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

| Defined in header | | | | --------------------------------------------------------------------------------------------------------------------------------------------------------- | --- | | | public: int length( StateT& state, const ExternT* from, const ExternT* from_end, std::size_t max ) const; | (1) | | | protected: virtual int do_length( StateT& state, const ExternT* from, const ExternT* from_end, std::size_t max ) const; | (2) | |

1. Public member function, calls the member function do_length of the most derived class.

2. Attempts to convert the ExternT characters from the character array defined by [from, from_end), given initial conversion state state, to at most max InternT characters, and returns the number of ExternT characters that such conversion would consume. Modifies state as if by executing do_in(state, from, from_end, from, to, to + max, to) for some imaginary [to, to + max) output buffer.

[edit] Return value

The number of ExternT characters that would be consumed if converted by do_in() until either all from_end - from characters were consumed or max InternT characters were produced, or a conversion error occurred.

The non-converting specialization std::codecvt<char, char, std::mbstate_t> returns std::min(max, from_end - from).

[edit] Example

#include #include #include   int main() { using facet_type = std::codecvt<wchar_t, char, std::mbstate_t>;   // narrow multibyte encoding std::string s = "z\u00df\u6c34\U0001d10b"; // or u8"zß水𝄋" // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b"   std::locale loc("en_US.UTF-8"); facet_type const& codecvt_facet = std::use_facet(loc); std::mbstate_t mb = std::mbstate_t(); std::cout << "Only the first " << codecvt_facet.length(mb, s.data(), s.data() + s.size(), 2) << " bytes out of " << s.size() << " would be consumed" " to produce the first 2 characters\n"; }

Output:

Only the first 3 bytes out of 10 would be consumed to produce the first 2 characters

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | converts a string from ExternT to InternT, such as when reading from file (virtual protected member function) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |