[PHP source code reading] strtolower and strtoupper functions, strtoupper_PHP tutorial

[PHP source code reading] strtolower and strtoupper functions, strtoupper

Among the string operation functions, string case conversion is also a relatively commonly used function, and its underlying implementation is also It’s relatively simple, let’s find out below.

I have more detailed annotations on the PHP source code on github. If you are interested, you can take a look and give it a star. PHP5.4 source code annotations. You can view the added annotations through the commit record.

strtolower

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

Convert the string to lowercase characters.

strtoupper

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

Convert the string to uppercase characters.

Run the example

<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>

Code running steps

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

Source code interpretation

The core operations of the two functions are similar. Let’s talk about strtolower, the other one is similar.
The core code of the php_strtolower function is as follows:

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;

This function traverses the entire string and converts it into lowercase characters one by one. This is also a classic pointer operation.

Original article with limited writing style and limited knowledge. If there is anything wrong in the article, please let me know.

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