直接访问结构中的联合

Question

Let's say I have the following tagged union:

typedef struct Form {
    FormType type;
    union {
        TaxForm tax; 
        BusinessForm bus; 
    } u;
} Form;

To access the main/sub object I have to do:

form->u.bus

Is there a way to either do:

form->u

Or:

form->bus

That is, to be able to access union object directly without going through its declarator (since by definition, the union will only have one item set).

Answer 1

You can only do this by omitting the u from the original definition:

typedef struct Form {
    FormType type;
    union {
        TaxForm tax; 
        BusinessForm bus; 
    };  // <--- no u
} Form;

Then you can use form->bus and so on, where form is a pointer to Form .

This is called "anonymous unions" and was added in the C11 standard revision, so you will need to invoke your compiler in C11 or later mode, or hope that it supported this as an extension in older modes.