Thread: Passing different object pointer types to the same arg?

Hello quzah,

Thankyou for your response. One thing though, in your sample, if t = 1, I will do something... with... struct1, then another time if t = 2, I will do something else ...with struct2. So like this:

Code:

#include <stdio.h>

typedef struct tag1{
int a;
long h;
}t1;

typedef struct tag2{
int a;
int *y;
}t2;

void f1(void *i, int s)
{
    if(s == 1)
     {
        t1 *X = (t1*)i;	
        X->a = 9;
      }
    else if(s==2)
      {
         t2 *Y = (t2*)i;
         Y->a = 11;
      }
}

int main()
{
t1 x;
t2 y;

f1(&x,1);
f1(&y,2);
}

In my project, this so called "something" that we do for struct1 is also done identically for struct2 and can be 30 or 40 lines long! Also, to remind ourselves that t can be 1 to perhaps 50 or 100.... therefore, f1() will be very long with alot of if's/else statements containing the the same 50 or 100 lines. Here let me show a sample function in my real code:

Code:

void DDLB_retrieve_from_eeprom(                        
ddlb    *obj_ddlb,  enum eSPI_MEMBANK  Eep_Bank_Num,  		
unsigned short eeprom_gsoa)    	
{
unsigned char   j, k, s, totLists;  
unsigned char   eeprom_buff[4096];
unsigned char   eep_Val1 = 0, eep_Val2 = 0;

totLists 	=  obj_ddlb->dc_size;
ULC_FLASH_SPI_high_speed_read(eeprom_buff, Eep_Bank_Num, 0, 0, 4096);

eep_Val1 = eeprom_buff[eeprom_gsoa];
eep_Val2 = eeprom_buff[++eeprom_gsoa];
obj_ddlb->gso_address = API_combine_chars_to_short(eep_Val1, eep_Val2);  

for(j=0; j<totLists; j++)
{      
  eep_Val1 = eeprom_buff[++eeprom_gsoa];			
  eep_Val2 = eeprom_buff[++eeprom_gsoa];
  obj_ddlb->F__choice[j] = API_combine_chars_to_short(eep_Val1, eep_Val2);  

  eep_Val1 = eeprom_buff[++eeprom_gsoa];			
  eep_Val2 = eeprom_buff[++eeprom_gsoa];
obj_ddlb->F__list_lenght[j] = API_combine_chars_to_short(eep_Val1, eep_Val2);  
}

for(j=0; j<totLists; j++)
 {
  k = (gsoDdlbx->F__list_lenght[j]);    
  obj_ddlb->E__ll[j] = malloc(k * sizeof(unsigned short));   // freed elsewhere!
            
  for(s=0; s<k; s++)
  {
    eep_Val1 = eeprom_buff[++eeprom_gsoa];
    eep_Val2 = eeprom_buff[++eeprom_gsoa];
    (obj_ddlb->E__ll[j])[s] = API_combine_chars_to_short(eep_Val1, eep_Val2);  
  }
 }
}

So as you can see, I would like to have the code above written once in my function while being able to cast the first argument to the appropriate type. Right now I always have to pass in a pointer to a ddlb struct. Hence, I have this function written 5 times in my code.... to acomodate 4 other types. Its very sad! In the future I can end up with 50 types as opposed to the 5 types I have now. If I start embeding the above code in 50 "if/else if" statements.............. I don't know about you, but I just don't like it! Theres got to be a better way!

laserlight suggested ... function-style macro instead of a function. I wouldn't know exactly how to do this. If someone can direct me to some samples on the Internet... that would be very appreciated. I looked for this myself, but unfortunately I did not find anything that suited my issue.

Standing by... please do get back.... all help and suggestions are welcome and appreciated! Thanks

Hello laserlight,

I have seen C macros samples in books ...here and there... and on the net.... like this:

Code:

#define SET_LINKS(p) do { \
        (p)->next_task = &init_task; \
        (p)->prev_task = init_task.prev_task; \
        init_task.prev_task->next_task = (p); \
        init_task.prev_task = (p); \
        (p)->p_ysptr = NULL; \
        if (((p)->p_osptr = (p)->p_pptr->p_cptr) != NULL) \
                (p)->p_osptr->p_ysptr = p; \
        (p)->p_pptr->p_cptr = p; \
        } while (0)

and here:

Introduction to Macros in C | Bukisa.com

But excuse my ignorance, I haven't been programming that long which leads me to say that I don't see how the above #define macro can solve my *original* post in this thread.

I like your proposition... as you said:

>you would be able to write a RETRIEVE_FROM_EEPROM macro that wraps its body >in a do while (0) loop, allowing you to declare the "local" variables that you need.

But I just wouldn't know where to start, confused!

Then, in reference to my innitial post (see below), how would I write the f1() macro that wraps its body in a do while (0) loop, allowing me to declare the "local" variables that I need.....<<<< I never did this before! I would like to learn please.
:-)

If we take my original code sample, based on your #define proposition where would the #define statement go and what would it contain... :

Code:

#include <stdio.h>

typedef struct tag1{
int a;
long h;
}t1;

typedef struct tag2{
int a;
int *y;
}t2;

void f1(void *i)
{
//   t1 *R = (t1*)i;	
//  R->a = 9;

// Can you please provide some code to get me started.... 

}

int main()
{
   t1 x;
   t2 y;
   f1(&x);
   f1(&y);
}

Thanks for your kind help.
Bobby

>It would solve it if all that you are doing right now is to copy and paste the >function verbatim, changing the function name, the type (and possibly the name) >of the obj_ddlb parameter, but with everything else exactly the same.

confused! Help... I need a sample!

Lets use the *original* post: this one:

Code:

#include <stdio.h>

typedef struct tag1{
int a;
long h;
}t1;

typedef struct tag2{
int a;
int *y;
}t2;

void f1(void *i)
{
//   t1 *R = (t1*)i;	
//  R->a = 9;

// Can you please provide some code to get me started.... 

}

int main()
{
   t1 x;
   t2 y;
   f1(&x);
   f1(&y);
}

- So I have to change the function name... so I have to change f1()'s name????
- the type ????
- (and possibly the name) >of the obj_ddlb parameter

I don't get it... I need a small sample... I am completely lost... confused I don't see what you mean.... can someone elaborate on what I should be doing. discouraged!

Code:

typedef struct common {
   int a;
   double foo;
}common;
typedef struct {
   common com;
   int *y;
} t1;

typedef struct {
   common com;
   long int h;
} t2;

void f(void *p)   // pass t1 or t2 pointer
{
   common *cp = p;
   cp->a = 9;
   cp->foo = 3.43;
}
int main(void)
{
   t1 x;
   t2 y;
   f(&x);
   f(&y);
   printf("%d %g\n",x.com.a,x.com.foo);
   printf("%d  %g\n",y.com.a,y.com.foo);
   return 0;
}

Put all common members in struct and make it the first member.

Thanks Bayint Naung!

1) Is it obligatory to make it the first member?
2) Is it possible to do all of this without using an extra common structure? Perhaps by a #define macro or something like that... just asking!

Thankyou for listening to my "I need a small sample" plead.

I appreciate your straight forwards help!

Regards
Bobby

I don't know how you could access the common struct if it's put further down.
since offsetof() needs struct type.
Having common struct as first member is definitely easier.
1) Is it obligatory to make it the first member?
Yes, because standard grantees that there'll be no padding in front of first member.
i.e

Code:

    t1 x;
    t2 y;
    &x == &(x.com) 
    &y == &(y.com)

2) Is it possible to do all of this without using an extra common structure? Perhaps by a #define macro or something like that... just asking!
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