1) Destructors.
  The why and how to.

2) Identify the bad code :

typedef struct struct_bitsi_fileId_list
{   
  int numberOfFileIds;
  unsigned int* fileIdList;
} AppBitsiFileIdList;


int main()
{
	Node* node;
	...
	AppBitsiFileIdList* fList=AppBitsiPeerGetFileIds(node);
	...
	...      
	MEM_free(fList); 
}

AppBitsiFileIdList* AppBitsiPeerGetFileIds(Node* node)
{
	AppBitsiFileIdList* fList=(AppBitsiFileIdList*) MEM_malloc(sizeof(AppBitsiFileIdList));
	...
	...
	fList->numberOfFileIds=4;
	newFileIdList=(unsigned int*) MEM_malloc(4*(numberOfFileIds+1));
	fList->fileIdList=newFileIdList;	

	return fList;
}

3) A very brief comment on exceptions and handling. Try/throw/catch
http://cplus.about.com/od/exceptions/