How to convert PascalCase to pascal_case?

Question

If I had:

$string = \"PascalCase\";

I need

\"pascal_case\"

Does PHP offer a function for this purpose?

Answer 1

You need to run a regex through it that matches every uppercase letter except if it is in the beginning and replace it with underscrore plus that letter. An utf-8 solution is this:

header('content-type: text/html; charset=utf-8');
$separated = preg_replace('%(?

If you are not sure what case your string is, better to check it first, because this code assumes that the input is camelCase instead of underscore_Case or dash-Case, so if the latters have uppercase letters, it will add underscores to them.

The accepted answer from cletus is way too overcomplicated imho and it works only with latin characters. I find it a really bad solution and wonder why it was accepted at all. Converting TEST123String into test123_string is not necessarily a valid requirement. I rather kept it simple and separated ABCccc into a_b_cccc instead of ab_cccc because it does not lose information this way and the backward conversion will give the exact same string we started with. Even if you want to do it the other way it is relative easy to write a regex for it with positive lookbehind (? or two regexes without lookbehind if you are not a regex expert. There is no need to split it up into substrings not to mention deciding between strtolower and lcfirst where using just strtolower would be completely fine.