Here are the data structures with brief descriptions:

Cclock_DateTime	Represents date & time values for display
Cgamepad_State	Represents current input state of a gamepad
CIODIRENT	Directory entry detailing information about a file or directory
CMat4	A 4x4 matrix
CQuaternion	A quaternion
Csound_emitter	Struct containing the state of a sound emitter
Csound_sample	Represents a loaded sound sample
Cvdp_Color32	A 32-bit color
Cvdp_Rect	An axis-aligned rectangle
Cvdp_Vertex	A vertex which can be passed to vdp_drawGeometry
CVec2	A two-component vector
CVec3	A three-component vector
CVec4	A four-component vector