generic insertion sort

So I have an insertion sort here that is supposed to take in any type of input. I have the insertion algorithm correctly. The problem is with the swapping of the pointers. I don't really see what I'm doing wrong.

Code:

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

void inssort (void *base, size_t nelem, size_t size,
              int (*compar) (void *, void *))
{
  //int i, j;

 
  for ( size_t i = 1 ; i <= nelem; i++ )
  {
      //size_t offset = size * i;
      void *element = (char *) base + i * size;
      //void *element2 = (char *) base + (i-1) * size;
 
      //(void) printf("element: %c  element2: %c\n", *(char*)element, *(char*)element2);
     
      //double *value = (double *) element;
      //double *value2 = (double *) element2;
      //printf("e1: %s  e2: %s\n", element, element2);
     
      int slot = i;
      //void *key = malloc ( 200);
      //memcpy( key, element, ((i+1)*size) - (i*size) );
     
      void *key =  element;
     
      //Move all values smaller than key up one position
      for ( ; slot > 0; --slot )
      {
        void *ele1 = (char *) base + slot * size;
        void *ele2 = (char *) base + (slot-1) * size;
     
        int cmp = (*compar)(ele1, ele2);
       
        if ( cmp > 0)
            break;
           
        ele1 = ele2;

      }
     
      element = key;
  }
  //free ( key);
} 

int numcmp( void *s1, void *s2)
{
  double *no1 = (double *) s1;
  double *no2 = (double *) s2;
 
  //(void) printf("v1: %lg  v2: %lg
", *no1, *no2);
 
  if ( *no1 < *no2 )
      return -1;
  else if ( *no1 > *no2 )
      return 1;
  else
      return 0;
}

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Here is the code used to call the function from main:

Code:

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inssort( array, nelem, sizeof *array, numcmp);

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The parameters are correct I'm assuming.

Code:

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void *ele1 = (char *) base + slot * size;       
void *ele2 = (char *) base + (slot-1) * size;
     
        int cmp = (*compar)(ele1, ele2);
         
        if ( cmp > 0)
            break;
           
        ele1 = ele2;

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You're not changing the array at all. All you are doing is changing where ele1 and ele2 point towards. If ele1 and ele2 were part of an array of pointers to the elements, than that would make sense, but they're just arbitrary pointers that you've created.

Try adding these to your code:

Code:

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        /*ele1 = ele2; */ /* In other words, get rid of this line. */
        char *temp = malloc(size);
        memcpy(temp, ele1, size);
        memcpy(ele1, ele2, size);
        memcpy(ele2, temp, size);

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Consider strengthening you compiler warning checking flags. If you use something like -ansi -pedantic -Wall -Werror, then it'll help you see what's wrong with your program.