</span> = 'hello world'<span>;
</span><span>$new_str</span> = strupper(<span>$str</span>); <span>//</span><span> HELLO WORLD</span>

<p>拷贝一份字符串</p>
<p>php_strtolower/php_strtoupper进行转换</p>

c = (unsigned <span>char</span> *<span>)s;
e </span>= c+<span>len;

</span><span>//</span><span> 遍历s，逐个变为小写</span>
<span>while</span> (c <<span> e) {
　　</span>*c = tolower(*<span>c);
　　c</span>++<span>;
}
</span><span>return</span> s;