Re: Help with some logic, best way to update a container.

From:

"Simon" <spambucket@example.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Sun, 8 Feb 2009 06:56:09 +0200

Message-ID:

<6v771iFih7nkU1@mid.individual.net>

"Joseph M. Newcomer" <newcomer@flounder.com> wrote in message
news:k0lso4l6m65h28m9j200ld2vh1tv6ntvnk@4ax.com...

But you said explicitly, if a value is in the old container but not in the
new container,
you want to delete it from the old container. Suppose you had

old: {A=1 B=2 C=3}
new{A=4 B=5 C=6}
result: {A=4 B=5 C=6}

old {A=1 B=2 C=3}
new {C=7 D=8}
result: {C=7 D=8}

As I said, both containers are not similar, the 'new' container contians
some information, but not all.
This would be true if the map was that straight forward 1-1 mapping of
values, but assuming I have something like

struct _MYSTRUCT
{
int some_value;
int some_othervalue;
void* some_pointer;
};
std::map<int, _MYSTRUCT*> _data;

and the new data was something diferent

struct _MYSTRUCTB
{
int some_value;
int some_othervalue;
};

void Update( const std::map<int, _MYSTRUCTB>& newData )
{
...
}

In the example above
I would update 'some_value' and 'some_othervalue' where the ID is found in
_data (spec-1)
I would create/new _MYSTRUCT* using the values given by newData, and make
some_pointer NULL. (spec-2)
I would delete items id that are not present in newData (spec-3).

Simon