Thread: Where to put free in my program?

Code:

#include <stdio.h>
#include <stdlib.h>
//#include <crtdbg.h>  // do not remove

#define FLUSH while (getchar() != '\n')
#define MEM_ERROR printf("Not enough memory!\n")

// Prototype Declarations
double getNum(void);
double getNumbers(double **pptr);
double insertionSort(double **pptr, int counter);
double printTable(double *ptr, double **pptr, int counter);

int main (void)
{
       //Local Definitions
       double *ptr;
       double **pptr;
       int counter = 0;
       int i;

       //  Statements
       printf("\t\t Homework 3 - Pointer Applications:\n"
                  "\t\t    Insertion Sort and Pointers\n\n" );
       if(!(ptr = malloc(1000 * sizeof (double)))){
               printf("Not enough memory available.\n"); // no memory available
               exit(100);
       }
       counter = getNumbers(&ptr);// if input is too big

       ptr = realloc(ptr, counter * sizeof(double));
       if( pptr == NULL )
          MEM_ERROR;


       if(!(pptr = (double**) malloc(counter * sizeof ( double* )))){
               printf("Not enough memory available.\n"); // no memory available
               exit(100);
       }

       for(i = 0; i < counter; i++)
               pptr[i] = &(ptr[i]);

       insertionSort(pptr, counter);
       printTable(ptr, pptr, counter);
       //  printf( _CrtDumpMemoryLeaks() ? "Memory Leak\n" : "No Memory Leak\n");  // do not remove
       printf("\n\t\tEnd of Program\n"
                  "\n\t\tHave a great day!\n");

       return 0;

}

/************************************************
 Prompt the user to enter a valid integer number
 Pre: nothing
 Post: returns a valid integer
*/
double getNum(void)
{
       double num;
       while (scanf("%lg", &num) != 1)
       {
                     // scanf returns 1 if number read corrrectly
           FLUSH;    // to "consume" the invalid input
          printf("-*- Invalid number. Please re-enter: ");
       } // while


   return num;
}


double getNumbers(double **pptr)
{
int counter = 0;
double number;


       printf("\nPlease enter numbers and enter -1 when you are done: ");
       number = getNum();
       while(number!= -1){
               (*pptr)[counter] = number;
               number = getNum();
               counter++;

       }

       return counter;
}
//This function sorts the array of pointer into ascending order.
double insertionSort(double **pptr, int counter)
{
int i, j;
double *temp;

       for(i = 1; i < counter; i++)
       {
               temp = pptr[i];
               j = i - 1;
                       while(j >= 0 && *temp < *pptr[j])
                       {
                               pptr[j + 1] = pptr[j];
                               j = j - 1;
                       }
               pptr[j + 1] = temp;
       }//insertion sort
return;
}
/*This function prints the array in ascending and descending order
as well as the original order that the user put in*/
double printTable(double *ptr, double **pptr, int counter)
{
int i;
       printf("\nAscending\tOriginal\tDescending\n");
       for(i = 0; i < counter; i++)
       {
               printf("%lg\t\t%lg\t\t%lg\n", *(pptr[i]), ptr[i], *(pptr[counter - 1 - i]));
       }

}

-Okay, so I know that I need to use free twice in main(for ptr and pptr). But I am not sure where to put it. Is there a specific place? At the very end of main, or after allocating the memory?
Thank you for your time.

When you no longer need to use the memory pointed to by those pointers you want to free. Simple as that.

And please stop casting the return values of malloc. It's just not necessary.

Originally Posted by rags_to_riches

When you no longer need to use the memory pointed to by those pointers you want to free. Simple as that.

But, I'm not sure when that is. I don't want to crash the program. Intuitively, I want to put it at the very bottom on my program, but I know that I need to put it in main.

Hmm I put both of the frees in main after my printTable function call. Is that reasonable? The program worked fine when I ran it.

Originally Posted by iMalc

That's fine. However I suggest you turn your warnings on or up if necessary and pay attention to them, particularly the one about using an uninitialised varaible.

I'm running it in Unix and its not giving me any warnings... and seems to work fine.

I just get a bunch of "previously declared" statements that make no sense.