It should make it a lot easier to understand this tutorial is you are familiar with the data types involved in keyboard access, so I'll explain them first.
SDLKey is an enumerated type defined in SDL/include/SDL_keysym.h and detailed here. Each SDLKey symbol represents a key, SDLK_a corresponds to the 'a' key on a keyboard, SDLK_SPACE corresponds to the space bar, and so on.
SDLMod is an enumerated type, similar to SDLKey, however it enumerates keyboard modifiers (Control, Alt, Shift). The full list of modifier symbols is here. SDLMod values can be AND'd together to represent several modifiers.
typedef struct{
Uint8 scancode;
SDLKey sym;
SDLMod mod;
Uint16 unicode;
} SDL_keysym;The SDL_keysym structure describes a key press or a key release. The scancode field is hardware specific and should be ignored unless you know what your doing. The sym field is the SDLKey value of the key being pressed or released. The mod field describes the state of the keyboard modifiers at the time the key press or release occurred. So a value of KMOD_NUM | KMOD_CAPS |