How to define functions from declarations where the parameters do not have identifiers?

Question

For an assignment, I was given a header file. The objective was to write the function definitions in a C file.

I am confused about how to write the definition for the functions when some of them do not have identifier names.

#include <stdint.h>

/** Course subjects. */
enum subject {

    SUBJ_ENGI,
    SUBJ_CIV,
    SUBJ_ECE,
    SUBJ_MECH,
    SUBJ_ONAE,
    SUBJ_PROC,
    SUBJ_CHEM,
    SUBJ_ENGL,
    SUBJ_MATH,
    SUBJ_PHYS,
};

struct course;

// Define the following functions:

struct course*  course_create(enum subject, uint16_t code);

enum subject    course_subject(const struct course*);

uint16_t    course_code(const struct course*);

void        course_hold(struct course*);

void        course_release(struct course*);

int     course_refcount(const struct course*);

I am not sure how I am supposed to define these functions when the prototypes do not have identifier names. For example, wouldn't it make more sense for the parameter to be const struct course* <Identifier> instead of just const struct course* ?

Answer 1

Parameter names are not needed in declarations because C matches arguments to parameters by position, not by name. Parameter names are needed inside a function definition so the body of the function has a way to refer to the function.

Define the functions using any parameter names you want. Simply repeat the declaration, insert whatever you want for the missing names, and replace the ; that terminates the declaration by a {…} compound statement that defines the function.

Answer 2

Declarations are not definitions, the following code in the header file are declarations:

struct course;
enum subject    course_subject(const struct course*);

You don't need to have parameter name in declarations, you need them in definitions. eg in implementation.c file, you could have:

struct course {
    // add your fields
};

enum subject  course_subject(const struct course* c)
{
    // access c's fields
}

in this case you will have to provide a name for the course parameter so that you can refer to it.