Memory allocation at runtime?

I wonder if someoen can help me in the right direction with this one.

I have a memory area allocated with malloc. The memory area is used to hold pointers to other memory areas, ok. I am allocating the memory area for the pointers in the beginning of my app. But how do I allocate new memory blocks at runtime when I need it and store the pointers?

I really didn't get the question.

What do u mean by "How do i allocate new memory blocks at runtime"....malloc does memory allocation at runtime. ????

For what do u want to alloacte new memory blocks...for the pointers stored in the memory block u had allocated thru malloc at the. ???...

Quote:

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Originally posted by gotyatech
I really didn't get the question.

What do u mean by "How do i allocate new memory blocks at runtime"....malloc does memory allocation at runtime. ????

For what do u want to alloacte new memory blocks...for the pointers stored in the memory block u had allocated thru malloc at the. ???...

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Example: I want to allocate a memory area when I press a button. The memory area must be 100 bytes. After that I want to store the pointer to that memory area in the first position of the memory area I allocated at the beginning of my app. The next time I press the button I want to allocate a new memory area with 100 bytes, and store the pointer to that memory area at position 2 at the memory area I allocated at the beginning of my app and so on...

So the memory area I allocated at the beginning of my app is only used to store pointers to different 100 byte sized memory areas that is allocated when I press my button.

A small example:

Code:

---

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

int main(void)
{
  unsigned char **map = NULL;

  /* allocate space for 10 pointers */
  if((map = malloc(sizeof(*map) * 10)) == NULL)
  {
      printf("malloc map failed\n");
      return 1;
  }

  /* allocate 100 bytes */
  if((map[0] = malloc(sizeof(**map) * 100)) == NULL)
  {
      printf("malloc map[0] failed\n");
      free(map);
      return 2;
  }

  /* map[0] is now pointing to 100 bytes of allocated memory */

  free(map[0]);
  free(map);
  return 0;
}

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Quote:

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Originally posted by Monster
A small example:

Code:

---

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

int main(void)
{
  unsigned char **map = NULL;

  /* allocate space for 10 pointers */
  if((map = malloc(sizeof(*map) * 10)) == NULL)
  {
      printf("malloc map failed\n");
      return 1;
  }

  /* allocate 100 bytes */
  if((map[0] = malloc(sizeof(**map) * 100)) == NULL)
  {
      printf("malloc map[0] failed\n");
      free(map);
      return 2;
  }

  /* map[0] is now pointing to 100 bytes of allocated memory */

  free(map[0]);
  free(map);
  return 0;
}

---

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Thanks, it seems that this was exactly what I needed :p

Quote:

---

Originally posted by Monster
A small example:

Code:

---

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

int main(void)
{
  unsigned char **map = NULL;

  /* allocate space for 10 pointers */
  if((map = malloc(sizeof(*map) * 10)) == NULL)
  {
      printf("malloc map failed\n");
      return 1;
  }

  /* allocate 100 bytes */
  if((map[0] = malloc(sizeof(**map) * 100)) == NULL)
  {
      printf("malloc map[0] failed\n");
      free(map);
      return 2;
  }

  /* map[0] is now pointing to 100 bytes of allocated memory */

  free(map[0]);
  free(map);
  return 0;
}

---

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Just one question:

This line > malloc(sizeof(*map) * 10)

This means that pointer size is 32 bits, right? So this memory area is in fact 40 bytes?

Yes, you're right:

malloc(sizeof(*map) * 10) = malloc(sizeof(char *) * 10) = malloc(4 * 10) = 40 bytes of memory