30 Localization library [localization]

30.4 Standard locale categories [locale.categories]

30.4.3 The numeric category [category.numeric]

30.4.3.1 General [category.numeric.general]

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The classes num_get<> and num_put<> handle numeric formatting and parsing.
Virtual functions are provided for several numeric types.
Implementations may (but are not required to) delegate extraction of smaller types to extractors for larger types.250
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All specifications of member functions for num_put and num_get in the subclauses of [category.numeric] only apply to the specializations required in Tables 104 and 105 ([locale.category]), namely num_get<char>, num_get<wchar_t>, num_get<C, InputIterator>, num_put<char>, num_put<wchar_t>, and num_put<C, OutputIterator>.
These specializations refer to the ios_base& argument for formatting specifications ([locale.categories]), and to its imbued locale for the numpunct<> facet to identify all numeric punctuation preferences, and also for the ctype<> facet to perform character classification.
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Extractor and inserter members of the standard iostreams use num_get<> and num_put<> member functions for formatting and parsing numeric values ([istream.formatted.reqmts], [ostream.formatted.reqmts]).
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Parsing "-1" correctly into, e.g., an unsigned short requires that the corresponding member get() at least extract the sign before delegating.