Nested typedef structs

Question

I'm having an issue trying to nest structs that I need to declare as new var types. The code is the following-

typedef struct
{
    typedef struct
    {
        int day,
            month,
            year;
    } Date;

    Date manuDate,
         purDate;
    double purPrice;
} Car;

Except when I try to compile it throws an error at me saying

"Syntax error before typedef" and a bunch of other errors due to that further down.

Is this something C cannot do? I know it has issues with nested structs without having a pointer but I'm not sure how that would work in this case...

Answer 1

C does not support nested structure definitions. Perhaps you were looking at some C++ code.

Instead, you simply define the "inner" struct first, and then reference it within the "outer" struct.

typedef struct
{
    int day,
        month,
        year;
} Date;


typedef struct
{
    Date manuDate,
         purDate;
    double purPrice;
} Car;

Answer 2

C does have nested structs/unions/enums but not nested typedefs.

struct A { typedef struct B { int x; } B; }; //WRONG
struct A { struct { int x; } b; }; //OK - an anonymous nested struct w/ an instance
struct A { struct { int x; }; }; //OK - an anonymous nested struct w/out an instance; x effectively belongs to `struct A`
struct A { struct B { int x; } b; }; //OK, the `struct B` type also becomes available in the outer scope
struct A { struct B { int x; }; }; //WRONG, an tagged nested struct needs at least 1 instance

The nested structs/unions/enums can either be anonymous (untagged) in which case they become part of the outer struct/union or tagged.

An anonymous inner struct/union can also get away without defining instances, in which case the inner members become members of the outer struct/union recursively.

A tagged nested struct/union/enum needs instances and it's like an anonymous nested struct/union/enum with instances except the tagged type also becomes available for later use, behaving as if it were a standalone outer-scope struct/union/enum definition.

It might be wise to simply put a tagged struct/union/enum in the outer scope rather than confusingly nest it inside another struct/union.