std::codecvt::max_length, std::codecvt::do_max_length

 

C++

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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 ctype_byname<char> 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_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME

 

std::codecvt

Member functions

codecvt::codecvt

codecvt::~codecvt

codecvt::out codecvt::do_out

codecvt::in codecvt::do_in

codecvt::unshift codecvt::do_unshift

codecvt::encoding codecvt::do_encoding

codecvt::always_noconv codecvt::do_always_noconv

codecvt::length codecvt::do_length

codecvt::max_length codecvt::do_max_length

 

Defined in header <locale>
public: int max_length() const	(1)
protected: int do_max_length() const	(2)

1) public member function, calls the member function do_max_length of the most derived class.

2) returns the maximum value that do_length(state, from, from_end, 1) can return for any valid range [from, from_end) and any valid state.

Return value

The maximum number of externT characters that could be consumed if converted by do_in() to produce one internT character.

The non-converting specialization std::codecvt<char, char, std::mbstate_t> returns 1

Notes

If the encoding is state-dependent (encoding() == -1), then more than max_length() external characters may be consumed to produce one internal character

Exceptions

noexcept specification:  

noexcept

  (since C++11)

Example

run this code

#include <locale>
#include <iostream>
#include <codecvt>
int main()
{
    std::cout << "In codecvt_utf8, the longest multibyte character is "
              << std::codecvt_utf8<wchar_t>().max_length() << " bytes long\n";
 
    std::cout << "In header-consuming codecvt_utf8, the longest multibyte character is "
              << std::codecvt_utf8<wchar_t,
                                   0x10ffff,
                                   std::consume_header>().max_length() << " bytes long\n";
 
    std::cout << "In this system's en_US.utf8, the longest multibyte character is "
              << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
                    std::locale("en_US.utf8")
              ).max_length() << " bytes long\n";
 
    std::cout << "In this system's zh_CN.gb18030, the longest multibyte character is "
              << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
                    std::locale("zh_CN.gb18030")
              ).max_length() << " bytes long\n";
}

Output:

In codecvt_utf8, the longest multibyte character is 4 bytes long
In header-consuming codecvt_utf8, the longest multibyte character is 7 bytes long
In this system's en_US.utf8, the longest multibyte character is 6 bytes long
In this system's zh_CN.gb18030, the longest multibyte character is 4 bytes long

See also

MB_CUR_MAX	maximum number of bytes in a multibyte character in the current C locale (macro variable)
do_encoding [virtual]	returns the number of externT characters necessary to produce one internT character, if constant (virtual protected member function)