std::codecvt<InternT,ExternT,StateT>::length, do_length

Header: <locale>

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

# Declarations

public:
int length( StateT& state, const ExternT* from, const ExternT* from_end,
std::size_t max ) const;

protected:
virtual int do_length( StateT& state, const ExternT* from, const ExternT* from_end,
std::size_t max ) const;

# 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.

# Example

#include <iostream>
#include <locale>
#include <string>
 
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<facet_type>(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";
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 75	C++98	the effect on state was not specified	specified
LWG 305	C++98	std::codecvt<wchar_t, char, std::mbstate_t>::do_lengthwas required to return std::min(max, from_end - from)	not required

# See also

do_in