From TechEncyclopedia <http://www.techweb.com/encyclopedia>: " (Lightweight Directory Access Protocol) A protocol used to access a directory listing. LDAP support is being implemented in Web browsers and e-mail programs, which can query an LDAP-compliant directory. It is expected that LDAP will provide a common method for searching e-mail addresses on the Internet, eventually leading to a global white pages. LDAP is a sibling protocol to HTTP and FTP and

uses the ldap:// prefix in its URL."

You can use LDAP APIs in your C programs with LDAPSDK.