[Boost-users] [hash][vc-7_1] warning on boost::hash<std::size_t> [was Re: [multi_index] function object as key extractor?]

Gottlob Frege ha escrito:

On 3/16/07, Joaquín Mª López Muñoz wrote:

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Hello Andrew,

Andrew Holden ha escrito:

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Joaquín Mª López Muñoz wrote:

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Filip Konvi?ka ha escrito:

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Aye, I got the following warning that I could not get rid of (VC 7.1)

C:\Boost\include\boost-1_33_1\boost\functional\hash\hash.hpp(132) : warning C4267: 'argument' : conversion from 'size_t' to 'unsigned int', possible loss of data

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Looks like an overzealous or simply misguided warning. Can you please try the following?

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Same warning? If so, you might ask for inclusion of a suitable #pragma warning(disable...) to the Boost.Hash author.

Depending on your concern for portability, you might not want to dismiss this warning. VC 7.1 and 8.0 provide it as part of their 64 bit portability warnings (size_t will be 64 bits wide on 64-bit Windows, while unsigned int will remain 32 bits). A better way to eliminate the warning might be to switch off the 64 bit portability warnings in your project options.

I'm not advocating that the warning be completely disabled, but only in a selective manner inside Boost.Hash code by using #pragma warning(push) and #pragma warning(pop):

// boost/hash/hash.hpp #pragma warning(push) #pragma warning(disable:4267) ... #pragma warning(pop)

Maybe it would be better if boost::hash included a size_t version:

inline std::size_t hash_value(std::size_t v) { return v; }

If necessary, in cases where std::size_t == unsigned int, it could probably use is_same to make sure both versions didn't exist and cause warnings/errors.

Hello Tony, this does not work, as VC 8.0 (and I guess VC 7.1 too) treats (in 32 bit) std::size_t and unsigned int as the very same type except for /Wp64 diagnosis purposes. AFAICS you cannot even distinguish std::size_t from unsigned int with any template machinery, however smart --which is fine after all, since the standard mandates that std::size_t be a typedef of one of the fundamental integer types, thus ruling out the posibility that std::size_t is its own separate type. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo