array type has incomplete element type

Dear colleagues,
One of my friend have a problem with c code. While compiling a c program it displays a message like
"array type has incomplete element type". Any body can provide a solution for it.
Jaganadh.G

If I have the following code

struct foo;
struct bar
{
    struct foo a_foo;
};

this will fail to compile because the complete size of foo is not known prior to the definition of struct bar.

You need to identify the type that is preventing the compilation and ensure it is defined before it's use.