free.c

c21Examples.rar

/* Using free() to release allocated dynamic memory. */

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

#define BLOCKSIZE 3000000

int main( void )
{
    void *ptr1, *ptr2;

    /* Allocate one block. */

    ptr1 = malloc(BLOCKSIZE);

    if (ptr1 != NULL)
        printf("\nFirst allocation of %d bytes successful.",BLOCKSIZE);
    else
    {
        printf("\nAttempt to allocate %d bytes failed.\n",BLOCKSIZE);
        exit(1);
    }

    /* Try to allocate another block. */

    ptr2 = malloc(BLOCKSIZE);

    if (ptr2 != NULL)
    {
        /* If allocation successful, print message and exit. */

        printf("\nSecond allocation of %d bytes successful.\n",
               BLOCKSIZE);
        exit(0);
    }

    /* If not successful, free the first block and try again.*/

    printf("\nSecond attempt to allocate %d bytes failed.",BLOCKSIZE);
    free(ptr1);
    printf("\nFreeing first block.");

    ptr2 = malloc(BLOCKSIZE);

    if (ptr2 != NULL)
        printf("\nAfter free(), allocation of %d bytes successful.\n",
               BLOCKSIZE);
    return 0;
}