Check Unix password in PHP

Hi all, I am trying to check password that user typed with the one in Unix system. Some tutorial(or PHP Manual) just retrieves content in /etc/passwd and compare it, but password could be stored in shadow, not in passwd; someone suggested to write a tiny C code, chown it to root, change sticky bit and run it in PHP; someone used ypcat to compare it...... Personally I prefer to write a tiny C code, I just wonder if it is safe? Is there any "Standard & Safe" way to do this job ? Thanks in advance, Siman