Resource reservation is a vital issue for grid-enabled programs to execute smoothly. Instead of using metascheduling solutions to request grid resources statically, we are developing a tiny C++ library to reserve on-demand computing resources based on Globus Toolkit, local schedulers such as Maui, and SQLite database. The interface class is named CReservation in the library. At the time of preparing this paper, the only implementation available is for Maui scheduler. With such implementation classes, one can request, release, and monitor reservations of computing resources dynamically. To verify the simplicity, usability, and stability of current library, we have performed an in-depth case study with a grid enabled hybrid MD/QM (Molecular Dynamics/Quantum Mechanical) multi-scale simulation program. Our test shows that this library provides an easy and effective approach to manage resource reservations from within grid-enabled applications.