Do struct tags, union tags and enum tags have separate namespaces?

user_5958455 0
Viewed 324

schot's answer is a good one. He claimed that

  • Tags (names of structures, unions and enumerations).

I think that the tags for structures, unions and enumerations have different namespaces, so that this code is completely fine:

// In the same scope
struct T {};
union T {};
enum T {};

But inferring from the quotation above, it looks like all tags share the same namespace. Is the answer not clear enough or am I wrong?

name-lookup namespaces c
3 Answers

No.

All the tags share the same namespace. So you are not allowed to have:

struct T {...};
union T {...};
enum T {...};

C11 draft N1570, 6.2.3 Name spaces of identifiers explicitly add s footnote.

32) There is only one name space for tags even though three are possible.

user_12751690

No, they do not have separate namespaces. There is only one namespace for tags. This means 

struct TS{};
union TU{};
int TS, TU;

is valid while 

struct T{};
union T{};

is not. Two declarations of T are in the same namespace.

user_24558880

The answer to your question:

Tag names: all identifiers declared as names of structs, unions and enumerated types. Note that all three kinds of tags share one name space.

Just quoting this from reference guide.

At the point of lookup, the name space of an identifier is determined by the manner in which it is used:

  • identifier that follows the keyword struct, union, or enum is looked up in the tag name space.
user_76402690
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