Another 'pointer to pointer' question

From:
Christopher <cpisz@austin.rr.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 28 Jan 2009 01:29:24 -0800 (PST)
Message-ID:
<6218e562-7a9a-47a7-9a0e-bcc3439ccd7c@z1g2000yqn.googlegroups.com>
I want to expand on another post I had asked earlier, but change
something and see if it is still OK.

Old post summary:

Q-
I need to have an array of pointers to something. I do not know how
many I will have until runtime. How do you allocate? It needs to be in
the form: type **, because the API I am using asks for it in that
way.

A-
Use std::vector

#include <vector>

void some_function(int**);

class A
{
   A()
   {
      // append with push_back
      for (int i = 1; i < 4; ++i) {
         m_integers.push_back( new int(i) );
      }

      // pass to C API
      int** pint = &m_integers[0];
      some_function(pint);
   }

   // add copy, assignment and destructor
   // remember to delete the ints

private:
   std::vector<int*> m_integers;
};

That worked great. Now I am going to end up having alot of these
buffers, but only need to pass a few to the API. Which ones will be
dynamic. I want to see if I involve a map of pointers, if the code is
still going to be OK. I know a map is not contiguous like a vector,
but I don't know if it matters when I just store pointers in the map?

Lemme see if I can code this example:

#include <vector>

// In thier C API, the buffer is some other thing they do not describe
// I just get a pointer to it. I just made this a vector for the
example
typedef std::vector<int> Buffer;
void some_function(Buffer **);

class A
{
   A()
   {
      // Create the master collection of buffers
      Buffer * buffer = new Buffer();
      for (int i = 0; i < 3; ++i)
      {
         buffer->push_back(i);
      }
      m_master.push_back("Numbers", buffer);

      buffer = new Buffer();
      for (int i = 0; i < 3; ++i)
      {
         buffer->push_back(i);
      }
      m_master.push_back("Indices", buffer);

      buffer = new Buffer();
      for (int i = 0; i < 3; ++i)
      {
         buffer->push_back(i);
      }
      m_master.push_back("Kilometers", buffer);

      // Pass only the needed buffers to the C API
      m_current.push_back( m_master["Numbers"] );
      m_current.push_back( m_master["Indices"] );

      Buffer ** pBuffers = &(m_current[0]);
      some_function(pBuffers);
   }

   // add copy, assignment and destructor
   // remember to delete allocated memory

private:

   typedef std::map<std::string, Buffer *> MasterBufferCollection;
   MasterBufferCollection m_master;

   typedef std::vector<Buffer *> CurrentBuffers;
   CurrentBuffers m_current;
};

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