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I have the following struct:

struct type1 {
    struct type2 *node;
    union element {
        struct type3 *e;
        int val;
    };
};

When initialising a pointer *f that points to an instance of type1 and doing something like: f.element->e or even just f.element, I get: 

error: request for member ‘element’ in something not a structure or union

What am I overseeing here?

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7
  • Can you show the declaration of f? Maybe you mean f->element.e? Commented Oct 23, 2012 at 19:36
  • 2
    element is the union tag, not a member name. Try with struct { ... union element { ... } elem; }; and f.elem. Commented Oct 23, 2012 at 19:37
  • 2
    @Darksky Your struct member needs a name to access it. The name is given after the type. struct type1 { ... ; union { ... } element; }; would create a member element with type (untagged) union {...}. Commented Oct 23, 2012 at 19:41
  • 1
    @Darksky: In C 1999 and earlier, adding a name to the end of the union declaration does not just give it a different name than its type. It gives it a name. Without that, it does not have a name; there is no object, no member in the enclosing struct. Without that, it is just a declaration of a type, not of a member. Commented Oct 23, 2012 at 19:58
  • 1
    @DanielFischer: C 2011 introduced anonymous unions and structures, in which case the union does not need a name. Commented Oct 23, 2012 at 19:59

2 Answers 2

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3

element is the name of the union, not the name of a member of type1. You must give union element a name:

struct type1 {
struct type2 *node;
    union element {
        struct type3 *e;
        int val;
    } x;
};

then you can access it as:

struct type1 *f;
f->x.e
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5 Comments

Maybe you should malloc memory for your f?
f must be initialized somehow, yes.
There may be some issue of C versions here. C 2011 introduced anonymous structures and unions, in which case f->e would work with the original declaration. However, if Darksky is using an earlier version of C, then the union declaration must be modified as shown in this answer.
@EricPostpischil Correct, but even then, one wouldn't say: f->element.e
f is already initialised in malloc. This solves it. Thanks.
-1

If f is a pointer, then you may access "element" using f->element, or (*f).element

Update: just saw that "element" is the union name, not a member of the struct. You may try 

union element {
    struct type3 *e;
    int val;
} element;

So the final struct would be like this:

struct type1 {
    struct type2 *node;
    union element {
        struct type3 *e;
        int val;
    } element;
};

And now you can access element members like this, through a type1 *f:

struct type1 *f;

// assign f somewhere

f->element.val;
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4 Comments

Read the question please. That's what I did and that's the error I am getting.
@Darksky No. You did f.element and not f->element acording to your question.
No I did do both. Quoting: f.element->e or even just f.element, I get.
@Darksky f.element->e or f.element is not the same as f->element. f. will always be an error with a pointer *f (but anyway the problem with the union still was there before the edit). Regards

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