Question

I’m not totally sure but this looks wrong:

I have a header file named fraction.h in which I store a fraction structure and the methods to handle it, one method is used to write a fraction in a file and in the signature of this function one argument is a FILE pointer.

fraction.h:

...
const Fraction * fraction_fwrite(const Fraction * f, FILE * file);
...

fraction.c:

#include <stdio.h>
#include "fraction.h"
...

Now when I try to compile a program that uses a fraction, I get an error,

here is what I have in my Makefile:

program_test: fraction.o program_test.o

and I include fraction.h in program_test.c of course.
but I keep getting this error :

fraction.h:34:54: error: unknown type name ‘FILE’

someone could explain the different steps through which the compiler includes files ?
because <stdio.h> is in fraction.c so why does it strike this unfound-type error ?

should I include <stdio.h> in fraction.h ? which looks not really appropriate from my measly experience.

Answer 1

When you compile program_test, the compiler isn’t looking at the other .c files, only the files you #include in the file you actually compile.

So, you either have to #include <stdio.h> in the test program, just like in fraction.c, or include it in the header file.

Even though the C standard says that the standard library files will not include each other, there is nothing saying that user defined files cannot do that. In fact it is usually much easier to use them if they do.