What is a forward reference in c ?

Question

I know about the forward declaration of structure but don't know when it should be used or preferrable ? I can't envision the scenario.

Answer 1

Using an identifier (variable) before its declaration results in an error. And to avoid this we just declare it but not define it and is called forward reference.

See the following example where it is necessary to define the forward reference as two structure are having cross reference -

struct foo; // Forward reference 

struct bar
{
   struct foo *f;
};

struct foo
{
   struct bar *b;
};

Answer 2

It is a reference to a variable or function before it is defined to the compiler. The cardinal rule of structured language is that everything must be defined before it can be used. There is rare occasions where this is not possible. It is possible to defined two functions in term of each other, Here one will obey the cardinal rule while other will need a forward declaration of the former in order to know of the former's existence.

Answer 3

given address of variable to others,