typedef a struct before it's declared

Question

I\'m not a beginner, I\'m very familiar with the following idiom:

typedef struct Foo_ Foo;// I know typedef struct Foo Foo is fine, I\'m just trying to make          


        

Answer 1

typedef is used to create an alias for a type. But that type doesn't necessarily exist when typedef'ed.

For example,

if you just do:

struct Foo;

and you never define the struct Foo anywhere in the program, then it'll still compile. Compiler would assume it's defined somewhere and continue. Only if you use it without defining the struct, an error will occur.

It's the similar case with typedef as well.