Defined in header <locale> | ||
---|---|---|
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.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
#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
[virtual] | converts a string from externT to internT, such as when reading from file (virtual protected member function) |
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