Std::isdigit(std::locale) (3) Linux Manual Page

std::isdigit(std::locale) – std::isdigit(std::locale)

Synopsis

Defined in header<locale>

    template <class charT>

    bool isdigit(charT ch, const locale &loc);

Checks if the given character is classified as a digit by the given locale’s std::ctype facet.

Parameters

ch – character
loc – locale

Return value

Returns true if the character is classified as a digit, false otherwise.

Possible implementation

  template< class charT >
  bool isdigit( charT ch, const std::locale& loc ) {
      return std::use_facet<std::ctype<charT>>(loc).is(std::ctype_base::digit, ch);
  }

Example

// Run this code

#include <iostream>

#include <locale>

#include <string>

#include <set>
struct jdigit_ctype : std::ctype<wchar_t>

{
    std::set<wchar_t> jdigits{L'一', L'二', L'三', L'四', L'五', L'六', L'七', L'八', L'九', L'十'};
    bool do_is(mask m, char_type c) const
    {
        if ((m & digit) && jdigits.count(c))
            return true;           // Japanese digits will be classified as digits
        return ctype::do_is(m, c); // leave the rest to the parent class
    }
};
int main()

{
    std::wstring text = L"123一二三１２３";
    std::locale loc(std::locale(""), new jdigit_ctype);
    std::locale::global(std::locale(""));
    std::wcout.imbue(std::locale());
    for (wchar_t c : text)
        if (std::isdigit(c, loc))
            std::wcout << c << " is a digit\n";
        else
            std::wcout << c << " is NOT a digit\n";
}

Output:

  1 is a digit
  2 is a digit
  3 is a digit
  一 is a digit
  二 is a digit
  三 is a digit
  １ is NOT a digit
  ２ is NOT a digit
  ３ is NOT a digit

std::isdigit(std::locale) (3) Linux Manual Page