Function cnlp_solve 

pub unsafe extern "C" fn cnlp_solve(
    problem: CNLP_ProblemPtr,
    user_da: CNLP_UserDataPtr,
) -> CNLP_SolveResult

Function calling the Ipopt optimization algorithm for a problem previously defined with cnlp_create_problem. The return specified outcome of the optimization procedure (e.g., success, failure etc).