Overloading with struct in C - c

Question

I am trying to write a function with the same name, but that accepts 3 different typers of structs.I don't know how I can write the parameters to do this.So in the _______, there should be proffesore, amminustratore, studente. Sp that the function can accept all 3 types of struct but only one at the time.
Here is the code:
int confermaCredenziali(struct ______ dati, char *uN, char *pW);
struct amministratore{
char userName[MAX_LNG];
char passWord[MAX_LNG];
int stato;
struct ammin *next;
};
struct professore{
int ID;
char userName[MAX_LNG];
char passWord[MAX_LNG];
int stato;
struct prof *next;
};
struct studente{
int ID;
char *userName[MAX_LNG];
char *passWord[MAX_LNG];
int punti;
int stato;
struct studente *next;
};
int confermaCredenziali(struct ______ dati, char *uN, char *pW){
while (dati != NULL) {
if (strcmp(dati->userName, uN) == 0 && strcmp(dati->passWord, pW) == 0){
if (dati->stato == 1)
return 1;
else{
printf("Il suo stato e' passivo.\n");
return 0;
}
}
dati = dati->next;
}
printf("Credeziali errate.\n");
return 0;
}

Answer 1

I suggest a single struct type like this
typedef struct person {
char userName[MAX_LNG];
char passWord[MAX_LNG];
int stato;
struct person *next;
} person_t;
Then you have three linked lists
person_t *amministratore = NULL;
person_t *professore = NULL;
person_t *studente = NULL;
Also, the function needs a pointer argument, I suggest
int confermaCredenziali(person_t *dati, char *uN, char *pW)
Then you pass the head of the linked list you have selected, to the function. It works with one list at a time, and the three lists are completely separate.

Answer 2

As stated earlier in comments:
Create as follows:
Include all three struct as members of a union.
add the union as a member of a collector struct.
Add an additional enum member to the collector struct to identify which of the three struct you are passing.
The following illustrates:
typdef enum {
ADMIN,
PROF,
STUD,
MAX_S
}S_TYPE;
typedef struct {
...
}amministratore;
typedef struct {
...
}professore;
typedef struct {
...
}studente;
typedef union{
administratore admin;
professore prof;
studente stud;
}s_union;
typedef struct {
s_union;
S_TYPE type;
}collector;
Your prototype would be modified to:
int confermaCredenziali(collector *c, S_Type type, dati, char *uN, char *pW);
As mentioned also in comments, the argument for this struct as passed in the prototype should be as pointer, so that the members can be changed, and for efficiency, as a pointer is often times smaller than the entire struct

Answer 3

this example is trivial but you can do something like this:
enum type{STUD = 0, PROF, ADMIN};
int confermaCredenzialiSTUD(void *dati, char *uN, char *pW);
int confermaCredenzialiPROF(void *dati, char *uN, char *pW);
int confermaCredenzialiADMIN(void *dati, char *uN, char *pW);
const int (*credenziali[3])(void *, char *, char *) =
{confermaCredenzialiSTUD, confermaCredenzialiPROF, confermaCredenzialiADMIN};
int confermaCredenziali(enum type t, void *dati, char *uN, char *pW)
{
return redenziali[t](dati, uN, pW);
}
and in the functions do correctly what you need for the particular type.