c - dereferencing pointer to incomplete type

Question

I've seen a lot of questions on this but I'm going to ask the question differently without specific code. Is there a way of EASILY determining what is causing the type to be incomplete? In my case I'm using someone elses code and I'm completely sure I don't have the headers right, but (since computers do this stuff much faster and better than human eyeballs) is there a way to get the compiler to say, "hey you think you have type X at line 34 but that's actually missing." The error itself only shows up when you assign, which isn't very helpful.

Answer 1

I saw a question the other day where someone inadvertently used an incomplete type by specifying something like

struct a {
    int q; 
}; 
struct A *x; 
x->q = 3;

The compiler knew that struct A was a struct, despite A being totally undefined, by virtue of the struct keyword.

That was in C++, where such usage of struct is atypical (and, it turns out, can lead to foot-shooting). In C if you do

typedef struct a {
    ...
} a;

then you can use a as the typename and omit the struct later. This will lead the compiler to give you an undefined identifier error later, rather than incomplete type, if you mistype the name or forget a header.