std::isdigit(std::locale)

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Localizations library

Locales and facets
locale
use_facet	has_facet
Character classification
isspace isblank (C++11) iscntrl isupper islower isalpha	isdigit ispunct isxdigit isalnum isprint isgraph
Conversions
toupper tolower	wstring_convert (C++11) wbuffer_convert (C++11)
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
Facet categories
ctype ctype<char> codecvt collate messages time_get time_put	num_get num_put numpunct money_get money_put moneypunct
Locale-specific facets
ctype_byname codecvt_byname messages_byname collate_byname	time_get_byname time_put_byname numpunct_byname moneypunct_byname
Code conversion facets
codecvt_utf8 (C++11) codecvt_utf16 (C++11)	codecvt_utf8_utf16 (C++11) codecvt_mode (C++11)
C locale
setlocale localeconv lconv	LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME

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'',L'',L'',L'',L'',L'',L'',L'',L'',L''};
    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";
    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
 is a digit
 is a digit
 is a digit
 is NOT a digit
 is NOT a digit
 is NOT a digit

See also

isdigit	checks if a character is a digit (function)
iswdigit	checks if a wide character is a digit (function)