std::codecvt<InternT,ExternT,StateT>::max_length, do_max_length - cppreference.com (original) (raw)

| Defined in header | | | | -------------------------------------------------------------------------- | | ------------- | | (1) | | | | public: int max_length() const throw(); | | (until C++11) | | public: int max_length() const noexcept; | | (since C++11) | | (2) | | | | protected: virtual int do_max_length() const throw(); | | (until C++11) | | protected: virtual int do_max_length() const noexcept; | | (since C++11) |

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.

[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] Example

#include #include #include   int main() { std::cout << "In codecvt_utf8, the longest multibyte character is " << std::codecvt_utf8().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

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