Thread: Deleting an element from an array

Does anyone know a more elegant way than this of deleting a given element from an array:

Code:

void deletefrom(int[], int, int);

int main(void)
{
    /*stuff*/
   int bob, size_of_frank;
   int *frank;
   frank=(int*)calloc(size_of_frank,sizeof(int));

   /*call for element "bob" to be deleted from array "frank"*/
   deletefrom(frank,bob,size_of_frank);

   /*etc*/

   return 0;
}

void deletefrom(int frank[], int bob, int size_of_frank)
{
   int i, j=0, *temp;
   temp=(int*)calloc(size_of_frank-1,sizeof(int));

   for(i=0; i<size_of_frank, i++){
      if(frank[i]==bob)
         continue;              /*Or should this be break?*/
      else{
         temp[j]=frank[i];
         j++
      }
   }

   free(frank);
   frank=(int*)calloc(size_of_frank-1,sizeof(int));
   for(i=0;i<size_of_frank-1;i++)
      frank[i]=temp[i];

   return;
}

But something about this gives me the creeps and that is "Once I have free'd frank, is he gone from main forever? Can main see the new frank?"

Help is much appreciated, even if it turns out to be the thread where you explained this to someone else last week (I did look! But I couldn't find anything on the first five pages...)

Matt

deletefrom() should call reallocate(), not calloc.
You can do all of deletefrom() something like this:

Code:

void deletefrom(int frank[], int bob, int size_of_frank)
{
   /* this truncates the array at the value just before bob */
   int i=0, 
       found=0;
   for(i=0; i<size_of_frank; i++){
      if(frank[i]==bob){
         found=i+1;
         break;             
      }
   }
   if (found)
          reallocate(frank,sizeof(int)*found);
   return;
}

1) Do you mean realloc?

2) How does that work? I mean, if you use realloc to remove an element from an array, which one does it delete?

Matt

Yes I do mean realloc - we have our own fornt-ends for memory management - and reallocate is the wrapper for realloc()


My bad.

@ jim:
Your code will actually delete everything after "bob" in the array.

@ matt:
When your program reallocates "frank", the frank pointer in main is left pointing at the previous allocated memory. You'll need to pass a pointer to a pointer if you want to change the passed in value. Also, if "bob" is not found in your array, you just end up chopping off the last element.

As for elegance, you might be able to write a few less lines if you look into memmove(). With that and realloc(), you could probably cut that function in half, and it would be somewhat cleaner.

This is fairly elegant, in my opinion

Code:

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

void print_data(const int *data, size_t len)
{
    size_t n = 0;
    printf("len = %d, data = ", len);
    for (; n < len; n++)
        printf("%d,", data[n]);
    printf("\n");
}//print_data

void remove_data(int key, int *data, size_t *plen)
{
    int *data_end = data + *plen;

    while (data < data_end)
    {
        if (*data == key)
        {
            (*plen)--;
            data_end--;
            memmove(data, data + 1, (int)data_end - (int)data);
            continue;
        }//if

        data++;
    }//while
}//remove_data

int main()
{
    int data[] = {0,0,1,2,0,3,4,0,5,6,7,0,8,9,0,};
    size_t data_sz = sizeof(data)/sizeof(data[0]);

    print_data(data, data_sz);
    remove_data(0, data, &data_sz);
    print_data(data, data_sz);

    return 0;
}//main

gg

@Seb: This not chopping up memory outside of main is probably what has been giving the creeps - because it seems like bad practice intuitively... but I'm not entirely sure what your code is doing so I'll have to work it out...