Question

I’ve read in SO about different namespaces in C where the type are defined, e.g. there is a namespace for Structs and Unions and a namespace for typedefs.

Is namespace the exact name for this? How many namespaces exist in C?

Answer 1

see 6.2.3

from http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf

6.2.3 Name spaces of identifiers

If more than one declaration of a particular identifier is visible at
any point in a translation unit, the syntactic context disambiguates uses
that refer   to different entities.

 Thus, there are separate name spaces for various categories of identifiers,
as follows:
— label names (disambiguated by the syntax of the label declaration and use);

— the tags of structures, unions, and enumerations (disambiguated by 
 following any32) of the keywords struct, union, or enum);

— the members of structures or unions; each structure or union has a 
separate name space for its members (disambiguated by the type of the 
expression used to access themember via the . or -> operator);

— all other identifiers, called ordinary identifiers (declared in ordinary 
  declarators or as enumeration constants).