Instructions for OCP formulation in C project

Acados_intreface : C;
Goals: Implementing sqp_rti framework in C environment (Model and OCP constructed by python)

I can’t figure out the meaning of variables used by functions defined in C, such as “x”,“u” in ocp_nlp_out_set(). Are they respectively refer to the target states of x and u in a QP solution problem with a step size of N?

I wonder if there are any problem formulas in the C environment which can be referenced?