Typedef

typedef lets you create a shorthand alias for an existing type. This is particularly useful for making your code more readable and reducing repetitive typing – especially when working with structs, enums, or complex types.

Basic Syntax

typedef existing_type new_name;

For example, instead of writing unsigned long int everywhere, you can create a shorter alias:

typedef unsigned long int ulong;

ulong my_variable = 100;  // Much easier to read!

Typedef with Structs

Without typedef, you have to write struct every time you use your struct:

struct Point2D {
  int x;
  int y;
};

struct Point2D origin = { 0, 0 };  // Note the 'struct' keyword
struct Point2D dest = { 10, 20 };

With typedef, you can skip the struct keyword:

typedef struct {
  int x;
  int y;
} Point2D;

Point2D origin = { 0, 0 };  // Much cleaner!
Point2D dest = { 10, 20 };

Typedef with Enums

Similarly, typedef makes enums cleaner:

// Without typedef
enum Direction { UP, DOWN, LEFT, RIGHT };
enum Direction player_dir = UP;

// With typedef
typedef enum { UP, DOWN, LEFT, RIGHT } Direction;
Direction player_dir = UP;  // Cleaner!

Common Uses

typedef is commonly used for:

Structs and enums – reduces repetition
Function pointers – makes complex function pointer syntax more readable
Platform-specific types – e.g., uint8_t, size_t are often typedefs

Tips

Use typedef to make your code more readable, not to obscure what’s happening
Don’t overuse it – sometimes writing struct MyStruct makes it clearer that you’re dealing with a struct
Convention: Many programmers suffix typedef’d struct names with _t (e.g., point_t) to indicate it’s a typedef. We do this in the Unit 3 & 4 libraries, but this isn’t required