Re: the correct way to delete a map

From:

Nick Keighley <nick_keighley_nospam@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 08 Nov 2007 03:12:48 -0800

Message-ID:

<1194520368.052362.216050@s15g2000prm.googlegroups.com>

On 8 Nov, 10:55, Nick Keighley <nick_keighley_nos...@hotmail.com>
wrote:

Hi,

I have a map containing pointers. When I destroy the map I want to
delete
all the pointers.

typedef std::map<std::string, const T*> Table;

void destroy_map ()
{
    for (Table::iterator i = table_.begin(); i != table_.end(); ++i)
    {
         delete (*i).second;
         table_.erase (i);
    }

}

this crashes. Does the erase() invalidate the iterator?

This was the code I found on the net (latout fixed a bit)

for (map::iterator itr = myMap.begin(); itr != myMap.end())
{
     if(itr->value == something)
          myMap.erase(itr++);
     else
           itr++;

}

which it is claimed is from Josuttis. I suppose the fact that it
didn't compile should of made me doubt this...

ah! more poking around on the net. erase() does invalidate the
iterator. That's why the net code does a post increment in the erase
call.
So preumably I want:-

void destroy_map ()
{
    for (Table::iterator i = table_.begin(); i != table_.end();)
    {
         delete (*i).second;
         table_.erase (i++);
    }
}

since this code is actually in a DTOR and table_ is member variable
would I be better leaving the destruction of the map to the DTOR?

class Symbol_table
{
public:
   Table table_;
   ~Symbol_table();
};

Symbol_table::~Symbol_table()
{
    for (Table::iterator i = table_.begin(); i != table_.end(); ++i)
         delete (*i).second;
}

should the for-loop be changed into an algorithm? for_each()?

--
Nick Keighley