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std::codecvt::max_length, do_max_length

From cppreference.com
< cpp‎ | locale‎ | codecvt
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.

Contents

[edit] Return value

The maximum number of ExternT characters that could be consumed if converted by in() to produce one InternT character.

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

[edit] Notes

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

[edit] Exceptions

(none) (until C++11)
noexcept specification:  
noexcept
  
(since C++11)

[edit] Example

#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

[edit] See also

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