std::codecvt<InternT,ExternT,State>::max_length,do_max_length (3) - Linux Manuals

std::codecvt<InternT,ExternT,State>::max_length,do_max_length: std::codecvt<InternT,ExternT,State>::max_length,do_max_length

NAME

std::codecvt<InternT,ExternT,State>::max_length,do_max_length - std::codecvt<InternT,ExternT,State>::max_length,do_max_length

Synopsis

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

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 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

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

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