I want to use dtsearch in my desktop application written in C++ and Gtkmm. Can i have any API or link to the API to do my thing.
If you are talking about dtSearch Desktop, the Windows end-user product, it is not intended or licensed to be used via the API.
The dtSearch Engine for Linux (x32 or x64) on the other hand is a developer product and has C++ and Java APIs; it includes file filters for all popular file types, can search multiple indexes at the same time, each holding over 1 Tbyte. Features natural language as well as complex Boolean searching and regular expression searching. At $2500 for a three-server license (includes one year of technical support) it is probably overkill if you just have a single Desktop application to run, but for heavy duty searching inside a datacentre it's a no brainer. Fully functional evaluation downloads at www.dtsearch.com