Suggestion about managing users and password

[ZaC]

Hello evrybody!
I'm coding a server in C in wich a client could autenticate himself or not.
Username and password are sotred in a binary file with a fixed format (16 bytes for the user name, 16 bytes for the password).
What is the best way to manage the autentication?
A- to load the U&P file in a sorted array of structure usrNpsw_t and than to implement a binary search.
B- to search in the binary file the username evrytime someone try to autenticate?
C- something else i didn't think
Thanks for any kind of suggestion
ZaC

PS: sorry for my bad english. I hope my trouble is clear

[MacGyver]

This is one of those things that depend upon several factors.

If authing will happen often, and if the user list is short, store the entire thing in memory in some sort of smart data structure (ie. hashing sounds good for a lookup) and go from there.

[ZaC]

thank you, MacGyver