Checking for md5 or password_hash

Question

Hi folks,

I have a site that is using old MD5 passwords, but I’m re doing the join form which will store new joiners with the upto date hashing. BUT I need to edit the log in code, so that if user on old use old MD5 verify, but if new use new verifi. My thouhts were to use the string length funtion, as the md5 is different to the new hash default. But I’m just can’t get it to work. I’m using an if else statment, to check, then run. Any help please?