Why doesn't the compiler give a conflicting error?

Question

In following code, I have declared a structure member variable as a same name of structure name.

struct st 
{     
    int st;
};

int main()
{
   struct st t;
   t.st = 7;
   return 0;
}

I wonder, it's working fine on GCC compiler and doesn't give a conflict error.

So,

• How does the compiler know structure name and variable name?
• What mechanism compiler internally use?

Answer 1

Yes, it's valid. The struct tag and the struct members are in different namespace.

C11, 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 the member via the . or -> operator);
• all other identifiers, called ordinary identifiers (declared in ordinary declarators or as enumeration constants).