| C_CrossHairInfo | Structure to hold cross hair information |
| CALL_DATA | Union of message, io event and integer sample and integer event |
| CALLD_DATA | Union of message, io event and double sample and double event. The DEVENT2 (fe2) and DSAMPLE2 (fs2) members contain additional data for the EyeLink 3. This defaults to 0 or MISSING if used with a preceding model of camera |
| CALLF_DATA | Union of message, io event and float sample and float event. The FEVENT2 (fe2) and FSAMPLE2 (fs2) members contain additional data for the EyeLink 3. This defaults to 0 or MISSING if used with a preceding model of camera |
| CDEVENT | Floating-point eye event with floating point time |
| CDEVENT2 | Floating-point eye event with floating point time |
| CDIOEVENT | Button, input, other simple events with floating point time |
| CDISPLAYINFO | This structure holds information on the display |
| CDMESSAGE | Like IMESSAGE but with floating point time |
| CDSAMPLE | Floating-point sample with floating point time |
| CDSAMPLE2 | Floating-point sample with floating point time |
| CELINKNODE | Name and address for connection |
| CEYEBITMAP | Represents a bitmap image |
| CEYECOLOR | Represents an RGB color |
| CEYEPALETTE | Represents a palette index |
| CEYEPIXELFORMAT | Represents pixel format of an image or surface |
| CFEVENT | Floating-point eye event |
| CFEVENT2 | Floating-point eye event |
| CFSAMPLE | Floating-point sample |
| CFSAMPLE2 | Floating-point sample |
| CGAZE_MOTION | Gaze motion attributes velocity, acceleration for gaze, eye-in-head, head-in-space. Contains data specific to the EyeLink 3 that defaults to MISSING with preceding camera models |
| CHOOKFCNS | Structure used set and get callback functions |
| CHOOKFCNS2 | Extended structure used set and get callback functions |
| CILINKDATA | Class to represent tracker status |
| CIMESSAGE | Message events: usually text but may contain binary data |
| CInputEvent | Union of all input types |
| CIOEVENT | Button, input, other simple events |
| CKeyInput | Keyboard input event structure |
| CMICRO | |
| CMouseButtonEvent | Mouse button event structure (For future) |
| CMouseMotionEvent | Mouse motion event structure (For future) |
