Thread: Dynamic variable types

One approach is to work via a pointer to void. This is the approach that qsort takes. Another approach is to turn the function into a macro instead, but this can be error prone if it is feasible in the first place.

don t know how 'large' the function - no code posted is but if it is like a couple of screens length then you might ask questions about it - If it is large and still only accomplishes one or maybe two tasks then ok maybe it has to be that way, but if it is doing lots of jobs then it probably should be looked at.

A third approach is to write macros that declare and define the functions. This is NOT a technique I recommend (overuse of this type of technique can cause some very curly maintenance problems) and, realistically, you would be better off learning C++ and using templates than using this technique.

But, to illustrate, if you want to create a set of related functions ....

Code:

#define CREATE_FUNCTION(type)  type get_##type() {type x;   /* do general things with x */    return x;}

CREATE_FUNCTION(int)
CREATE_FUNCTION(float)
CREATE_FUNCTION(unsigned)

int main()
{
     float f = get_float();
     int i = get_int();
     unsigned u = get_unsigned();

        /*   do things here */

     return 0;
}

The important things to note are;

1) It is necessary for the macro to create function names that depend on the type, since C does not support function overloading. Hence the token pasting (## operator).

2) The macros can only be invoked at file scope (since they define functions). There should not be semi-colons at the end of the lines.

3) Some more tricks are needed to ensure compliance with the one-definition rule. Either use static functions (to make them local to each compilation unit) or use such macro tricks both for function declarations (aka prototypes in header files) and, in exactly one source file, for the definitions (i.e. implementations of the functions).

Hi,

well i have been playing around with helper functions like you guys suggested. and for small examples it works but for my particular example i don't know how to make it work. so i have a queue(array based) and a want to place in ti numbers and the kick them out. But the numbers can be either 64 or 32 bit integers.

Example:

main.c

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
 
#define   HELPER_TYPE       uint32_t
#define   HELPER_NAME(base) base ## _u32
#include "main-helper.c"
#undef    HELPER_NAME
#undef    HELPER_TYPE
 
#define   HELPER_TYPE       uint64_t
#define   HELPER_NAME(base) base ## _u64
#include "main-helper.c"
#undef    HELPER_NAME
#undef    HELPER_TYPE



void main(){

  long int64[10];
  int int32[10];
  int i f,k;
  long j,l;
  for(i=0;i<10;i++){
    int32[i]=i; 
  }
  for(j=0;j<10;j++){
    int64[j]=j;
  }
  
  QueueCnt_u32 *queue = NULL;
  queue = (QueueCnt_u32 *)emalloc(sizeof(QueueCnt_u32));
  queue->front =0; queue->rear = 0; queue->count = 0; queue->last = 0;
  
  for(i=0;i<10;i++){
	  printf("add:%d\n",int32[i]);
	  add_u32(int32[i],queue);
	  if(i==5){
		  f= checkFront_u32(queue);
		  printf("checkF:%d\n",f);
		  f =checkRear_u32(queue);
		  printf("checkR:%d\n",f);
		  for(k=0;k<=5;k++){
		    f= del_u32(queue);
		    printf("del:%d\n",f);
		}
	  }
  }
  f= checkFront_u32(queue);
  printf("checkF:%d\n",f);
  f =checkRear_u32(queue);
  printf("checkR:%d\n",f);
  for(k=0;k<5;k++){
    f= del_u32(queue);
    printf("del:%d\n",f);
 }
  
  QueueCnt_u64 *queueX = NULL;
  queueX = (QueueCnt_u64 *)emalloc(sizeof(QueueCnt_u64));
  queueX->front =0; queueX->rear = 0; queueX->count = 0; queueX->last = 0;
  
  for(i=0;i<10;i++){
	  printf("add:%ld\n",int64[i]);
	  add_u64(int64[i],queueX);
	  if(i==5){
		  l= checkFront_u64(queueX);
		  printf("checkF:%ld\n",l);
		  l =checkRear_u64(queueX);
		  printf("checkR:%ld\n",f);
		  for(k=0;k<=5;k++){
		    l= del_u64(queueX);
		    printf("del:%ld\n",l);
		}
	  }
  }
  l= checkFront_u64(queueX);
  printf("checkF:%ld\n",l);
  l =checkRear_u64(queueX);
  printf("checkR:%ld\n",l);
  for(k=0;k<5;k++){
    l= del_u64(queueX);
    printf("del:%ld\n",l);
 }
  
  
}

main-helper.c

Code:

#include <stdlib.h>

#define MAXWSIZE 15

typedef struct HELPER_NAME(QueueCnt) {            /* queue */

   HELPER_TYPE q[MAXWSIZE];               /* wheel */
   HELPER_TYPE front, rear, count, last;  /* counters */

}HELPER_NAME(QueueCnt);



HELPER_TYPE HELPER_NAME(addone)  (const HELPER_TYPE i) {
	return ((i+1) % MAXWSIZE);
}

void HELPER_NAME(add)(const HELPER_TYPE a,HELPER_NAME(QueueCnt) *cnt){

	if(cnt->rear>MAXWSIZE){
		printf("QUEUE FULL\n");
		return;
	}
	else{
		cnt->count++;
		cnt->q[cnt->rear]=a;
		cnt->last = cnt->rear;
		cnt->rear = addone(cnt->rear);
	}
}

HELPER_TYPE HELPER_NAME(del)(HELPER_NAME(QueueCnt) *cnt){
	HELPER_TYPE a;
	
	if(cnt->front == cnt->rear){
		printf("QUEUE EMPTY\n");
		return(0);
	}
	else{
		cnt->count--;
		a=cnt->q[cnt->front];
		cnt->front= addone(cnt->front);
	}
	return(a);
}

HELPER_TYPE HELPER_NAME(checkFront)(HELPER_NAME(QueueCnt) *cnt){
	HELPER_TYPE a;
	a=cnt->q[cnt->front];
	return (a);
}

HELPER_TYPE HELPER_NAME(checkRear)(HELPER_NAME(QueueCnt) *cnt){
	HELPER_TYPE a;
	a=cnt->q[cnt->last];
	return (a);
}

Oh yes and the error is :

/tmp/ccPdRHLm.o: In function `add_u32':
deal.c.text+0x91): undefined reference to `addone'
/tmp/ccPdRHLm.o: In function `del_u32':
deal.c.text+0x101): undefined reference to `addone'
/tmp/ccPdRHLm.o: In function `add_u64':
deal.c.text+0x214): undefined reference to `addone'
/tmp/ccPdRHLm.o: In function `del_u64':
deal.c.text+0x29c): undefined reference to `addone'
/tmp/ccPdRHLm.o: In function `main':
deal.c.text+0x35b): undefined reference to `emalloc'
deal.c.text+0x506): undefined reference to `emalloc'
collect2: ld returned 1 exit status