Re: a few stl container questions: allocators and comparers.

[sheam]

sheam wrote:
Ok one last question on using my custom allocator with std::map:

should the allocator's value_type template argument be of type
pair<mykey,myvalor just myval type? Both seem to compile and run fine.

i.e.,

map< int,
Test,
less<const int>,
CustomAllocator<Test my_map;

or

map< int,
Test,
less<const int>,
CustomAllocator<pair<const int,Test my_map;
Is the 'rebind' struct making them functionally equivilant?

Thanks.

~S

[sheam]

sheam wrote:

sheam wrote:
Ok one last question on using my custom allocator with std::map:

should the allocator's value_type template argument be of type
pair<mykey,myvalor just myval type? Both seem to compile and run fine.

i.e.,

map< int,
Test,
less<const int>,
CustomAllocator<Test my_map;

or

map< int,
Test,
less<const int>,
CustomAllocator<pair<const int,Test my_map;
Is the 'rebind' struct making them functionally equivilant?

Thanks.

~S

In fact, I get same results if I do this:
map< int,
Test,
less<const int>,
CustomAllocator<float my_map;

????

~S

[Kai-Uwe Bux]

sheam wrote:

sheam wrote:

>sheam wrote:
Ok one last question on using my custom allocator with std::map:

should the allocator's value_type template argument be of type
pair<mykey,myvalor just myval type? Both seem to compile and run fine.

i.e.,

map< int,
Test,
less<const int>,
CustomAllocator<Test my_map;

or

map< int,
Test,
less<const int>,
CustomAllocator<pair<const int,Test my_map;

This would be the usual choice.

>Is the 'rebind' struct making them functionally equivilant?

Thanks.

~S

In fact, I get same results if I do this:
map< int,
Test,
less<const int>,
CustomAllocator<float my_map;

The default allocator type is std::alloctor< value_type >. Internally,
std::map has to use nodes that are not of type value_type. Therefore, it ha
to use a rebind trick to get the right allocator type. That is the reason
why it could compile with float.

However, the standard says that

std::map< Key, T, C, A >::reference

is a typedef for A::reference. The same goes for pointer, const_reference,
and const_pointer. As soon as you use these, the first and last version
should fail.
Best

Kai-Uwe Bux

[Shea Martin]

Kai-Uwe Bux wrote:

>
However, the standard says that

std::map< Key, T, C, A >::reference

is a typedef for A::reference. The same goes for pointer, const_reference,
and const_pointer. As soon as you use these, the first and last version
should fail.

Thanks. I noticed that it was essentially resulting an allocation of
std::pair, so that is what I was using.

~S