C++ custom allocators and STL containers

Question

I've been attempting to use a custom SecureAllocator with basic_string and the STL containers but I'm having very little luck.

typedef std::basic_string< char, std::char_traits< char >, SecureAllocator< char > > SecureString;

SecureString value = "hello, world!";

vector< SecureString > collection;

collection.push_back( value );


In file included from /Users/bcrowhurst/source/utility/string_impl.cpp:31:
In file included from /Users/bcrowhurst/build/../source/utility/string_impl.h:31:
/usr/bin/../lib/c++/v1/string:2162:19: error: invalid operands to binary expression ('allocator_type' (aka 'SecureAllocator<char>') and 'allocator_type')
        if (__alloc() != __str.__alloc())
            ~~~~~~~~~ ^  ~~~~~~~~~~~~~~~

Envirnoment

Mac OSX Lion

Apple clang version 3.1 (tags/Apple/clang-318.0.61) (based on LLVM 3.1svn)

Target: x86_64-apple-darwin11.4.0

Thread model: posix

Answer 1

You have to implement comparison operators for your allocator type, telling if they are 'equivalent' so they can be used interchangably (or not).

The requirement for comparing two allocators a1 == a2 is

returns true only if storage allocated from each can be deallocated via the other. operator== shall be reflexive, symmetric, and transitive, and shall not exit via an exception.

and for a1 != a2

the same as !(a1 == a2)