Thread: sending a struct to a function

Hi Guys,

I have the following code that is working fine and I was wondering what is the preffered way to send an array of struct to a function, and if I should make any changes to make this code look more proffestional.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>


typedef struct
{
  int day,month,year;
} Date;


typedef struct
{
  Date date;
  int hh,mm;
  char description[100];

} Meetings;


void ShowMenu()
{
  system("CLS");
  puts("a. Add");
  puts("d. Delete");
  puts("u. Update");
  puts("s. Show All");
  puts("x. Exit");
}

void AddMeeting(Meetings *m)
{
  puts("Date:");
  scanf("%d/%d/%d",&m->date.day, &m->date.month, &m->date.year);
  puts("Hour:");
  scanf("%d:%d",&m->hh, &m->mm);
  flushall();
  puts("Description:");
  gets(m->description);
}

Meetings *AllocateMemory(Meetings *m, int *iTotal)
{
  ++(*iTotal);
  m=realloc(m,(*iTotal)*sizeof(*m));
  if (m==NULL)
  {
	puts("Not enough memory!");
	exit(1);
  }
  return m;
}

int main(void)
{
  Meetings *meetings=NULL;  
  int iTotal=0;
  char ch;
  
  do
  {
    ShowMenu();
	ch=getch();

	switch(ch)
	{
	  case 'a':
		meetings=AllocateMemory(meetings,&iTotal);
		AddMeeting(&meetings[iTotal-1]);
	  break;
	}

  } while (ch!='x');

  if (meetings!=NULL)
	free(meetings);

  return 0;
}

Many Thanks!!!

Excellent words DWK!

I have one more question.
Which one of the following is the best way to pass the first element of the struct to a function?

Code:

1. AddMeeting(&meetings[0]);
2. AddMeeting(meetings);
3. AddMeeting(&meetings);

Thanks Again!

Thank you again DWK!
Good spelling and programming lesson!

Originally Posted by salvadoravi

Excellent words DWK!

I have one more question.
Which one of the following is the best way to pass the first element of the struct to a function?

Code:

1. AddMeeting(&meetings[0]);
2. AddMeeting(meetings);
3. AddMeeting(&meetings);

Thanks Again!

The third is not equivalent to the first two. Of the first two, I would usually use the second. (If I saw the first in code, I would either think that (a) the person didn't know that meetings == &meetings[0], or (b) the person is explicitly stating that s/he only intends to deal with the first element of the array, depending on how competent the rest of the code looks and the comments nearby.) If you intend your function to process the whole array, you should certainly use form #2. I would only use form #1 if I really wanted to emphasize that I was only looking at element #0, or for parallelism with something like AddMeeting(&meetings[iTotal-1]) where the address-of-element format is clearly best.

Either way, if your comments tell (accurately!) what's going on, I don't think anyone will care much about 1 vs. 2.

Originally Posted by tabstop

If you intend your function to process the whole array, you should certainly use form #2. I would only use form #1 if I really wanted to emphasize that I was only looking at element #0, or for parallelism with something like AddMeeting(&meetings[iTotal-1]) where the address-of-element format is clearly best.

What will be the preffered way:

Code:

1. AddMeeting(&meetings[iTotal-1]) 
2. AddMeeting(&meetings+iTotal-1)

Originally Posted by dwks

Oh, you're welcome.
Excellent use of sizeof(*m), by the way. But you have to obfuscate it!

Code:

*iTotal*sizeof*m

Just kidding.

I don't understand should I change sizeof(*m) to sizeof*m ??

Thanks again

Originally Posted by salvadoravi

What will be the preffered way:

Code:

1. AddMeeting(&meetings[iTotal-1]) 
2. AddMeeting(&meetings+iTotal-1)

Number 2 would have to be AddMeeting(meetings+iTotal-1); remember that meetings by itself is already a pointer, so &meetings is a pointer to a pointer and then it all gets weird.

As to which is preferred: anyone who voluntarily uses #2 over #1 should be shot. (Well, maybe not really.)

Originally Posted by salvadoravi

I don't understand should I change sizeof(*m) to sizeof*m ??

Thanks again

No. Obfuscated can be interesting when you're in the mood for it, but for actual real code with actual real programs, no.

Originally Posted by matsp

That depends on how old the compiler / C runtime is. Many older compilers will not "ignore NULL" when called for free, which of course will mess up the entire memory allocation ever after. That said, it is a fair argument that if this doesn't work right, it's a good reason to consider ther compiler "ancient and in need of replacement with something new", just like a car with 500000 miles on the clock wouldn't be a good thing.

--
Mats

What is your recommendation?
Should I use

Code:

if (meetings!=NULL)
   free(meetings);

For portability?

Or should I assume that anyone have new compiler?