Releasing Dynamically Allocated Memory - C Memory

C examples for Memory:free

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Introduction

To release the memory for a block of dynamically allocated memory, use this statement: 

free(pNumber);
pNumber = NULL;

The following code shows how to use pointers and dynamic memory allocation:

Demo Code

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

int main(void){
  unsigned long long *pPrimes = NULL;  // Pointer to primes storage area
  unsigned long long trial = 0;        // Integer to be tested
  bool found = false;                  // Indicates when we find a prime
  int total = 0;                       // Number of primes required
  int count = 0;                       // Number of primes found

  total = 5;/*from w  ww.  j  a v  a  2  s  .c  o  m*/

  pPrimes = (unsigned long long*)malloc(total*sizeof(unsigned long long));
  if(!pPrimes){
     printf("Not enough memory. It's the end I'm afraid.\n");
     return 1;
  }

  *pPrimes = 2ULL;                     // First prime
  *(pPrimes + 1) = 3ULL;               // Second prime
  *(pPrimes + 2) = 5ULL;               // Third prime
  count = 3;                           // Number of primes stored
  trial = 5ULL;                        // Set to the last prime we have

  while(count < total){
    trial += 2ULL;                     // Next value for checking

    // Divide by the primes we have. If any divide exactly - it's not prime
    for(int i = 1 ; i < count ; ++i)
    {
      if(!(found = (trial % *(pPrimes + i))))
        break;                         // Exit if zero remainder
    }

    if(found)                          // We got one - if found is true
      *(pPrimes + count++) = trial;    // Store it and increment count
  }
  for(int i = 0 ; i < total ; ++i)  {
    printf ("%12llu", *(pPrimes + i));
    if(!((i+1) % 5))
      printf("\n");                   // Newline after every 5
  }
  printf("\n");                       // Newline for any stragglers

  free(pPrimes);
  pPrimes = NULL;
  return 0;
}

Result


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