define max length for allocator

Hello everyone,


In MSDN length_error sample,

http://msdn2.microsoft.com/en-us/library/2af6btx2.aspx

it uses internal macro _SIZT, other than size_t. I have found in file xmemory, _SIZT is defined to size_t.

So, my questions are

1. why not use size_t directly, why use an internal name (begins with _)?

2. Do we have to use _SIZT when we define a customized allocator?


thanks in advance,
George

I'd put it down to lack of concentration on the part of the programmer who wrote the example.

Thanks CornedBee,


Sorry English is not my native language. I do not quite understand your points. Could you coment on my original 2 questions please? :-)

Quote:

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Originally Posted by CornedBee

I'd put it down to lack of concentration on the part of the programmer who wrote the example.

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regards,
George

_SIZT is a vendor/implementation specific macro. To answer your points;

1) Microsoft engineers would have used it just in case implementation details of their compiler/library change so an allocator no longer works with size_t. IMHO, this is just unnecessary future-proofing: size_t is unlikely to disappear from standards in the foreseeable future.

2) No. For custom allocators, use whatever data types or structures are required so your allocator can manage memory as required. There is no obligation to use _SIZT, just as there is no obligation to use size_t. As a rule of thumb, however, it is better to code something portably unless you have a specific reason not to. So it's better to use standardised language features (eg size_t) rather than vendor-specific ones (_SIZT).

Thanks grumpy,


Question answered.

Quote:

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Originally Posted by grumpy

_SIZT is a vendor/implementation specific macro. To answer your points;

1) Microsoft engineers would have used it just in case implementation details of their compiler/library change so an allocator no longer works with size_t. IMHO, this is just unnecessary future-proofing: size_t is unlikely to disappear from standards in the foreseeable future.

2) No. For custom allocators, use whatever data types or structures are required so your allocator can manage memory as required. There is no obligation to use _SIZT, just as there is no obligation to use size_t. As a rule of thumb, however, it is better to code something portably unless you have a specific reason not to. So it's better to use standardised language features (eg size_t) rather than vendor-specific ones (_SIZT).

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regards,
George