Where can I find in PHP source files where is the code of an internal function like is_string()? [closed]

Question

I already downloaded the source, and I think the code of is_string() is somewhere in ext/standard/, but I am not sure.

Answer 1

ext/standard/type.c

You can also find it online:

http://git.php.net/?p=php-src.git&a=search&h=HEAD&st=grep&s=%28is_string%29

Edit to add: You can find different version by replacing the h key with e.g.: h=refs%2Fheads%2FPHP-5.6.31

PHP5 uses fewer macros than PHP7, so it looks more like normal C.