std::codecvt::length,do_length(3) | C++ Standard Libary | std::codecvt::length,do_length(3) |
NAME¶
std::codecvt::length,do_length - std::codecvt::length,do_length
Synopsis¶
Defined in header <locale>
public:
int length( StateT& state,
const ExternT* from, (1)
const ExternT* from_end,
std::size_t max ) const;
protected:
virtual int do_length( StateT& state,
const ExternT* from, (2)
const ExternT* from_end,
std::size_t max ) const;
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.
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)
Example¶
// Run this code
#include <locale>
#include <string>
#include <iostream>
int main()
{
// 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::mbstate_t mb = std::mbstate_t();
std::cout << "Only the first " <<
std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
std::locale("en_US.utf8")
).length(mb, &s[0], &s[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
See also¶
do_in converts a string from externT to internT, such as when
reading from file
[virtual] (virtual protected member function)
2022.07.31 | http://cppreference.com |