business function to detect file extension position

is there a business function to detect the file extension character. Below are my use cases

If I have the path below

\\servername.abc.com\cars\make\cars.txt

then it will return position 37 for the period character before the TXT. 

If I have no file extension like below

\\servername.abc.com\cars\make\cars

Then it will return 0 since there's no file extension