I have a struct that declared as follow:
struct a {
struct b {
int d;
} c;
};
How to declare a variable of b outside a? In C++ I can use a::b x;. But, in C it required to specifies struct keyword before struct name.
2 Answers
C has a flat layout; when you declare a struct within another struct, the former is just being put into the global namespace.
So, in your example, it is just struct b.
3 Comments
david.pfx
Where does the standard say that?
keltar
@david.pfx not sure, but 6.2.1
If the declarator or type specifier that declares the identifier appears outside of any block or list of parameters, the identifier has file scopedavid.pfx
@keltar: Actually, no. I think it might be 6.2.3 Name spaces and note 32, which make it clear there is only one namespace for tags, but a separate namespace for members of each struct or union.
C does not have nested types. You can't write a::x b or anything that ressembles it. If you want to get rid of the struct keyword, that's another problem. Use typedefs. but it won't allow to nest types.
typedef struct b_t {
int d;
} b;
typedef struct {
b c;
} a;
b some_b;
a some_a;
int f() {
some_b.d=42;
some_a.c=some_b;
return 0;
}
.
