Question

What is the difference between following 2 enum declarations in C ?

1. typedef enum colour
{ Red, Blue
};

2. typedef enum colour
{ Red,Blue
}colour; //in your response please refer to this colour as colour2 to avoid confusion

Answer 1

In the simplest case, an enumeration can be declared as

enum color {Red,Blue};

Any references to this must be preceded with the enum keyword. For example:

enum color color_variable1;  // declare color_variable of type 'enum color'
enum color color_variable2;

In order to avoid having to use the enum keyword everywhere, a typedef can be created:

enum color {Red,Blue};
typedef enum color color2;  // declare 'color2' as a typedef for 'enum color'

With typedef, The same variablea can be now declared as

color2 color_variable3;
color2 color_variable4;

FYI, structures in C also follows the similar rules. typedef also makes your code look neater without the C struct(enum) keywords. It can also give logical meanings.

typedef int RADIUS;  // for a circle 
typedef int LENGTH;  // for a square maybe though both are int