selecting dynamically created memory pools in c

Question

I made a function by which I can create memory pools but how can I select them after creating them?

boolean create_memory_pool(char *name, int size)
{
  boolean result;
  result = false;
  name = malloc(size));
  if( name != NULL)
    result = true;

  return result;
}

In main function if I created more than one 1 memory pools for example

int main()
{
  boolean x;
  x = create_memory_pool( "pool1", 1024);

  x = create_memory_pool( "pool2", 2048);
  x = create_memory_pool( "pool3", 2048);

  // now how to select pool1 or pool2 or pool3
}

what I am trying to do is create a function called select by which I can pass the name of pool and it returns some reference to the pool called.

boolean select( char *name)
{
  //return true if pool of name "name" is selected. 
}

I think I need to declare a global variable X which acts as a reference to currently selected pool which is NULL in the beginning. And on creating each memory pool I can pass the function "select(name)" in the end of "create memory pool" function so on creation of new memory pool it will be automatically selected to the global X. or I can pass the name of any pool which I want to select. but I am stuck in thinking about its implementation.

When you say "memory pool", what do you mean? It sounds as if you just mean a dynamically allocated string? A "memory pool" is generally something used in memory allocation implementations, it's something that holds "a pool of" available memory from which you can allocate, for instance. Your question is very confusing. — unwind
– unwind, Commented Nov 22, 2013 at 10:36
There is no relationship between the created pools and the name in the char * variable. In fact that value just gets ignored. If you want to store the pointers linked to a name, you will have to work the data structure yourself. Why do you think that such thing is possible directly as part of the C language is beyond me. — SJuan76
– SJuan76, Commented Nov 22, 2013 at 10:40
@SJuan76 sorry I am new to c. I was also thinking about list. — Deepak
– Deepak, Commented Nov 22, 2013 at 10:41

unwind · Accepted Answer · 2013-11-22 10:52:27Z

I have no idea what you're after. I first thought you just wanted strdup(), but I guess not.

If you want to access the allocated memory by name, then you need to store both the name and the allocated pointer.

Perhaps something like:

typedef struct {
  const char *name;
  void *base;
  size_t size;
} memory_pool;

Then you can implement:

memory_pool * memory_pool_new(const char *name, size_t size)
{
  memory_pool *p = malloc(sizeof *p + size);
  if(p != NULL)
  {
    p->name = name; /* Assumes name is string literal. */
    p->base = p + 1;
    p->size = size;
  }
  return p;
}

Then you can have an array of pools in your main program:

memory_pool *pools[3];
pools[0] = memory_pool_new("foo", 17);
pools[1] = memory_pool_new("bar", 42);
pools[2] = memory_pool_new("baz", 4711);

Now it's natural to write a function that can find a memory pool by name, in an arary:

memory_pool memory_pool_array_find(memory_pool **pools, size_t num,
                                   const char *name)
{
  for(size_t i = 0; i < num; ++i)
  {
    if(strmcp(pools[i]->name, name) == 0)
      return pools[i];
  }
  return NULL;
}

You can then use the above to find one of the pools you created:

memory_pool *foo = memory_pool_array_find(pools, 3, "foo");
if(foo != NULL)
  printf("found the memory pool %s, size %zu\n", foo->name, foo->size);

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