Sending Pointers of Structs to a Function in C - c

Question

I don't love this, but I have a struct with nearly 45 members inside; all are characters or character arrays. That said, I am going to need to optimize the way I initialize each struct. Ordinarily, I would pass the entire object into my init_struct() function, but I feel like that is not the best way to do this.
How would I create and use a pointer to the struct to accomplish this?
Old Method would look something like this:
void init_struct(struct general){
...initialize members...
}
int main(){
struct general[10];
for(int i = 0 ; i < 10 ; ++i){
init_struct(general[i];
}
}
Since this struct is so large, as I said nearly 45 members inside it, I think a point to the struct would go a long way in optimizing this process. How would I accomplish that?
Just in case you need, here is the typedef for my struct
typedef struct
{
//Basically, everything we want to read from HUDL should be here...
int play_num;
char down;
char dist[3];
char ydln[4];
char gnls[3];
char hash[3];
char home[20];
char away[20];
char odk[2];
char qtr[2];
char series[3];
char result[20];
char penalty[20];
char act_cb[20]; //How do they act post-snap
char act_dl[20];
char act_lb[20];
char act_ol[20];
char act_qb[20];
char act_rb[20];
char act_saf[20];
char aln_cb[20]; //How do they align pre-snap
char aln_dl[20];
char aln_lb[20];
char aln_ol[20];
char aln_qb[20];
char aln_rb[20];
char aln_saf[20];
char aln_wr[20];
char blitz[20];
char box_cnt[3];
char saf_count[20];
char coverage[20];
char cvr_basic[20];
char def_front[20];
char mtn_def[20];
char num_rush[3];
char off_form[20];
char form_var[20];
char motion[20];
char off_pro[20];
char off_play[20];
char play_var[20];
char personnel[20];
char play_type[20];
char time[2];
char score_diff[4];
char field_zone[2];
char dd_type[2];
char form_strength[2];
} HUDL; // MAXIMUM of 63 Members

Answer 1

There's a couple of things wrong on your code.
First of, your function definition is wrong because you omit the parameter name. Your function definition should look like this:
void init_struct(struct general mygeneralstruct){}
Alternatively, you could use an alias for your struct using typedef, like so:
typedef struct {
int a;
} general;
In which case, your function declaration could look like this:
void init_struct(general mygeneralstruct){}
You have the same problem when you declare your array of structures. You omit the name of your variable. Instead of
struct general[10];
it should be
struct general mygeneralstruct[10]
or
general mygeneralstruct[10](typedef)
Finally, you can't change your array of structures by passing each structure's value to the function. You need to pass each structure's address instead.
Your function declaration should then be(using typedef):
void init_struct(general* mygeneralstruct){}
and the code in the loop:
init_struct(&mygeneralstruct[i]);

Answer 2

To pass a pointer to your array element, you just prefix the parameter with &, make sure you declare the function correctly:
void init_struct(HUDL* pGeneral){
if ( pGeneral != NULL ) {
//This will ensure the entire structure contains '0'
memset(pGeneral, 0, sizeof(HUDL));
...initialize members...
}
}
int main(){
HUDL general[10];
for( int i=0; i<(sizeof(general) / sizeof(general[0])); i++ ) {
init_struct(&general[i]);
}
}
I'm not sure why you haven't used the typedef 'HUDL' makes life a lost easier and code easier to read.

Answer 3

A slightly cleaner and better approach would be to have a constructor and destructor function to allocate memory dynamically to structure and free it after use.
static void HUDL_destroy(HUDL* ptr)
{
if(ptr)
{
//...any other clean up that needs to be done goes here..
free(ptr);
}
}
static HUDL* HUDL_create()
{
HUDL* ptr = malloc(sizeof(HUDL));
if(!ptr)
return NULL;
//do initialization bits...
init_struct(ptr);
return ptr;
}
int main()
{
//allocate and initialise structure
HUDL *general = HUDL_create();
//do stuff...
//free structure after use
HUDL_destroy(general);
}
You might need an array of pointers in your case. So modify your main() accordingly.
int main()
{
//we need an array of structure pointers
HUDL* general[SIZE];
//allocate and initialize structure
for(int i=0; i<SIZE; i++)
general[i] = HUDL_create();
//do stuff...
//free structure after use
for(i=0; i<SIZE; i++)
HUDL_destroy( general[i] );
}