Question

I have the following code:

typedef struct Y {int X;} X;
enum E {X};

which generates a error:

error: ‘X’ redeclared as different kind of symbol

As I know, C has implicitly defined namespaces for structure, union, and enum tags and also for their members. So, I’m not sure why does E::X collide with typedef structure tag X?

What exactly are name spaces in C?

Answer 1

C does not have a separate namespace for enum members. When you write enum {X}, that creates a global constant X (which can clash with other global names such as typedef‘d tags).