std::ctype::widen, do_widen

 

C++

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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

 

std::ctype

Member functions

ctype::ctype

ctype::~ctype

ctype::isctype::do_is

ctype::scan_isctype::do_scan_is

ctype::scan_notctype::do_scan_not

ctype::toupperctype::do_toupper

ctype::tolowerctype::do_tolower

ctype::widenctype::do_widen

ctype::narrowctype::do_narrow

Member functions of ctype<char>

ctype<char>::ctype

ctype<char>::~ctype

ctype<char>::table

ctype<char>::classic_table

ctype<char>::is

ctype<char>::scan_is

ctype<char>::scan_not

 

Defined in header <locale>
public: CharT widen( char c ) const;	(1)
public: const char* widen( const char* beg, const char* end, CharT* dst ) const;	(2)
protected: virtual CharT do_widen( char c ) const;	(3)
protected: virtual const char* do_widen( const char* beg, const char* end, CharT* dst ) const;	(4)

1,2) public member function, calls the protected virtual member function do_widen of the most derived class.

3) Converts the single-byte character c to the corresponding wide character representation using the simplest reasonable transformation. Typically, this applies only to the characters whose multibyte encoding is a single byte (e.g. U+0000-U+007F in UTF-8).

4) For every character in the character array [beg, end), writes the corresponding widened character to the successive locations in the character array pointed to by dst.

Widening always returns a wide character, but only the characters from the basic source character set (latin letters, digits, and punctuations required to write a C++ program) are guaranteed to have a unique, well-defined, widening transformation, which is also guaranteed to be reversible (by narrow()). In practice, all characters whose multibyte representation is a single byte are usually widened to their wide character counterparts, and the rest of the possible single-byte values are usually mapped into the same placeholder value, typically CharT(-1).

Widening, if successful, preserves all character classification categories known to is().

Parameters

c	-	character to convert
dflt	-	default value to produce if the conversion fails
beg	-	pointer to the first character in an array of characters to convert
end	-	one past the end pointer for the array of characters to convert
dst	-	pointer to the first element of the array of char to fill

Return value

1,3) widened character

2,4) end

Example

Run this code

#include <locale>
#include <iostream>
 
void try_widen(const std::ctype<wchar_t>& f, char c)
{
    wchar_t w = f.widen(c);
    std::cout << "The single-byte character " << +(unsigned char)c
              << " widens to " << +w << '\n';
}
 
int main()
{
    std::locale::global(std::locale("cs_CZ.iso88592"));
    auto& f = std::use_facet<std::ctype<wchar_t>>(std::locale());
    std::cout << std::hex << std::showbase << "In Czech ISO-8859-2 locale:\n";
    try_widen(f, 'a');
    try_widen(f, '\xdf'); // German letter ß (U+00df) in ISO-8859-2
    try_widen(f, '\xec'); // Czech letter ě (U+011b) in ISO-8859-2
 
    std::locale::global(std::locale("cs_CZ.utf8"));
    auto& f2 = std::use_facet<std::ctype<wchar_t>>(std::locale());
    std::cout << "In Czech UTF-8 locale:\n";
    try_widen(f2, 'a');
    try_widen(f2, '\xdf'); 
    try_widen(f2, '\xec'); 
}

Output:

In Czech ISO-8859-2 locale:
The single-byte character 0x61 widens to 0x61
The single-byte character 0xdf widens to 0xdf
The single-byte character 0xec widens to 0x11b
In Czech UTF-8 locale:
The single-byte character 0x61 widens to 0x61
The single-byte character 0xdf widens to 0xffffffff
The single-byte character 0xec widens to 0xffffffff

See also

narrow	invokes do_narrow (public member function)
widen	widens characters (public member function of std::basic_ios)
btowc	widens a single-byte narrow character to wide character, if possible (function)