std::codecvt<InternT,ExternT,StateT>::max_length, do_max_length
From cppreference.com
| Defined in header <locale>
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| (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.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.
Example
Run this code
#include <codecvt> #include <iostream> #include <locale> 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) |
| [virtual] |
returns the number of ExternT characters necessary to produce one InternT character, if constant (virtual protected member function) |