Re: std::map question

From:

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 24 Oct 2007 10:08:21 GMT

Message-ID:

<pQETi.12096$ZA.7829@newsb.telia.net>

On 2007-10-24 10:38, Matthias Pfeifer wrote:

Hi there,

I have two std::map<index_type, value_type> where index_type is a nenum,
that will possible extend in the development process of my application,
so i do not know now what possible values it will take and value_types
vary. In the value_type of the map i want to accumulate pointers or
integers - and i have two maps for that. One where value_type is a
std::vector<mypointer> and one where value_type is unsigned long long.
Question is if i have to initialize my map for all possible index_type
values. If i have e.g.

enum my_index {A,B};

do i have to do

my_map[A]=value_type();
my_map[B]=value_type();

or if i can just do

my_map[A]+=calculate_new_value(); /* hoping that my_map[A] calls
value_type() implicitly... */

or in the pointer-case

my_map[A].insert(new_value()); /* same hope... */

Yes, that willwork. If "A" is not found in the map then a new key-value
pair is created where the key is "A" and the value is "value_type()",
then a reference to the newly created value is returned.

--
Erik Wikstr??m