What exactly is the FILE keyword in C?

Question

I\'ve started learning some C as a hobby and have blindly used FILE as a declaration for file pointers for quite some time, and I\'ve been wondering. Is this a keyword or sp

Answer 1

FILE is an identifier used as a typedef name, usually for a struct. The stdio library usually has something like

typedef struct {
   ...
} FILE;

somewhere. All stdio functions dealing with FILE pointers know the contens of ... and can access the structure members. The C programmers must use functions like fopen, feof, ferror, ungetc etc to create and operate on FILE structures. Such types are called opaque (i.e. you can´t peek inside them but must use accessor functions).

Why is it defined as a pointer?

It isn't. It's a struct to which your code declares a pointer. Note the asterisk in your

FILE* fp;

which is another example of why the asterisk should go with the variable identifier, not the type name:

FILE *fp;