197. max_size() underspecified

Section: 20.5.3.5 [allocator.requirements], 26.2 [container.requirements] Status: NAD Submitter: Andy Sawyer Opened: 1999-10-21 Last modified: 2016-02-10

Priority: Not Prioritized

View other active issues in [allocator.requirements].

View all other issues in [allocator.requirements].

View all issues with NAD status.

Discussion:

Must the value returned by max_size() be unchanged from call to call?

Must the value returned from max_size() be meaningful?

Possible meanings identified in lib-6827:

1) The largest container the implementation can support given "best case" conditions - i.e. assume the run-time platform is "configured to the max", and no overhead from the program itself. This may possibly be determined at the point the library is written, but certainly no later than compile time.

2) The largest container the program could create, given "best case" conditions - i.e. same platform assumptions as (1), but take into account any overhead for executing the program itself. (or, roughly "storage=storage-sizeof(program)"). This does NOT include any resource allocated by the program. This may (or may not) be determinable at compile time.

3) The largest container the current execution of the program could create, given knowledge of the actual run-time platform, but again, not taking into account any currently allocated resource. This is probably best determined at program start-up.

4) The largest container the current execution program could create at the point max_size() is called (or more correctly at the point max_size() returns :-), given it's current environment (i.e. taking into account the actual currently available resources). This, obviously, has to be determined dynamically each time max_size() is called.

Proposed resolution:

Rationale:

max_size() isn't useful for very many things, and the existing wording is sufficiently clear for the few cases that max_size() can be used for. None of the attempts to change the existing wording were an improvement.

It is clear to the LWG that the value returned by max_size() can't change from call to call.