Initializing function in LL

Question

If I have the following structure defined:

typedef struct bear_t { 
    char* name;
    void (*eat)(struct bear_t* this); 
    void (*drink)(struct bear_t* this); 
    void (*sleep)(struct bear_t* this); 
    void (*study)(struct bear_t* this); 
    void (*live)(struct bear_t* this); 
    void (*dtor)(struct bear_t* this); 
    int health;
    int happiness; 
} bear_t;

In a bear_t* create_bear(void) method, I want to do the following:

• Create a new bear with malloc
• Initializes the bear’s eat, drink, sleep, and live functions to the default values (eat_fish, drink_water, sleep_lots, live).
• Initializes the study function to NULL, since default bears don’t know how to study.
• Initializes the bear’s health and happiness to 0.
• Initializes the bear’s destructor (dtor) field to delete_bear.
• Sets the bear’s name to “bear” (bear->name=”bear” is sufficient).
• Returns the bear to the caller.

How would I initialize the functions?

Answer 1

There is nothing particularly complicated about initializing function pointers:

void eat_fish(struct bear_t* this)
{
    this->happiness += 42;
    this->health += 23;
}
void drink_water(struct bear_t* this)
{
    this->happiness += 10;
    this->health += 12;
}
// ....

bear_t* create_bear(void)
{
    bear_t *bear = (bear_t*)malloc(sizeof(bear_t));
    bear->name = "bear";
    bear->eat = &eat_fish;
    bear->drink = &drink_water;
    bear->sleep = &sleep_lots;
    bear->live = &live;
    bear->study = NULL;
    bear->dtor = &delete_bear;
    bear->health = 0;
    bear->happiness = 0;
    return bear;
}

As a side note, please not that this kind of Object-Oriented coding in plain C-style is really not a simple way to do things. If you're actually trying to get into C++ (as the tags to the question would suggest), try sticking to the "ordinary" way of doing these kinds of things, which would be using (virtual) member functions.