在字符串中添加带下划线的大写字符

Question

I am trying to convert a string e.g. WhatAWonderfulDay into a lowercase string where all uppercase characters are preceded with underscores e.g. what_a_wonderful_day. Also, I am trying to make a reverse algorithm that translates let's say a_quick_fox into AQuickFox.

I am providing my implementation, though I know it's inefficient. Any ways to simplify these two operations?

// 1. WhatAWonderfulDay -> what_a_wonderful_day

$chars = str_split('WhatAWonderfulDay');
$result = "";
foreach($chars as $char) {
    if (ctype_upper($char) && !empty($result))
        $result .= "_"
    $result .= $char;
}
echo $result;

// 2. a_quick_fox => AQuickFox

$chars = str_split('a_quick_fox');

$result = "";
$should_make_upper = true;
foreach($chars as $char) {
    $result .= (should_make_upper) ? strtoupper($char) : $char;
    $should_make_upper = false;
    if ($char == "_")
        $should_make_upper = true;
}
echo $result;

Answer 1

Here is some simpel code that will get you started:

$string = "AQuickTest";

preg_match_all("/[A-Z]/",$string,$matches);

foreach($matches[0] as $match){
    $string = str_replace($match,"_".strtolower($match),$string);
}

echo $string;

The result is: _a_quick_test